Introduction

Diodes are two-terminal electronic devices / components that functions as a one-way switch i.e., they allow current to flow only in one direction. These diodes are manufactured using semiconductor materials like Silicon, Germanium and Gallium Arsenide.

The two terminals of the diode are known as Anode and Cathode. Based on the potential difference between these two terminals, the operation of diode can be classified in two ways:

• If anode has higher potential than cathode, then the diode is said to be in Forward Bias and it allows current to flow.
• If cathode has higher potential than anode, then the diode is said to be in Reverse Bias and it doesn’t allow current to flow.

Different types of diodes have different voltage requirements. For Silicon Diodes, the forward voltage is 0.7V and for Germanium diodes, it is 0.3V. Usually, in Silicon Diodes, the dark band on one end of the diode indicates the Cathode terminal and the other terminal is anode.

One of the main application of Diodes is Rectification i.e., to convert AC to DC. Since diodes allow current to flow only in one direction and blocks current flow in the other direction, diodes are used in reverse polarity protector and transient protector applications.

There are many Different Types of diodes and some of them are listed below.

Different Types of Diodes

Let us now briefly see about few common types of diodes.

1. Small Signal Diode

It is a small device with disproportional characteristics whose applications are mainly involved at high frequency and very low current applications such as radios and televisions etc. To protect the diode from contamination it is enveloped with a glass so it is also named as Glass Passivated Diode. One of the popular diodes of this type is the 1N4148.

Appearance wise, signal diodes are very small when compared with power diodes. To indicate the cathode terminal, one edge is marked with black or red color. For applications at high frequencies, the performance of the small signal diode is very effective.

With respect to the other functionalities, the signal diodes usually have a small current carrying capability and power dissipation. Usually, these are in the range of 150mA and 500mW respectively.

The Small Signal Diode can be made of either Silicon or Germanium type semiconductor material, but the characteristics of the diode varies depending up on the doping material.

Small Signal Diodes are used in general purpose diode applications, high speed switching, parametric amplifiers and many other applications. Some important characteristics of Small Signal Diode are:

• Peak Reverse Voltage (V_PR) – It is the maximum reverse voltage that can be applied to the diode before it breaks down.
• Reverse Current (I_R) – The current (very small value) that flows when it is reverse biased.
• Maximum Forward Voltage at Peak Forward Current (V_F at I_F)
• Reverse Recovery Time – The time required for reverse current to fall down from forward current to I_R.

2. Large Signal Diode

These diodes have large PN junction layer. Thus, they are usually used in rectification i.e., converting AC to DC. The large PN Junction also increases the forward current carrying capacity and reverse blocking voltage of the diode. The large signal diodes are not suitable for high frequency applications.

The main applications of these diodes are in Power Supplies (rectifiers, converter, inverters, battery charging devices, etc.). In these diodes, the value of forward resistance is few Ohms and the value of reverse blocking resistance is in Mega Ohms.

Since it has high current and voltage performance, these can be used in electrical devices which are used to suppress high peak voltages.

3. Zener Diode

It is a passive element which works under the principle of ‘Zener Breakdown’. First produced by Clarence Zener in 1934, it is similar to normal diode in forward bias condition i.e., it allows current to flow.

But in reverse bias condition, the diode conducts only when the applied voltage reaches the breakdown voltage, known as Zener Breakdown. It is designed to prevent the other semiconductor devices from momentary voltage pulses. It acts as voltage regulator.

4. Light Emitting Diode (LED)

These diodes convert the electrical energy in to light energy. First production started in 1968. It undergoes electroluminescence process in which holes and electrons are recombined to produce energy in the form of light in forward bias condition.

In the early days, LEDs are very costly and used only in special application. But over the years, the cost of the LEDs has comedown significantly. This and the fact they are extremely power efficient, makes LEDs as the main source of lighting in homes, offices, streets (for street lighting as well as traffic lights), automobiles, mobile phones.

5. Constant Current Diodes

It is also known as Current-Regulating Diode or Current-Limiting Diode or Diode-Connected Transistor. The function of the diode is to regulate the voltage at a particular current.

It functions as a two terminal current limiter. In this, JFET acts as current limiter to achieve high output impedance. The constant current diode symbol is shown below.

6. Schottky Diode

In this type of diode, the junction is formed by contacting the semiconductor material with metal. Due to this, the forward voltage drop is decreased to a minimum. The semiconductor material is N-type silicon, which acts as an anode and metals such as Chromium, Platinum, Tungsten etc. acts as cathode.

Due to the metal junction, these diodes have high current conducting capability and hence the switching time is reduced. So, Schottky Diode has greater use in switching applications. Mainly because of the metal – semiconductor junction, the voltage drop is low, which in turn increases the diode performance and reduces power loss. So, these are used in high frequency rectifier applications. The symbol of Schottky diode is as shown below.

7. Shockley Diode

It was one of the first semiconductor devices to be invented. Shockley Diode has four layers. It is also called as PNPN diode. It is equal to a thyristor without a gate terminal, which means the gate terminal is disconnected. As there is no trigger input, the only way the diode can conduct is by providing forward voltage.

It stays ON once it turned “ON” and stays OFF once it turned “OFF”. The diode has two operating states conducting and non-conducting. In non-conducting state the diode conducts with less voltage.

The symbol of the Shockley diode is as follows:

Shockley Diode Applications

• Trigger switches for SCR.
• Acts as relaxation oscillator.

8. Step Recovery Diodes

It is also called as snap-off diode or charge-storage diode. These are the special type of diodes which stores the charge from positive pulse and uses in the negative pulse of the sinusoidal signals. The rise time of the current pulse is equal to the snap time. Due to this phenomenon, it has speed recovery pulses.

The applications of these diodes are in higher order multipliers and in pulse shaper circuits. The cut-off frequency of these diodes is very high which are nearly at Giga hertz order.

As multiplier, this diode has the cut-off frequency range of 200 to 300 GHz. In the operations which are performing at 10 GHz range, these diodes play a vital role. The efficiency is high for lower order multipliers. The symbol for this diode is as shown below.

9. Tunnel Diode

It is used as high-speed switch, with switching speed in the order of few nano-seconds. Due to tunneling effect it has very fast operation in microwave frequency region. It is a two-terminal device in which concentration of dopants is too high.

The transient response is being limited by junction capacitance plus stray wiring capacitance. Mostly used in microwave oscillators and amplifiers. It acts as most negative conductance device. Tunnel diodes can be tuned both mechanically and electrically. The symbol of tunnel diode is as shown below.

Tunnel Diode Applications

• Oscillatory circuits.
• Microwave circuits.
• Resistant to nuclear radiation.

10. Varactor Diode

These are also known as Varicap diodes. It acts like the variable capacitor. Operations are performed mainly at reverse bias state only. These diodes are very famous due to its capability of changing the capacitance ranges within the circuit in the presence of constant voltage flow.

They can be able to vary capacitance up to high values. In varactor diode, we can decrease or increase the depletion layer by changing the reverse bias voltage. These diodes have many applications as voltage-controlled oscillator for cell phones, satellite pre-filters etc. The symbol of varactor diode is given below.

Varactor Diode Applications

• Voltage-controlled capacitors
• Voltage-controlled oscillators
• Parametric amplifiers
• Frequency multipliers
• FM transmitters and Phase locked loops in radio, television sets and cellular phone

11. Laser Diode

Similar to LED in which active region is formed by p-n junction. Electrically laser diode is P-I-N diode in which the active region is in intrinsic region. Used in fiber optic communications, barcode readers, laser pointers, CD/DVD/Blu-ray reading and recording, Laser printing.

Laser Diode Types:

• Double Heterostructure Laser: Free electrons and holes available simultaneously in the region.
• Quantum Well Lasers: lasers having more than one quantum well are called multi quantum well lasers.
• Quantum Cascade Lasers: These are heterojunction lasers which enables laser action at relatively long wavelengths.
• Separate Confinement Heterostructure Lasers: To compensate the thin layer problem in quantum lasers we go for separate confinement heterostructure lasers.
• Distributed Bragg Reflector Lasers: It can be edge emitting lasers or VCSELS.

The symbol of the Laser Diode is as shown:

12. Transient Voltage Suppression Diode

In semiconductor devices, transients will occur due to the sudden change in the state voltage. They will damage the device’s output response. To overcome this problem, Voltage Suppression Diodes are used. The operation of voltage suppression diode is similar to Zener diode operation.

The operation of these diodes is normal as p-n junction diodes but at the time of transient voltage its operation changes. In normal condition, the impedance of the diode is high.  When any transient voltage occurs in the circuit, the diode enters in to the avalanche breakdown region in which a low impedance is provided.

It is very spontaneously because the avalanche breakdown duration ranges in Pico seconds. Transient voltage suppression diode will clamp the voltage to the fixed levels, mostly its clamping voltage is in minimum range.

These are having applications in the telecommunication fields, medical, microprocessors and signal processing. It responds to over voltages faster than Varistors or gas discharge tubes.

The symbol for Transient voltage suppression diode is as shown below.

The diode is characterized by:

• Leakage current
• Maximum reverse stand-off voltage
• Breakdown voltage
• Clamping voltage
• Parasitic capacitance
• Parasitic inductance
• Amount of energy it can absorb

13. Gold Doped Diodes

In these diodes, Gold is used as a dopant. These diodes are faster than other diodes. In these diodes, the leakage current in reverse bias condition is also less. Even at the higher voltage drop it allows the diode to operate in signal frequencies. In these diodes, Gold helps for the faster recombination of minority carriers.

14. Super Barrier Diodes

It is a rectifier diode having low forward voltage drop as Schottky diode with surge handling capability and low reverse leakage current as P – N junction diode. It was designed for high power, fast switching and low-loss applications. Super barrier rectifiers are the next generation rectifiers with low forward voltage than Schottky diode.

15. Peltier Diode

In this type of diode, it generates heat at the two-material junction of a semiconductor, which flows from one terminal to another terminal. This flow is done in only single direction which is same as the direction of current flow.

This heat is produced due to electric charge produced by the recombination of minority charge carriers. This is mainly used in cooling and heating applications. This type of diodes used as sensor and heat engine for thermo electric cooling.

16. Crystal Diode

This is also known as Cat’s whisker, which is a type of point contact diode. Its operation depends on the pressure of contact between semiconductor crystal and the point.

In this, a metal wire is present, which is pressed against the semiconductor crystal. In this, the semiconductor crystal acts as cathode and metal wire acts as anode. These diodes are obsolete in nature. Mainly used in microwave receivers and detectors.

Crystal Diode Applications

• Crystal diode rectifier
• Crystal diode detector
• Crystal radio receiver

17. Avalanche Diode

This is passive element works under principle of Avalanche Breakdown. It works in reverse bias condition. It results in a large current due to the ionization produced by P – N junction during reverse bias condition.

These diodes are specially designed to undergo breakdown at specific reverse voltage to prevent the damage. The symbol of the avalanche diode is as shown below:

Avalanche Diode Uses

• RF Noise Generation: It acts as source of RF for antenna analyzer bridges and also as white noise generators.
• Used in radio equipment and also in hardware random number generators.
• Microwave Frequency Generation: In this the diode acts as negative resistance device.
• Single Photon Avalanche Detector: These are high gain photon detectors used in light level applications.

18. Silicon Controlled Rectifier

It consists of three terminals they are anode, cathode and a gate. It is nearly equal to the Shockley diode. As its name indicates it is mainly used for the control purpose when small voltages are applied in the circuit. The symbol of the Silicon Controlled Rectifier is as shown below:

Modes of Operation:

1. Forward blocking mode (off state): In this J1 and J3 forward biased and J2 is reverse biased. It offers high resistance below breakover voltage and hence it is said to be off state.
2. Forward conduction mode (on state): By increasing the voltage at anode and cathode or by applying positive pulse at the gate we can turn ON. To turn off the only way is to decrease the current flowing through it.
3. Reverse blocking mode (off state): SCR blocking the reverse voltage is named as asymmetrical SCR. Mostly used in current source inverters.

19. Vacuum Diodes

Vacuum diodes consist of two electrodes which will acts as an anode and the cathode. Cathode is made up of Tungsten, which emits the electrons in the direction of anode. Always electron flow will be from cathode to anode only. So, it acts like a switch.

If the cathode is coated with oxide material, then the electrons emission capability is high. Anode is a bit long in size and in some cases their surface is rough to reduce the temperatures developing in the diode. The diode will conduct only in one case that is when the anode is positive with respect to cathode terminal. The symbol is as shown in figure:

20. PIN Diode

The improved version of the normal P-N junction diode gives the PIN diode. In PIN diode doping is not necessary. The intrinsic material i.e., the material which has no charge carriers, is inserted between the P and N regions, which increase the area of depletion layer.

When we apply forward bias voltage, the holes and electrons will be pushed into the intrinsic layer. At some point due to this high injection level, the electric field will conduct through the intrinsic material also. This field makes the carriers to flow from two regions. The symbol of PIN diode is as shown below:

PIN Diode Applications:

• RF Switches: PIN diode is used for both signal and component selection. For example, PIN diodes acts as range-switch inductors in low phase noise oscillators.
• Attenuators: it is used as bridge and shunt resistance in bridge-T attenuator.
• Photo Detectors: it detects x-ray and gamma ray photons.

21. Point Contact Devices

A gold or tungsten wire is used to act as the point contact to produce a PN junction region by passing a high electric current through it. A small region of PN junction is produced around the edge of the wire which is connected to the metal plate which is as shown in the figure.

In forward direction, its operation is quite similar but in reverse bias condition the wire acts like an insulator. Since this insulator is between the plates, the diode acts as a capacitor. In general, the capacitor blocks the DC currents but the AC currents can flow in the circuit at high frequencies. So, these are used to detect the high frequency signals.

22. Gunn Diode

Gunn diode is fabricated with n-type semiconductor material only. The depletion region of two N-type materials is very thin. When voltage increases in the circuit, the current also increases. After certain level of voltage, the current will exponentially decrease, thus this exhibits the negative differential resistance.

It has two electrodes with Gallium Arsenide and Indium Phosphide. Due to this, it has negative differential resistance. It is also termed as transferred electron device. It produces micro wave RF signals so it is mainly used in Microwave RF devices. It can also use as an amplifier. The symbol of Gunn diode is shown below:

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What is a Switch?

A Switch is a device which is designed to interrupt the current flow in a circuit. In simple words, a Switch can make or break an electrical circuit. Every electrical and electronics application uses at least one switch to perform ON and OFF operation of the device.

So, switches are a part of the control system and without it, control operation cannot be achieved. A switch can perform two functions, namely fully ON (by closing its contacts) or fully OFF (by opening its contacts).

When the contacts of a switch are closed, the switch creates a closed path for the current to flow and hence  load consumes the power from source. When the contacts of a switch are open, no power will be consumed by the load as shown in below figure.

Another important function of a Switch is to divert the flow of electric current in a circuit. Consider the following circuit. When the switch is in position A, the lamp 1 turns ON and while it is in position B, lamp 2 turns ON.

There are numerous applications of switch, found in wide variety of fields such as homes, automobiles, industrial, military, aerospace and so on. In home and office applications, we use simple rocker switches to turn ON and OFF appliances like lights, computers, fans etc. In some applications, multi way switching is employed (like building wiring), where two or more switches are connected to control an electrical load from more than one location, like a Two Way Switch, for example.

Characteristics of a Switch

Before proceeding further and looking at different types of switches, let us see some important points on the Characteristics of a Switch.

• The two important characteristics of a switch are its Poles and Throws. A pole represents a contact and a throw represents a contact-to-contact connection. Number of poles and throws are used to describe a switch.
• Some standard numbers of poles and throws are Single (1 pole or 1 throw) and Double (2 poles or 2 switches).
• If the number of poles or throws are greater than 2, then the number is often directly used. For example, a three pole six throw switch is often represented as 3P6T.
• Another important characteristic of a switch is its action i.e., whether it is a Momentary or Latched action. Momentary Switches (like push buttons, for example) are used to make momentary contact (for a brief time or as long the button is pressed).
• Latched Switches on the hand, maintain the contact until it is forced to the other position.

Types of Switches

Basically, Switches can be of two types. They are:

• Mechanical
• Electronic

Mechanical Switches are physical switches, which must be activated physically, by moving, pressing, releasing, or touching its contacts.

Electronic Switches, on the other hand, do not require any physical contact in order to control a circuit. These are activated by semiconductor action.

Mechanical Switches

Mechanical switches can be classified into different types based on several factors such as method of actuation (manual, limit and process switches), number of contacts (single contact and multi contact switches), number of poles and throws (SPST, DPDT, SPDT, etc.), operation and construction (push button, toggle, rotary, joystick, etc.), based on state (momentary and locked switches), etc.

Based on the number of poles and throws, switches are classified into following types. The pole represents the number of individual power circuits that can be switched. Most of the switches are designed have one, two or three poles and are designated as single pole, double pole and triple pole.

The number of throws represents the number of states to which current can pass through the switch. Most of the switches are designed to have either one or two throws, which are designated as single throw and double throw switches.

Single Pole Single Throw Switch (SPST)

• This is the basic ON and OFF switch consisting of one input contact and one output contact.
• It switches a single circuit and it can either make (ON) or break (OFF) the load.
• The contacts of SPST can be either normally open or normally closed configurations .

Single Pole Double Throw Switch (SPDT)

• This switch has three terminals: one is input contact and remaining two are output contacts.
• This means it consist two ON positions and one OFF position.
• In most of the circuits, these switches are used as changeover to connect the input between two choices of outputs.
• The contact which is connected to the input by default is referred as normally closed contact and contact which will be connected during ON operation is a normally open contact.

Double Pole Single Throw Switch (DPST)

• This switch consists of four terminals: two input contacts and two output contacts.
• It behaves like a two separate SPST configurations, operating at the same time.
• It has only one ON position, but it can actuate the two contacts simultaneously, such that each input contact will be connected to its corresponding output contact.
• In OFF position both switches are at open state.
• This type of switches is used for controlling two different circuits at a time.
• Also, the contacts of this switch may be either normally open or normally closed configurations.

Double Pole Double Throw Switch (DPDT)

• This is a dual ON/OFF switch consisting of two ON positions.
• It has six terminals, two are input contacts and remaining four are the output contacts.
• It behaves like a two separate SPDT configuration, operating at the same time.
• Two input contacts are connected to the one set of output contacts in one position and in another position, input contacts are connected to the other set of output contacts.

Push Button Switch

• It is a momentary contact switch that makes or breaks connection as long as pressure is applied (or when the button is pushed).
• Generally, this pressure is supplied by a button pressed by someone’s finger.
• This button returns its normal position, once the pressure is removed.
• The internal spring mechanism operates these two states (pressed and released) of a push button.
• It consists of stationary and movable contacts, of which stationary contacts are connected in series with the circuit to be switched while movable contacts are attached with a push button.
• Push buttons are majorly classified into normally open, normally closed and double acting push buttons as shown in the above figure.
• Double acting push buttons are generally used for controlling two electrical circuits.

Toggle Switch

• A toggle switch is manually actuated (or pushed up or down) by a mechanical handle, lever or rocking mechanism. These are commonly used as light control switches.
• Most of these switches come with two or more lever positions which are in the versions of SPDT, SPST, DPST and DPDT switch. These are used for switching high currents (as high as 10 A) and can also be used for switching small currents.
• These are available in different ratings, sizes and styles and are used for different type of applications. The ON condition can be any of their level positions, however, by convention the downward is the closed or ON position.

Limit Switch

• The control schemes of a limit switch are shown in above figure , in which four varieties of limit switches are presented.
• Some switches are operated by the presence of an object or by the absence of objects or by the motion of machine instead of human hand operation. These switches are called as limit switches.
• These switches consist of a bumper type of arm actuated by an object. When this bumper arm is actuated, it causes the switch contacts to change position.

Float Switches

• Float switches are mainly used for controlling DC and AC motor pumps according to the liquid or water in a tank or sump.
• This switch is operated when the float (or floating object) moves downward or upward based on water level in a tank.
• This float movement of rod or chain assembly and counterweight causes to open or close electrical contacts. Another form of float switch is the mercury bulb type switch that does not consist of any float rod or chain arrangement.
• This bulb consist of mercury contacts such that when the liquid level rises or falls, the state of contacts also changes.
• The ball float switch symbol is shown in the above figure. These float switches can be normally open or normally closed type.

Flow Switches

• These are mainly used to detect the movement of liquid or air flow through a pipe or duct. The air flow switch (or a micro switch) is constructed by a snap-action.
• This micro switch is attached to a metal arm .To this metal arm, a thin plastic or metal piece is connected.
• When a large amount of air passes through the metal or plastic piece, it causes the movement of metal arm and thus operates the contacts of the switch.
• Liquid flow switches are designed with a paddle that inserted across the flow of liquid in a pipe. When liquid flows through the pipe, force exerted against the paddle changes the position of the contacts.
• The above figure shows the switch symbol used for both air flow and liquid flow. The flag symbol on the switch indicates the paddle which senses the flow or movement of liquid.
• These switches again normally open or normally closed type configurations.

Pressure Switches

• These switches are commonly used in industrial applications in order to sense the pressure of hydraulic systems and pneumatic devices.
• Depends on the range of pressure to be measured, these pressure switches are classified into diaphragm operated pressure switch, metal bellow type pressure switch and piston type pressure switch.
• In all these types, pressure detection element operates a set of contacts (which can be either double pole or single pole contacts).
• This switch symbol consist a half-circle connected to a line in which flat part indicates a diaphragm. These switches may be either normally open or normally closed type configurations.

Temperature Switches

• The most common heat sensing element is the bimetallic strip that operates on the principle of thermal expansion.
• The bimetallic strips are made with two dissimilar metals (that are having different thermal expansion rates) and are bonded with each other.
• The switch contacts are operated when the temperature causes the strip to bend or wrap. Another method of operating the temperature switch is to use mercury glass tube.
• When the bulb is heated, mercury in the tube will expand and then generates pressure to operate the contacts.

Joystick Switch

• Joystick switches are manually actuated control devices used mainly in portable control equipment.
• It consists of a lever which moves freely in more than one axis of motion.
• Depending on the movement of the lever pushed, one or more switch contacts are actuated.
• These are ideally suited for lowering, raising and triggering movements to the left and right.
• These are used for building machinery, cable controls and cranes. The symbol for the joystick is shown below.

Rotary Switches

• These are used for connecting one line to one of many lines.
• Examples of these switches are range selectors in electrical metering equipment, channel selectors in communication devices and band selectors in multi-band radios.
• It consists of one or more moving contacts (knob) and more than one stationary contact.
• These switches are come with different arrangement of contacts such as single pole 12-way, 3-pole 4-way, 2-pole 6-way and 4-pole 3-way.

Electronic Switches

The electronic switches are generally called as Solid State switches because there are no physical moving parts and hence no physical contacts. Most of the appliances are controlled by semiconductor switches such as motor drives and HVAC equipment.

There are different types of solid state switches are available in todays consumer, industrial and automotive market with different sizes and ratings. Some of these solid state switches include transistors, SCRs, MOSFETs, TRIACs and IGBTs.

Bipolar Transistors

A transistor either allows the current to pass or it blocks the current as similar to working of normal switch.

In switching circuits, transistor operates in cut-off mode for OFF or current blocking condition and in saturation mode for ON condition. The active region of the transistor is not used for switching applications.

Both NPN and PNP transistors are operated or switched ON when a sufficient base current is supplied to it. When a small current flows though the base terminal supplied by a driving circuit (connected between the base and emitter), it causes the transistor to turn ON the collector-emitter path.

And it is turned OFF when the base current is removed and base voltage is reduced to a slight negative value. Even though it utilizes small base current, it is capable of carrying much higher currents through the collector- emitter path.

Power Diode

A diode can perform switching operations between its high and low state impedance states. Semiconductor materials like Silicon and Germanium are used for constructing the diodes.

Usually, Power Diodes are constructed using Silicon in order to operate the device at higher currents and higher junction temperatures. These are constructed by joining p and n type semiconductor materials together to form PN junction. It has two terminals namely anode and cathode.

When the anode is made positive with respect to cathode and by the application of voltage greater than the threshold level, PN junction is forward biased and starts conducting (like ON switch). When the cathode terminal is made positive with respect to anode, PN junction reverse biased and its blocks the current flow (like OFF switch).

MOSFET

Perhaps the most popular and most commonly used Semiconductor Switching Device is the MOSFET. Metal Oxide Semiconductor Field Effect Transistor (MOSFET) is a unipolar and high frequency switching device. It is most commonly used switching device is power electronic applications. It has three terminals namely drain (output), source (common) and gate (input).

It is a voltage controlled device i.e., by controlling the input (gate to source) voltage, resistance between the drain and source is controlled, which further determines the ON and OFF state of the device.

MOSFETs can be a P-Channel or N-Channel devices. The N-Channel MOSFET is tuned ON by applying a positive V_GS with respect to the source (provided that V_GS should be greater than threshold voltage).

P-channel MOSFET operates in a similar manner of N-channel MOSFET but it uses reverse polarity of voltages. Both V_GS and V_DD are negative with respect to the source to switch ON the P-channel MOSFET.

IGBT

IGBT (Insulated Gate Bipolar Transistor) combines the several advantages of bipolar junction power transistor and power MOSFET. Like a MOSFET, it is a voltage controlled device and has lower ON state voltage drop (less than that of MOSFET and closer to power transistor).

It is a three terminal semiconductor high speed switching device. These terminals are emitter, collector and gate.

Similar to the MOSFET, IGBT can be turned ON by applying a positive voltage (greater than the threshold voltage) between the gate and emitter. IGBT can be turned OFF by reducing the voltage across the gate-emitter to zero. In most of the cases, it needs a negative voltage to reduce the turn OFF losses and safely turn OFF the IGBT.

SCR

A Silicon Controlled Rectifier (SCR) is one of the most widely used high speed switching device for power control applications. It is a unidirectional device as a diode, consisting of three terminals, namely anode, cathode and gate.

An SCR is turned ON and OFF by controlling its gate input and biasing conditions of the anode and cathode terminals. SCR consists of four layers of alternate P and N layers such that boundaries of each layer forms junctions J1, J2 and J3.

TRIAC

Triac (or TRIode AC) switch is a bidirectional switching device, which is an equivalent circuit of two back to back SCRs connection with one gate terminal.

Its capability to control AC power in both positive and negative peaks of the voltage waveform often makes these devices to be used in motor speed controllers, light dimmers, pressure control systems, motor drives and other AC control equipment.

DIAC

A DIAC (or DIode AC Switch) is bidirectional switching device and it consists of two terminals, which are not named as anode and cathode as it is a bidirectional device i.e., a DIAC can be operated in either direction regardless of the terminal identification. This indicates that the DIAC can be used in either direction.

When a voltage is applied across a DIAC, it either operates in forward blocking or reverse blocking mode unless the applied voltage is less than the breakover voltage. Once the voltage is increased more than breakover voltage, avalanche breakover occurs and device starts conducting.

Gate Turn-Off Thyristor

A GTO (Gate Turn off Thyristor) is a bipolar semiconductor switching device. It has three terminals: an anode, a cathode and a gate. As the name implies, this switching device is capable to turn OFF through gate terminal.

A GTO is turned ON by applying a small positive gate current, which triggers the conduction mode. It can be turned OFF by a negative pulse to the gate. GTO symbol consists of double arrows on the gate terminal, which represents the bidirectional flow of current through gate terminal.

Conclusion

A simple tutorial on Switches, Different Types of Switches, Characteristics of a Switch, Mechanical Switches, Electronic Switches, circuit symbols of all the switches and also example circuits (or connections) for important switches.

The post What is a Switch? What are the Different Types of Switches? appeared first on ElectronicsHub.

Multiplexer

Multiplexer means many into one. A multiplexer is a circuit used to select and route any one of the several input signals to a single output. A simple example of an non-electronic circuit of a multiplexer is a single pole multi-position switch.

Multi-position switches are widely used in many electronics circuits. However, circuits that operate at high speed require the multiplexer to be automatically selected. A mechanical switch cannot perform this task efficiently. Therefore, multiplexer is used to perform high speed switching are constructed of electronic components.

Multiplexers can handle two type of data i.e., analog and digital. For analog application, multiplexer are built using relays and transistor switches. For digital application, they are built from standard logic gates.

The multiplexer used for digital applications, also called digital multiplexer, is a circuit with many input but only one output. By applying control signals (also known as Select Signals), we can steer any input to the output. Some of the common types of multiplexer are 2-to-1, 4-to-1, 8-to-1, 16-to-1 multiplexer.

Following figure shows the general idea of a multiplexer with n input signal, m control signals and one output signal.

Understanding 4-to-1 Multiplexer

The 4-to-1 multiplexer has 4 input bits, 2 control or select bits, and 1 output bit. The four input bits are D0,D1,D2 and D3. Only one of this is transmitted to the output Y. The output depends on the values of A and B, which are the control inputs. The control input determines which of the input data bit is transmitted to the output.

For instance, as shown in figure, when  A B = 0 0 , the upper AND gate is enabled, while all other AND gates are disabled. Therefore, data bit D0 is transmitted to the output, giving Y = Do.

If the control input is changed to  A B = 1 1 , all gates are disabled except the bottom AND gate. In this case, D3 is transmitted to the output and Y = D3.

• An example of 4-to-1 multiplexer is IC 74153 in which the output is same as the input.
• Another example of 4-to-1 multiplexer is 45352 in which the output is the compliment of the input.
• Example of 16-to-1 line multiplexer is IC 74150.

Applications of Multiplexer

Multiplexer are used in various fields where multiple data need to be transmitted using a single line. Following are some of the applications of multiplexers –

1. Communication System – Communication system is a set of system that enable communication like transmission system, relay and tributary station, and communication network. The efficiency of communication system can be increased considerably using multiplexer. Multiplexer allow the process of transmitting different type of data such as audio, video at the same time using a single transmission line.
2. Telephone Network – In telephone network, multiple audio signals are integrated on a single line for transmission with the help of multiplexers. In this way, multiple audio signals can be isolated and eventually, the desire audio signals reach the intended recipients.
3. Computer Memory – Multiplexers are used to implement huge amount of memory into the computer, at the same time reduces the number of copper lines required to connect the memory to other parts of the computer circuit.
4. Transmission from the Computer System of a Satellite – Multiplexer can be used for the transmission of data signals from the computer system of a satellite or spacecraft to the ground system using the GPS (Global Positioning System) satellites.

This is just an introduction to the concept of Multiplexer. To learn more about Multiplexers, read this Multiplexer (MUX) and Multiplexing tutorial.

Demultiplexer

Demultiplexer means one to many. A demultiplexer is a circuit with one input and many outputs. By applying control signal, we can steer any input to the output. Few types of demultiplexer are 1-to 2, 1-to-4, 1-to-8 and 1-to 16 demultiplexer.

Following figure illustrate the general idea of a demultiplexer with 1 input signal, m control signals, and n output signals.

Understanding 1-to-4  Demultiplexer

The 1-to-4 demultiplexer has 1 input bit, 2 control or select bits, and 4 output bits. An example of 1-to-4 demultiplexer is IC 74155. The 1-to-4 demultiplexer is shown in figure below-

The input bit is labelled as Data D. This data bit is transmitted to the selected output lines, which depends on the values of A and B, the control or Select Inputs.

When  A B = 0 1 , the second AND gate from the top is enabled while other AND gates are disabled. Therefore, data bit D is transmitted to the output Y1, giving Y1 = Data.

If D is LOW, Y1 is LOW. If D is HIGH, Y1 is HIGH. The value of Y1 depends upon the value of D. All other outputs are in low state.

If the control input is changed to  A B = 1 0 , all the gates are disabled except the third AND gate from the top. Then, D is transmitted only to the Y2 output, and Y2 = Data.

Example of 1-to-16 demultiplexer is IC 74154. It has 1 input bit, 4 control / select bits and 16 output bit.

Applications of Demultiplexer

1. Demultiplexer  is used to connect a single source to multiple destinations. The main application area of demultiplexer is communication system, where multiplexers are used. Most of the communication system are bidirectional i.e., they function in both ways (transmitting and receiving signals). Hence, for most of the applications, the multiplexer and demultiplexer work in sync. Demultiplexer are also used for reconstruction  of parallel data and ALU circuits.
2. Communication System – Communication system use multiplexer to carry multiple data like audio, video and other form of data using a single line for transmission. This process make the transmission easier.  The demultiplexer receive the output signals of the multiplexer and converts them back to the original form of the data at the receiving end. The multiplexer and demultiplexer work together to carry out the process of transmission and reception of data in communication system.
3. ALU (Arithmetic Logic Unit) – In an ALU circuit, the output of ALU can be stored in multiple registers or storage units with the help of demultiplexer. The output of ALU is fed as the data input to the demultiplexer. Each output of demultiplexer is connected to multiple register which can be stored in the registers.
4. Serial to Parallel Converter – A serial to parallel converter is used for reconstructing parallel data from incoming serial data stream.  In this technique, serial data from the incoming serial data stream is given as data input to the demultiplexer at the regular intervals. A counter is attach to the control input of the demultiplexer. This counter directs the data signal to the output of the demultiplexer where these data signals are stored. When all data signals have been stored, the output of the demultiplexer can be retrieved and read out in parallel.

This is just an introduction to the concept of Demultiplexer. To learn more about Demultiplexers, read this What is Demultiplexer (DEMUX) tutorial.

Conclusion

An introductory tutorial on Multiplexer and Demultiplexer. Learn the basics of Multiplexer, understand a basic 4-to-1 Multiplexer, applications of Multiplexer, Demultiplexer, a basic 1-to-4 Demultiplexer, applications of Demultiplexer.

The post Multiplexer and Demultiplexer appeared first on ElectronicsHub.

What is Multiplexing?

Multiplexing is the process of combining one or more signals and transmitting on a single channel. In analog communication systems, a communication channel is a scarce quantity, which must be properly used. For cost-effective and efficient use of a channel, the concept of Multiplexing is very useful as it allows multiple users to share a single channel in a logical way.

The three common types of Multiplexing approaches are:

• Time
• Frequency
• Space

Two of the best examples of Multiplexing Systems used in our day-to-day life are the landline telephone network and the Cable TV.

The device which is responsible for Multiplexing is known as Multiplexer. Multiplexers are used for both Analog and Digital signals. Let us focus on digital signals in this tutorial, to keep things simple. A multiplexer is the most frequently used combinational circuit and it is an important building block in many in digital systems.

These are mostly used to form a selected path between multiple sources and a single destination. A basic multiplexer has various data input lines and a single output line. These are found in many digital system applications such as data selection and data routing, logic function generators, digital counters with multiplexed displays, telephone network, communication systems, waveform generators, etc. In this article we are going to discuss about types of multiplexers and its design.

What is a Multiplexer?

The multiplexer or MUX is a digital switch, also called as data selector. It is a Combinational Logic Circuit with more than one input line, one output line and more than one select line. It accepts the binary information from several input lines or sources and depending on the set of select lines, a particular input line is routed onto a single output line.

The basic idea of multiplexing is shown in figure below in which data from several sources are routed to the single output line when the enable switch is ON. This is why, multiplexers are also called as ‘many to one’ combinational circuits.

The below figure shows the block diagram of a multiplexer consisting of n input lines, m selection lines and one output line. If there are m selection lines, then the number of possible input lines is 2^m. Alternatively, we can say that if the number of input lines is equal to 2^m, then m selection lines are required to select one of n (consider 2^m = n) input lines.

This type of multiplexer is referred to as 2ⁿ × 1 multiplexer or 2ⁿ-to-1 multiplexer. For example, if the number of input lines is 4, then two select lines are required. Similarly, to select one of 8 input lines, three select lines are required.

Generally, the number of data inputs to a multiplexer is a power of two such as 2, 4, 8, 16, etc. Some of the most frequently used multiplexers include 2-to-1, 4-to-1, 8-to-1 and 16-to-1 multiplexers.

These multiplexers are available in IC forms with different input and select line configurations. Some of the available multiplexer ICs include 74157 (Quad 2-to-1 MUX), 78158 (Quad 2-to-1 MUX with inverse output), 74153 (4-to-1 MUX), 74152 (8-to-1 MUX) and 74150 (16-to-1 MUX).

2-to-1 Multiplexer

A 2-to-1 multiplexer consists of two inputs D0 and D1, one select input S and one output Y. Depending on the select signal, the output is connected to either of the inputs. Since there are two input signals, only two ways are possible to connect the inputs to the outputs, so one select is needed to do these operations.

If the select line is low, then the output will be switched to D0 input, whereas if select line is high, then the output will be switched to D1 input. The figure below shows the block diagram of a 2-to-1 multiplexer which connects two 1-bit inputs to a common destination.

The truth table of the 2-to-1 multiplexer is shown below. Depending on the value of the select input, the inputs i.e., D0, D1 are produced at outputs. The output is D0 when Select value is S = 0 and the output is D1 when Select value is S = 1.

‘X’ in the above truth table denotes a don’t care condition. So, ignoring the don’t care conditions, we can derive the Boolean Expression of a typical 2 to 1 Multiplexer as follows:

 Y = SD0 + SD1 

From the above output expression, the logic circuit of 2-to-1 multiplexer can be implemented using logic gates as shown in figure. It consists of two AND gates, one NOT gate and one OR gate. When the select line, S=0, the output of the lower AND gate is zero, but the output of upper AND gate is D0. Thus, the output generated by the OR gate is equal to D0.

Similarly, when S=1, the output of the upper AND gate is zero, but the output of lower AND gate is D1. Therefore, the output of the OR gate is D1. Thus, the above given Boolean expression is satisfied by this circuit.

In order to efficiently use the Silicon, IC Manufacturers fabricate multiple Multiplexers in a single IC. Generally four 2 line to 1 line multiplexers are fabricated in a single IC. Some of the popular ICs of 2 to 1 multiplexers include IC 74157 and IC 74158.

Both these ICs are Quad 2-to-1 Multiplexers. While IC 74157 has a normal output, the IC74158 has an inverted output. There is only one selection line, which controls the input lines to the output in all four multiplexers.

The output Y0 can be either A0 or B0 depending on the status of the select line. Similarly, Y1 can be either A1 or B1, Y2 can be either A2 or B2 and so on. There is an additional Strobe or Enable control input E/Strobe, which enables and disables all the multiplexers, i.e., when E=1, outputs of all the multiplexer is zero irrespective of the value of S.

All the multiplexers are activated only when the E / Strobe input is LOW.

4-to-1 Multiplexer

A  4-to-1 multiplexer consists four data input lines as D0 to D3, two select lines as S0 and S1 and a single output line Y. The select lines S0 and S1 select one of the four input lines to connect the output line. The figure below shows the block diagram of a 4-to-1 multiplexer in which, the multiplexer decodes the input through select line.

The truth table of a 4-to-1 multiplexer is shown below in which four input combinations 00, 10, 01 and 11 on the select lines respectively switches the inputs D0, D2, D1 and D3 to the output. That means when S0=0 and S1 =0, the output at Y is D0, similarly Y is D1 if the select inputs S0=0 and S1= 1 and so on.

From the above truth table, we can write the output expressions as follows:

 Y = S0 S1 D0 + S0 S1 D1 + S0 S1 D2 + S0 S1 D3 

From the above expression of the output, a 4-to-1 multiplexer can be implemented by using basic logic gates. The below figure shows the logic circuit of 4:1 MUX which is implemented by four 3-inputs AND gates, two 1-input NOT gates, and one 4-inputs OR gate.

In this circuit, each data input line is connected as input to an AND gate and two select lines are connected as other two inputs to it. Additionally, there is also an Enable Signal. The output of all the AND gates are connected to inputs of OR gate in order to produce the output Y.

Generally, this type of multiplexers is available in IC with dual mode i.e., there will be two 4-to-1 Multiplexers in a single IC. The most common and popular 4-to-1 line multiplexer is IC 74153 which, is a dual 4-to-1 line multiplexer. It consists of two identical 4-to-1 multiplexers. It has two separate enable or strobe inputs to switch ON or OFF the individual multiplexers. But the Select lines are common to both the Multiplexers.

Usually, the enable input or strobe can be used to cascade two or more multiplexer ICs to construct a multiplexer with large number of inputs. Each multiplier is supplied with separate inputs. The figure below shows the pin diagram of IC74153.

8-to-1 Multiplexer

An 8-to-1 multiplexer consists of eight data inputs D0 through D7, three input select lines S0 through S2 and a single output line Y. Depending on the select lines combinations, multiplexer selects the inputs.

The below figure shows the block diagram of an 8-to-1 multiplexer with enable input that can enable or disable the multiplexer. Since the number data bits given to the MUX are eight, then 3 bits (2³ = 8) are needed to select one of the eight data bits.

The truth table for an 8-to1 multiplexer is given below with eight combinations of inputs so as to generate each output corresponds to input.

For example, if S2= 0, S1=1 and S0=0 then the data output Y is equal to D2. Similarly the data outputs D0 to D7 will be selected through the combinations of S2, S1 and S0 as shown in below figure.

From the above truth table, the Boolean equation for the output is given as:

 Y = S0 S1 S2 D0 + S0 S1 S2 D1 + S0 S1 S2 D2 + S0 S1 S2 D3 + S0 S1 S2 D4 + S0 S1 S2 D5 + S0 S1 S2 D6 + S0 S1 S2 D7 

From the above Boolean equation, the logic circuit diagram of an 8-to-1 multiplexer can be implemented by using 8 AND gates, 1 OR gate and 7 NOT gates as shown in below figure. In the circuit, when enable pin is set to one, the multiplexer will be disabled and if it is zero, then select lines will select the corresponding data input to pass through the output.

IC 74151 is a popular 8-to-1 multiplexer IC with eight inputs and two outputs. The two outputs are active low and active high outputs. It has three select lines A, B and C and one active low enable input. The pinout of this IC is given below.

8-to-1 Mux using 4-to-1 Mux and 2-to-1 Mux

If you observe the Boolean Expression of 8-to-1 Multiplexer shown above, we can re-write it as follows:

 Y = S0 S1 S2 D0 + S0 S1 S2 D1 + S0 S1 S2 D2 + S0 S1 S2 D3 + S0 S1 S2 D4 + S0 S1 S2 D5 + S0 S1 S2 D6 + S0 S1 S2 D7 

 Y = S0 (S1 S2 D0 + S1 S2 D1 + S1 S2 D2 + S1 S2 D3) + S0( S1 S2 D4 + S1 S2 D5 + S1 S2 D6 + S1 S2 D7) 

The expression in the first bracket i.e.,  S1 S2 D0 + S1 S2 D1 + S1 S2 D2 + S1 S2 D3  is similar to the Boolean Expression of a 4-to-1 Multiplexer with D0, D1, D2 and D3 as inputs and S1 and S2 as Select Lines. Let this expression be P1.

Similarly, the expression in the second bracket i.e.,  S1 S2 D4 + S1 S2 D5 + S1 S2 D6 + S1 S2 D7  is similar to the Boolean Expression of another 4-to-1 Multiplexer with D4, D5, D6 and D7 as inputs and S1 and S2 as Select Lines. Let this expression be P2.

Now, replacing the above expressions with P1 and P2, we get,

 S0 P1 + S0 P2 

This expression is similar to a 2-to-1 Multiplexer with P1 and P2 (where, P1 and P2 are outputs of respective 4-to-1 Multiplexers) as Inputs and S0 as Select Signal. So, finally, we can deduce that an 8-to-1 Multiplexer can be implemented using two 4-to-1 Multiplexers and one 2-to-1 Multiplexer. The block diagram of the same is shown below:

16-to-1 Multiplexer

All the higher order Multiplexers like 8-to-1, 16-to-1, etc. can be implemented using lower order multiplexers. But none-the-less, let us take a quick look at 16-to-1 Multiplexer. IC 74150 is a popular 16-to-1 Multiplexer IC. The inputs to a 16-to-1 MUX are D0, D1, D2 and so on up tp D15. Since it has 16 input lines, there will be 4 select lines namely S0, S1, S2 and S3.

The following image shows the block diagram of a typical 16-to-1 Multiplexer.

Simplified truth table for 16×1 Multiplexer is shown in the following table.

The Boolean Expression of a 16-to-1 Multiplexer is as follows:

 Y = S0 S1 S2 S3 D0 + S0 S1 S2 S3 D1 + S0 S1 S2 S3 D2 + S0 S1 S2 S3 D3 + S0 S1 S2 S3 D4 + S0 S1 S2 S3 D5 + S0 S1 S2 S3 D6 + S0 S1 S2 S3 D7 + S0 S1 S2 S3 D8 + S0 S1 S2 S3 D9 + S0 S1 S2 S3 D10 + S0 S1 S2 S3 D11 + S0 S1 S2 S3 D12 + S0 S1 S2 S3 D13 + S0 S1 S2 S3 D14 + S0 S1 S2 S3 D15 

The following image shows the logical circuit of a 16-to-1 Multiplexer.

Similar to an 8-to-1 Multiplexer, we can implement 16-to-1 Multiplexer using lower order multiplexers like 8-to-1, 4-to-1 and 2-to-1. The following image shows the block diagram of a 16-to-1 Multiplexer implemented using two 8-to-1 Multiplexers and one 2-to-1 Multiplexer.

Further, we can implement the individual 8-to-1 Multiplexers in the above image using two 4-to-1 Multiplexers and one 2-to-1 Multiplexer.

Application of Multiplexer

In all types of digital system applications, multiplexers find its immense usage. Since these allows multiple inputs to be connected independently to a single output, multiplexers are found in variety of applications including data routing, logic function generators, control sequencers, parallel-to-serial converters, etc.

Data Routing

Multiplexers are extensively used in data routing applications to route the data to a one particular destination from one of several sources. One of the applications includes the displaying of two multidigit BCD counters, one at a time. In such application, 74157 multiplexer ICs are used to select and display the content of either of two BCD counters using a set of decoder and LED displays.

Logic Function Generator

In place of logic gates, a logical expression can be generated by using a multiplexer. It is possible to connect the multiplexer such that it duplicates the logic of any truth table. In such cases it can generate the Boolean algebraic function of a set of input variables.

This abruptly reduces the number of logic gates or integrated circuits to perform the logic function since the multiplexer is a single integrated circuit. In this kind of applications, multiplexers are viewed as logic function generators.

For example consider the below logic diagram to implement the ex-OR function of three inputs. A 74151A 8-to-1 multiplexer is used in this logic generator. This multiplexer works exactly similar to the set of logic gates implementing the same function.

The output F is 1 for data inputs D1, D2, D5 and D6 which are selected by making selection lines to 001, 010, 100 and 111 respectively.

Parallel to Serial Conversion

A multiplexer circuit can be used to convert the parallel data to serial data in order to reduce the number of parallel buses by converting them to serial signals. This type of conversion is needed in telecommunication, test and measurement, military/aerospace, data communications applications.

Mostly in digital systems, data is processed in parallel for achieving higher speeds. But for transmission of the data signals over long distances, we need more number of lines. In such cases, parallel data is converted into serial form using multiplexers.

The figure below shows the parallel to serial data conversion using an 8 input multiplexer. Parallel data from the data in or some other register is applied to the 8 input lines of the multiplexer.

The selection codes for the multiplexer are generated by a 3-bit counter. With the application of each clock pulse to the counter the data is serially out from the multiplexer.

Other applications of multiplexers include control sequencers, pulse train generators, encoders, register to register data transfer, waveform generators, etc.

Conclusion

Complete tutorial on Multiplexer (MUX) and Multiplexing. You learned the basics of Multiplexing, multiplexer, different types of commonly used multiplexers like 2:1 MUX, 4:1 MUX, 8:1 MUX and 16:1 MUX, their Boolean Expressions, logic circuits and also couple of important applications of Multiplexers.

The post Multiplexer (MUX) and Multiplexing appeared first on ElectronicsHub.

The simplest of errors is corruption of a bit i.e., a 1 may be transmitted as a 0 or vice-versa. To confirm whether the received data is the intended data or not, we should be able to detect errors at the receiver.

In this tutorial, we will learn about Parity Bit, Even Parity, Odd Parity, Parity Generator and Parity Checker with a practical example and practical circuit.

What is Parity Bit?

The parity generating technique is one of the most widely used error detection techniques for the data transmission. In digital systems, when binary data is transmitted and processed, data may be subjected to noise so that such noise can alter 0s (of data bits) to 1s and 1s to 0s.

Hence, a Parity Bit is added to the word containing data in order to make number of 1s either even or odd. The message containing the data bits along with parity bit is transmitted from transmitter to the receiver.

At the receiving end, the number of 1s in the message is counted and if it doesn’t match with the transmitted one, it means there is an error in the data. Thus, the Parity Bit it is used to detect errors, during the transmission of binary data.

Parity Generator and Checker

A Parity Generator is a combinational logic circuit that generates the parity bit in the transmitter. On the other hand, a circuit that checks the parity in the receiver is called Parity Checker. A combined circuit or device of parity generators and parity checkers are commonly used in digital systems to detect the single bit errors in the transmitted data.

Even Parity and Odd Parity

The sum of the data bits and parity bits can be even or odd. In even parity, the added parity bit will make the total number of 1s an even number, whereas in odd parity, the added parity bit will make the total number of 1s an odd number.

The basic principle involved in the implementation of parity circuits is that sum of odd number of 1s is always 1 and sum of even number of 1s is always 0. Such error detecting and correction can be implemented by using Ex-OR gates (since Ex-OR gate produce zero output when there are even number of inputs).

To produce two bits sum, one Ex-OR gate is sufficient whereas for adding three bits, two Ex-OR gates are required as shown in below figure.

Parity Generator

It is combinational circuit that accepts an n-1 bit data and generates the additional bit that is to be transmitted with the bit stream. This additional or extra bit is called as a Parity Bit.

In even parity bit scheme, the parity bit is ‘0’ if there are even number of 1s in the data stream and the parity bit is ‘1’ if there are odd number of 1s in the data stream.

In odd parity bit scheme, the parity bit is ‘1’ if there are even number of 1s in the data stream and the parity bit is ‘0’ if there are odd number of 1s in the data stream. Let us discuss both even and odd parity generators.

Even Parity Generator

Let us assume that a 3-bit message is to be transmitted with an even parity bit. Let the three inputs A, B and C are applied to the circuit and output bit is the parity bit P. The total number of 1s must be even, to generate the even parity bit P.

The figure below shows the truth table of even parity generator in which 1 is placed as parity bit in order to make all 1s as even when the number of 1s in the truth table is odd.

The K-map simplification for 3-bit message even parity generator is

From the above truth table, the simplified expression of the parity bit can be written as

The above expression can be implemented by using two Ex-OR gates. The logic diagram of even parity generator with two Ex – OR gates is shown below. The three bit message along with the parity generated by this circuit which is transmitted to the receiving end where parity checker circuit checks whether any error is present or not.

To generate the even parity bit for a 4-bit data, three Ex-OR gates are required to add the 4-bits and their sum will be the parity bit.

Odd Parity Generator

Let us consider that the 3-bit data is to be transmitted with an odd parity bit. The three inputs are A, B and C and P is the output parity bit. The total number of bits must be odd in order to generate the odd parity bit.

In the given truth table below, 1 is placed in the parity bit in order to make the total number of bits odd when the total number of 1s in the truth table is even.

The truth table of the odd parity generator can be simplified by using K-map as

The output parity bit expression for this generator circuit is obtained as

P = A ⊕ (B ⊕ C)

The above Boolean expression can be implemented by using one Ex-OR gate and one Ex-NOR gate in order to design a 3-bit odd parity generator.

The logic circuit of this generator is shown in below figure, in which two inputs are applied at one Ex-OR gate, and this Ex-OR output and third input is applied to the Ex-NOR gate, to produce the odd parity bit. It is also possible to design this circuit by using two Ex-OR gates and one NOT gate.

Parity Check

It is a logic circuit that checks for possible errors in the transmission. This circuit can be an even parity checker or odd parity checker depending on the type of parity generated at the transmission end. When this circuit is used as even parity checker, the number of input bits must always be even.

Even Parity Checker

Consider that three input message along with even parity bit is generated at the transmitting end. These 4 bits are applied as input to the parity checker circuit, which checks the possibility of error on the data. Since the data is transmitted with even parity, four bits received at circuit must have an even number of 1s.

If any error occurs, the received message consists of odd number of 1s. The output of the parity checker is denoted by PEC (Parity Error Check).

The below table shows the truth table for the Even Parity Checker in which PEC = 1 if the error occurs, i.e., the four bits received have odd number of 1s and PEC = 0 if no error occurs, i.e., if the 4-bit message has even number of 1s.

The above truth table can be simplified using K-map as shown below.

The above logic expression for the even parity checker can be implemented by using three Ex-OR gates as shown in figure. If the received message consists of five bits, then one more Ex-OR gate is required for the even parity checking.

Odd Parity Checker

Consider that a three bit message along with odd parity bit is transmitted at the transmitting end. Odd parity checker circuit receives these 4 bits and checks whether any error are present in the data.

If the total number of 1s in the data is odd, then it indicates no error, whereas if the total number of 1s is even then it indicates the error since the data is transmitted with odd parity at transmitting end.

The below figure shows the truth table for odd parity generator where PEC =1 if the 4-bit message received consists of even number of 1s (hence the error occurred) and PEC= 0 if the message contains odd number of 1s (that means no error).

The expression for the PEC in the above truth table can be simplified by K-map as shown below.

After simplification, the final expression for the PEC is obtained as

PEC = (A Ex-NOR B) Ex-NOR (C Ex-NOR P)

The expression for the odd parity checker can be designed by using three Ex-NOR gates as shown below.

Parity Generator/Checker ICs

There are different types of parity generator /checker ICs are available with different input configurations such as 5-bit, 4-bit, 9-bit, 12-bit, etc. One of the most commonly used and standard type of parity generator/checker IC is 74180.

It is a 9-bit parity generator or checker used to detect errors in high speed data transmission or data retrieval systems. The figure below shows the pin diagram of 74180 IC.

This IC can be used to generate a 9-bit odd or even parity code or it can be used to check for odd or even parity in a 9-bit code (8 data bits and one parity bit).

This IC consists of eight parity inputs from A through H and two cascading inputs. There are two outputs even sum and odd sum. In implementing generator or checker circuits, unused parity bits must be tied to logic zero and the cascading inputs must not be equal.

If this IC is used as an Even Parity Checker and when a parity error occurs, the ‘sum even’ output goes low and ‘sum odd’ output goes high. If this IC is used as an Odd Parity Checker, the number of input bits should be odd, but if an error occurs the ‘sum odd’ output goes low and ‘sum even’ output goes high.

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Before going in to details of the Star Connection, Delta Connection and comparing those two, let us have a very brief note on three – phase electric power.

A single phase system consists of just two conductors (wires): one is called the phase (sometimes line, live or hot), through which the current flows and the other is called neutral, which acts as a return path to complete the circuit.

In a three – phase system, we have a minimum of three conductors or wires carrying AC voltages. It is more economical to transmit power using a 3 – phase power supply when compared to a single phase power supply as a three – phase supply can transmit three times the power with just three conductors when compared to a two – conductor single – phase power supply.

Hence, most of the power generated and distributed is actually a 3 – phase power (but majority of households will receive a single phase supply). To know more about single phase and three phase, read the Difference Between Single Phase and Three Phase Power Supplies tutorial.

Further, the three – phase electric power system can be arranged in two ways. They are: Star (also called Y or Wye) and Delta (Δ).

Star Connection

In a Star Connection, the 3 phase wires are connected to a common point or star point and Neutral is taken from this common point. Due to its shape, the star connection is sometimes also called as Y or Wye connection.

If only the three phase wires are used, then it is called 3 Phase 3 Wire system. If the Neutral point is also used (which often it is), the it is called 3 Phase 4 Wire system. The following image shows a typical Star Connection.

Delta Connection

In a Delta Connection, there are only 3 wires for distribution and all the 3 wires are phases (no neutral in a Delta connection). The following image shows a typical Delta Connection.

Comparison between Star and Delta Connections

Let us understand more about these connections by using the following Comparison between Star and Delta Connections.

The post Comparison between Star and Delta Connections appeared first on ElectronicsHub.

The main function of a computer port is to act as a point of attachment, where the cable from the peripheral can be plugged in and allows data to flow from and to the device.

A computer port is also called as a Communication Port as it is responsible for communication between the computer and its peripheral device. Generally, the female end of the connector is referred to as a port and it usually sits on the motherboard.

In Computers, communication ports can be divided into two types based on the type or protocol used for communication. They are Serial Ports and Parallel Ports.

A serial port is an interface through which peripherals can be connected using a serial protocol which involves the transmission of data one bit at a time over a single communication line. The most common type of serial port is a D-Subminiature or a D-sub connector that carry RS-232 signals.

A parallel port, on the other hand, is an interface through which the communication between a computer and its peripheral device is in a parallel manner i.e. data is transferred in or out in parallel using more than one communication line or wire. Printer port is an example of parallel port.

The article gives a brief introduction to different types of ports along with their applications.

PS/2

PS/2 connector is developed by IBM for connecting mouse and keyboard. It was introduced with IBM’s Personal Systems/2 series of computers and hence the name PS/2 connector. PS/2 connectors are color coded as purple for keyboard and green for mouse.

PS/2 is a 6-pin DIN connector. The pin out diagram of a PS/2 female connector is shown below.

Even though the pinout of both mouse and keyboard PS/2 ports are same, computers do not recognize the devise when connected to wrong port.

PS/2 port is now considered a legacy port as USB port has superseded it and very few of the modern motherboards include it as a legacy port.

Serial Port

Even though the communication in PS/2 and USB is serial, technically, the term Serial Port is used to refer the interface that is compliant to RS-232 standard. There are two types of serial ports that are commonly found on a computer: DB-25 and DE-9.

DB-25

DB-25 is a variant of D-sub connector and is the original port for RS-232 serial communication. They were developed as the main port for serial connections using RS-232 protocol but most of the applications did not require all the pins.

Hence, DE-9 was developed for RS-232 based serial communication while DB-25 was rarely used as a serial port and often used as a parallel printer port as a replacement of the Centronics Parallel 36 pin connector.

DE-9 or RS-232 or COM Port

DE-9 is the main port for RS-232 serial communication. It is a D-sub connector with E shell and is often miscalled as DB-9. A DE-9 port is also called as a COM port and allows full duplex serial communication between the computer and it’s peripheral.

Some of the applications of DE-9 port are serial interface with mouse, keyboard, modem, uninterruptible power supplies (UPS) and other external RS-232 compatible devices.

The pinout diagram of DE-9 port is shown below.

The use of DB-25 and DE-9 ports for communication is in decline and are replaced by USBs or other ports.

Parallel Port or Centronics 36 Pin Port

Parallel port is an interface between computer and peripheral devices like printers with parallel communication. The Centronics port is a 36 pin port that was developed as an interface for printers and scanners and hence a parallel port is also called as a Centronics port.

Before the wide use of USB ports, parallel ports are very common in printers. The Centronics port was later replaced by DB-25 port with parallel interface.

Audio Ports

Audio ports are used to connect speakers or other audio output devices with the computer. The audio signals can be either analogue or digital and depending on that the port and its corresponding connector differ.

Surround Sound Connectors or 3.5 mm TRS Connector

It is the most commonly found audio port that can be used to connect stereo headphones or surround sound channels. A 6 connector system is included on majority of computers for audio out as well as a microphone connection.

The 6 connectors are color coded as Blue, Lime, Pink, Orange, Black and Grey. These 6 connectors can be used for a surround sound configuration of up to 8 channels.

S/PDIF / TOSLINK

The Sony/Phillips Digital Interface Format (S/PDIF) is an audio interconnect used in home media. It supports digital audio and can be transmitted using a coaxial RCA Audio cable or an optical fiber TOSLINK connector.

Most computers home entertainment systems are equipped with S/PDIF over TOSLINK. TOSLINK (Toshiba Link) is most frequently used digital audio port that can support 7.1 channel surround sound with just one cable. In the following image, the port on the right is an S/PDIF port.

Video Ports

VGA Port

VGA port is found in many computers, projectors, video cards and High Definition TVs. It is a D-sub connector consisting of 15 pins in 3 rows. The connector is called as DE-15.

VGA port is the main interface between computers and older CRT monitors. Even the modern LCD and LED monitors support VGA ports but the picture quality is reduced. VGA carries analogue video signals up to a resolution of 648X480.

With the increase in use of digital video, VGA ports are gradually being replaced by HDMI and Display Ports. Some laptops are equipped with on-board VGA ports in order to connect to external monitors or projectors. The pinout of a VGA port is shown below.

Digital Video Interface (DVI)

DVI is a high speed digital interface between a display controller like a computer and a display device like a monitor. It was developed with an aim of transmitting lossless digital video signals and replace the analogue VGA technology.

There are three types of DVI connectors based on the signals it can carry: DVI-I, DVI-D and DVI-A. DVI-I is a DVI port with integrated analogue and digital signals. DVI-D supports only digital signals and DVI-A supports only analogue signals.

The digital signals can be either single link or dual link where a single link supports a digital signal up to 1920X1080 resolution and a dual link supports a digital signal up to 2560X1600 resolution. The following image compares the structures of DVI-I, DVI-D and DVI-A types along with the pinouts.

Mini-DVI

Mini-DVI port is developed by Apple as an alternative to Mini-VGA port and is physically similar to one. It is smaller than a regular DVI port.

It is a 32 pin port and is capable of transmitting DVI, composite, S-Video and VGA signals with respective adapters. The following image shows a Mini-DVI port and its compatible cable.

Micro-DVI

Micro-DVI port, as the name suggests is physically smaller than Mini-DVI and is capable of transmitting only digital signals.

This port can be connected to external devices with DVI and VGA interfaces and respective adapters are required. In the following image, a Micro-DVI port can be seen adjacent to headphone and USB ports.

Display Port

Display Port is a digital display interface with optional multiple channel audio and other forms of data. Display Port is developed with an aim of replacing VGA and DVI ports as the main interface between a computer and monitor.

The latest version DisplayPort 1.3 can handle a resolution up to 7680 X 4320.

The Display Port has a 20 pin connector, which is a very less number when compared to DVI port and offers better resolution. The pin out diagram of a Display Port is shown below.

Update: DisplayPort 1.4a is the latest (in production) version of DisplayPort Specification with support for 4K (3840 x 2160) at 120 Hz or 8K (7680 x 4320) at 60 Hz. An improved DisplayPort version 2.0 specification is released in June of 2019 with an increased bandwidth of 77.37 Gbps (approximately).

Mini DisplayPort

Apple introduced a miniature version of DisplayPort and called it Mini DisplayPort (mDP or Mini DP). Even though Mini DisplayPort has 20 pins, the physical size of the connector is smaller than a regular DisplayPort and the pin out is also different.

Most laptops provide Mini DisplayPort as an additional video out option in addition to HDMI.

RCA Connector

RCA Connector can carry composite video and stereo audio signals over three cables. Composite video transmits analogue video signals and the connector is as yellow colored RCA connector.

The video signals are transmitted over a single channel along with the line and frame synchronization pulses at a maximum resolution of 576i (standard resolution).

The red and white connectors are used for stereo audio signals (red for right channel and white for left channel).

Component Video

Component Video is an interface where the video signals are split into more than two channels and the quality of the video signal is better that Composite video.

Like composite video, component video transmits only video signals and two separate connectors must be used for stereo audio. Component video port can transmit both analogue and digital video signals.

The ports of the commonly found Component video uses 3 connectors and are color coded as Green, Blue and Red.

S-Video

S-Video or Separate Video connector is used for transmitting only video signals. The picture quality is better than that of Composite video but has a lesser resolution than Component video.

The S-Video port is generally black in color and is present on all TVs and most computers. S-Video port looks like a PS/2 port but consists of only 4 pins.

Out of the 4 pins, one pin is used to carry the intensity signals (black and white) and other pin is used to carry color signals. Both these pins have their respective ground pins. The pinout diagram of an S-Video port is shown below.

HDMI

HDMI is an abbreviation of High Definition Media Interface. HDMI is a digital interface to connect High Definition and Ultra High Definition devices like Computer monitors, HDTVs, Blu-Ray players, gaming consoles, High Definition Cameras etc.

HDMI can be used to carry uncompressed video and compressed or uncompressed audio signals. The HDMI port of type A is shown below.

The HDMI connector consists of 19 pins and the latest version of HDMI i.e. HDMI 2.0 can carry digital video signal up to a resolution of 4096×2160 and 32 audio channels. The pinout diagram of an HDMI port is as follows.

Update: The latest version of HDMI is 2.1 with much improved bandwidth, resolution and support from video card manufacturers. While HDMI 2.0 has a data bandwidth of 18 Gbps, the HDMI 2.1 has a staggering 48 Gbps of bandwidth. Coming to the display resolution, HDMI 2.1 supports 4K and 8K at 120 Hz refresh rate. Most modern (at least high end) graphics cards like Nvidia RTX 3090 provide at least a couple of HDMI 2.1 Ports to connect with monitors and TVs.

Mini HDMI

With HDMI 1.3 Version, a new HDMI Port and Connector combination is released called the Mini HDMI. Physically, it is smaller than a regular HDMI Port but has same 19 Pin. Intended for portable devices like laptops, cameras, camcorders, the Mini HDMI Port isn’t that popular.

Micro HDMI

HDMI developers introduced a new HDMI Connector and Port called Micro HDMI with HDMI Version 1.4. Micro HDMI also has 19 pins (just like regular HDMI and Mini HDMI) but the pinout is different.

Micro HDMI is often used in cameras, single board computers (like Raspberry Pi 4), etc. where physically it is difficult to include a regular HDMI port.

The size of Micro HDMI is significantly smaller than regular HDMI and has some resemblance to a micro–USB Port (sometimes people confuse among the two). The port on the left is a micro USB port and the one on the right is a micro HDMI Port.

USB

Universal Serial Bus (USB) replaced serial ports, parallel ports, PS/2 connectors, game ports and power chargers for portable devices.

USB port can be used to transfer data, act as an interface for peripherals and even act as power supply for devices connected to it. There are three kinds of USB ports: Type A, Type B or mini USB and Micro USB.

USB Type A

USB Type-A port is a 4 pin connector. There are different versions of Type – A USB ports: USB 1.1, USB 2.0 and USB 3.0. USB 3.0 is the common standard and supports a data rate of 400MBps.

USB 3.1 is also released and supports a data rate up to 10Gbps. Usually, but not all the times, the USB 2.0 is Black color coded and USB 3.0 is Blue. The following image shows USB 2.0 and USB 3.0 ports.

The pinout diagram of USB Type – A port is shown below. The pinout is common to all standards of Type – A.

USB Type C

USB Type – C is the latest specification of the USB and is a reversible connector. USB Type – C is supposed to replace Types A and B and is considered future proof.

The port of USB Type – C consists of 24 pins. The pinout diagram of USB Type – C is shown below. The latest USB Specifications (USB4) is an USB-C only specification i.e., only USB type C devices can be used with USB4 specifications.

In the latest USB4 specification, USB Type C Devices can support speeds up to 40 Gbps.

USB Power Delivery specifications allow USB devices to supply power to devices connected to the USB Port. USB Type – C can handle a current of 5A at 20V (only Power Delivery certified USB Type-C Ports).

This feature of handling high current is used in the latest Fast Charging Technology where a Smart Phone’s battery will reach its full charge is very less time. So, USB Type C Ports can provide up to 100W of power (which can be used for charging mobile phones and laptops).

In fact, the latest Apple M1 Mac Books use 61W USB C Power Adapter.

RJ-45

Ethernet is a networking technology that is used to connect your computer to Internet and communicate with other computers or networking devices.

The interface that is used for computer networking and telecommunications is known as Registered Jack (RJ) and RJ – 45 port in particular is used for Ethernet over cable. RJ-45 connector is an 8 pin – 8 contact (8P – 8C) type modular connector.

The latest Ethernet technology is called Gigabit Ethernet and supports a data transfer rate of over 10Gigabits per second. The Ethernet or a LAN port with 8P – 8C type connector along with the male RJ-45 cable is shown below.

The un-keyed 8P – 8C modular connector is generally referred to the Ethernet RJ-45. Often, RJ-45 ports are equipped with two LEDs for indicating transmission and packet detection.

As mentioned earlier, an Ethernet RJ-45 port has 8 pins and the following picture depicts the pinout of one.

RJ-11

RJ-11 is another type of Registered Jack that is used as an interface for telephone, modem or ADSL connections. Even though computers are almost never equipped with an RJ-11 port, they are the main interface in all telecommunication networks.

RJ-45 and RJ11 ports look alike but RJ-11 is a smaller port and uses a 6 point – 4 contact (6P – 4C) connector even though a 6 point – 2 contact (6P – 2C) is sufficient. The following is a picture of an RJ-11 port and its compatible connector.

The following image can be used to compare RJ-45 and RJ-11 ports.

e-SATA

e-SATA is an external Serial AT Attachment connector that is used as an interface for connecting external mass storage devices. Modern e-SATA connector are called e-SATAp and stands for Power e-SATA ports.

They are hybrid ports capable of supporting both e-SATA and USB. Neither the SATA organization nor the USB organization has officially approved the e-SATAp port and must be used at user’s risk.

The above image is of an e-SATAp port. It shows that both e-SATA and USB devices can be connected.

The post 16 Types of Computer Ports and Their Functions appeared first on ElectronicsHub.

All these and many other automation tasks are possible because of Sensors. Before going in to the details of What is a Sensor, What are the Different Types of Sensors and Applications of these different types of Sensors, we will first take a look at a simple example of an automated system, which is possible because of Sensors (and many other components as well).

Real Time Application of Sensors

The example we are talking about here is the Autopilot System in aircrafts. Almost all civilian and military aircrafts have the feature of Automatic Flight Control system or sometimes called as Autopilot.

An Automatic Flight Control System consists of several sensors for various tasks like speed control, height monitoring, position tracking, status of doors, obstacle detection, fuel level, maneuvering and many more. A Computer takes data from all these sensors and processes them by comparing them with pre-designed values.

The computer then provides control signals to different parts like engines, flaps, rudders, motors etc. that help in a smooth flight. The combination of Sensors, Computers and Mechanics makes it possible to run the plane in Autopilot Mode.

All the parameters i.e., the Sensors (which give inputs to the Computers), the Computers (the brains of the system) and the mechanics (the outputs of the system like engines and motors) are equally important in building a successful automated system.

This is an extremely simplified version of Flight Control System. In fact, there are hundreds of individual control systems which preform unique tasks for a safe and smooth journey.

But in this tutorial, we will be concentrating on the Sensors part of a system and look at different concepts associated with Sensors (like types, characteristics, classification etc.).

What is a Sensor?

There are numerous definitions as to what a sensor is but I would like to define a Sensor as an input device which provides an output (signal) with respect to a specific physical quantity (input).

The term “input device” in the definition of a Sensor means that it is part of a bigger system which provides input to a main control system (like a Processor or a Microcontroller).

Another unique definition of a Sensor is as follows: It is a device that converts signals from one energy domain to electrical domain. The definition of the Sensor can be better understood if we take an example in to consideration.

The simplest example of a sensor is an LDR or a Light Dependent Resistor. It is a device, whose resistance varies according to intensity of light it is subjected to. When the light falling on an LDR is more, its resistance becomes very less and when the light is less, well, the resistance of the LDR becomes very high.

We can connect this LDR in a voltage divider (along with other resistor) and check the voltage drop across the LDR. This voltage can be calibrated to the amount of light falling on the LDR. Hence, a Light Sensor.

Now that we have seen what a sensor is, we will proceed further with the classification of Sensors.

Classification of Sensors

There are several classifications of sensors made by different authors and experts. Some are very simple and some are very complex. The following classification of sensors may already be used by an expert in the subject but this is a very simple classification of sensors.

In the first classification of the sensors, they are divided in to Active and Passive. Active Sensors are those which require an external excitation signal or a power signal.

Passive Sensors, on the other hand, do not require any external power signal and directly generates output response.

The other type of classification is based on the means of detection used in the sensor. Some of the means of detection are Electric, Biological, Chemical, Radioactive etc.

The next classification is based on conversion phenomenon i.e., the input and the output. Some of the common conversion phenomena are Photoelectric, Thermoelectric, Electrochemical, Electromagnetic, Thermooptic, etc.

The final classification of the sensors are Analog and Digital Sensors. Analog Sensors produce an analog output i.e., a continuous output signal (usually voltage but sometimes other quantities like Resistance etc.) with respect to the quantity being measured.

Digital Sensors, in contrast to Analog Sensors, work with discrete or digital data. The data in digital sensors, which is used for conversion and transmission, is digital in nature.

Different Types of Sensors

The following is a list of different types of sensors that are commonly used in various applications. All these sensors are used for measuring one of the physical properties like Temperature, Resistance, Capacitance, Conduction, Heat Transfer etc.

1. Temperature Sensor
2. Proximity Sensor
3. Accelerometer
4. IR Sensor (Infrared Sensor)
5. Pressure Sensor
6. Light Sensor
7. Ultrasonic Sensor
8. Smoke, Gas and Alcohol Sensor
9. Touch Sensor
10. Color Sensor
11. Humidity Sensor
12. Position Sensor
13. Magnetic Sensor (Hall Effect Sensor)
14. Microphone (Sound Sensor)
15. Tilt Sensor
16. Flow and Level Sensor
17. PIR Sensor
18. Touch Sensor
19. Strain and Weight Sensor

We will see about few of the above-mentioned sensors in brief. More information about the sensors will be added subsequently. A list of projects using the above sensors is given at the end of the page.

Temperature Sensor

One of the most common and most popular sensors is the Temperature Sensor. A Temperature Sensor, as the name suggests, senses the temperature i.e., it measures the changes in the temperature.

There are different types of Temperature Sensors like Temperature Sensor ICs (like LM35, DS18B20), Thermistors, Thermocouples, RTD (Resistive Temperature Devices), etc.

Temperature Sensors can be analog or digital. In an Analog Temperature Sensor, the changes in the Temperature correspond to change in its physical property like resistance or voltage. LM35 is a classic Analog Temperature Sensor.

Coming to the Digital Temperature Sensor, the output is a discrete digital value (usually, some numerical data after converting analog value to digital value). DS18B20 is a simple Digital Temperature Sensor.

Temperature Sensors are used everywhere like computers, mobile phones, automobiles, air conditioning systems, industries etc.

A simple project using LM35 (Celsius Scale Temperature Sensor) is implemented in this project: TEMPERATURE CONTROLLED SYSTEM.

Proximity Sensors

A Proximity Sensor is a non-contact type sensor that detects the presence of an object. Proximity Sensors can be implemented using different techniques like Optical (like Infrared or Laser), Sound (Ultrasonic), Magnetic (Hall Effect), Capacitive, etc.

Some of the applications of Proximity Sensors are Mobile Phones, Cars (Parking Sensors), industries (object alignment), Ground Proximity in Aircrafts, etc.

Proximity Sensor in Reverse Parking is implemented in this Project: REVERSE PARKING SENSOR CIRCUIT.

Infrared Sensor (IR Sensor)

IR Sensors or Infrared Sensor are light based sensor that are used in various applications like Proximity and Object Detection. IR Sensors are used as proximity sensors in almost all mobile phones.

There are two types of Infrared or IR Sensors: Transmissive Type and Reflective Type. In Transmissive Type IR Sensor, the IR Transmitter (usually an IR LED) and the IR Detector (usually a Photo Diode) are positioned facing each other so that when an object passes between them, the sensor detects the object.

The other type of IR Sensor is a Reflective Type IR Sensor. In this, the transmitter and the detector are positioned adjacent to each other facing the object. When an object comes in front of the sensor, the infrared light from the IR Transmitter is reflected from the object and is detected by the IR Receiver and thus the sensor detects the object.

Different applications where IR Sensor is implemented are Mobile Phones, Robots, Industrial assembly, automobiles etc.

A small project, where IR Sensors are used to turn on street lights: STREET LIGHTS USING IR SENSORS.

Ultrasonic Sensor

An Ultrasonic Sensor is a non-contact type device that can be used to measure distance as well as velocity of an object. An Ultrasonic Sensor works based on the properties of the sound waves with frequency greater than that of the human audible range.

Using the time of flight of the sound wave, an Ultrasonic Sensor can measure the distance of the object (similar to SONAR). The Doppler Shift property of the sound wave is used to measure the velocity of an object.

Arduino based Range Finder is a simple project using Ultrasonic Sensor: PORTABLE ULTRASONIC RANGE METER.

Light Sensor

Sometimes also known as Photo Sensors, Light Sensors are one of the important sensors. A simple Light Sensor available today is the Light Dependent Resistor or LDR. The property of LDR is that its resistance is inversely proportional to the intensity of the ambient light i.e., when the intensity of light increases, its resistance decreases and vise-versa.

By using LDR is a circuit, we can calibrate the changes in its resistance to measure the intensity of Light. There are two other Light Sensors (or Photo Sensors) which are often used in complex electronic system design. They are Photo Diode and Photo Transistor. All these are Analog Sensors.

There are also Digital Light Sensors like BH1750, TSL2561, etc., which can calculate intensity of light and provide a digital equivalent value.

Check out this simple LIGHT DETECTOR USING LDR project.

Smoke and Gas Sensors

One of the very useful sensors in safety related applications are Smoke and Gas Sensors. Almost all offices and industries are equipped with several smoke detectors, which detect any smoke (due to fire) and sound an alarm.

Gas Sensors are more common in laboratories, large scale kitchens and industries. They can detect different gases like LPG, Propane, Butane, Methane (CH4), etc.

Now-a-days, smoke sensors (which often can detect smoke as well gas) are also installed in most homes as a safety measure.

The “MQ” series of sensors are a bunch of cheap sensors for detecting CO, CO2, CH4, Alcohol, Propane, Butane, LPG etc. You can use these sensors to build your own Smoke Sensor Application.

Check out this SMOKE DETECTOR ALARM CIRCUIT without using Arduino.

Alcohol Sensor

As the name suggests, an Alcohol Sensor detects alcohol. Usually, alcohol sensors are used in breathalyzer devices, which determine whether a person is drunk or not. Law enforcement personnel uses breathalyzers to catch drunk-and-drive culprits.

A simple tutorial on HOW TO MAKE ALCOHOL BREATHALYZER CIRCUIT?

Touch Sensor

We do not give much importance to touch sensors but they became an integral part of our life. Whether you know or not, all touch screen devices (Mobile Phones, Tablets, Laptops, etc.) have touch sensors in them. Another common application of touch sensor is trackpads in our laptops.

Touch Sensors, as the name suggests, detect touch of a finger or a stylus. Often touch sensors are classified into Resistive and Capacitive type. Almost all modern touch sensors are of Capacitive Types as they are more accurate and have better signal to noise ratio.

If you want to build an application with Touch Sensor, then there are low-cost modules available and using those touch sensors, you can build TOUCH DIMMER SWITCH CIRCUIT USING ARDUINO.

Color Sensor

A Color Sensor is an useful device in building color sensing applications in the field of image processing, color identification, industrial object tracking etc. The TCS3200 is a simple Color Sensor, which can detect any color and output a square wave proportional to the wavelength of the detected color.

If you are interested in building a Color Sensor Application, checkout this ARDUINO BASED COLOR DETECTOR project.

Humidity Sensor

If you see Weather Monitoring Systems, they often provide temperature as well as humidity data. So, measuring humidity is an important task in many applications and Humidity Sensors help us in achieving this.

Often all humidity sensors measure relative humidity (a ratio of water content in air to maximum potential of air to hold water). Since relative humidity is dependent on temperature of air, almost all Humidity Sensors can also measure Temperature.

Humidity Sensors are classified into Capacitive Type, Resistive Type and Thermal Conductive Type. DHT11 and DHT22 are two of the frequently used Humidity Sensors in DIY Community (the former is a resistive type while the latter is capacitive type).

Checkout this tutorial with DHT11 HUMIDITY SENSOR ON ARDUINO.

Tilt Sensor

Often used to detect inclination or orientation, Tilt Sensors are one of the simplest and inexpensive sensors out there. Previously, tilt sensors are made up of Mercury (and hence they are sometimes called as Mercury Switches) but most modern tilt sensors contain a roller ball.

A simple Arduino based title switch using tilt sensor is implemented here HOW TO MAKE A TILT SENSOR WITH ARDUINO?

In this article, we have seen about What is a Sensor, what are the classification of sensors and Different Types of Sensors along with their practical applications. In the future, I will update this article with more sensors and their applications.

The post What is a Sensor? Different Types of Sensors and their Applications appeared first on ElectronicsHub.

The use of switching devices like transistors give rise to a special case of the Boolean algebra called as switching algebra. In switching algebra, all the variables assume one of the two values which are 0 and 1.

In Boolean algebra, 0 is used to represent the ‘open’ state or ‘false’ state of logic gate. Similarly, 1 is used to represent the ‘closed’ state or ‘true’ state of logic gate.

A Boolean expression is an expression which consists of variables, constants (0-false and 1-true) and logical operators which results in true or false.

A Boolean function is an algebraic form of Boolean expression. A Boolean function of n-variables is represented by f(x1, x2, x3….xn). By using Boolean laws and theorems, we can simplify the Boolean functions of digital circuits. A brief note of different ways of representing a Boolean function is shown below.

• Sum-of-Products (SOP) Form
• Product-of-sums (POS) form
• Canonical forms

There are two types of canonical forms:

• Sum-of-min terms or Canonical SOP
• Product-of- max terms or Canonical POS

Boolean functions can be represented by using NAND gates and also by using K-map (Karnaugh map) method. We can standardize the Boolean expressions by using by two standard forms.

SOP form – Sum Of Products form

POS form – Product Of Sums form

Standardization of Boolean equations will make the implementation, evolution and simplification easier and more systematic.

Sum of Product (SOP) Form

The sum-of-products (SOP) form is a method (or form) of simplifying the Boolean expressions of logic gates. In this SOP form of Boolean function representation, the variables are operated by AND (product) to form a product term and all these product terms are ORed (summed or added) together to get the final function.

A sum-of-products form can be formed by adding (or summing) two or more product terms using a Boolean addition operation. Here the product terms are defined by using the AND operation and the sum term is defined by using OR operation.

The sum-of-products form is also called as Disjunctive Normal Form as the product terms are ORed together and Disjunction operation is logical OR. Sum-of-products form is also called as Standard SOP.

SOP form representation is most suitable to use them in FPGA (Field Programmable Gate Arrays).

Examples

AB + ABC + CDE

(AB) ̅ + ABC + CD E ̅

SOP form can be obtained by

• Writing an AND term for each input combination, which produces HIGH output.
• Writing the input variables if the value is 1, and write the complement of the variable if its value is 0.
• OR the AND terms to obtain the output function.

Ex: Boolean expression for majority function F = A’BC + AB’C + ABC ‘ + ABC

Truth table:

Now write the input variables combination with high output. F = AB + BC + AC.

Checking

By Idempotence law, we know that

([ABC + ABC)] + ABC) = (ABC + ABC) = ABC

Now the function F = A’BC + AB’C + ABC ‘ + ABC

= A’BC + AB’C + ABC’ + ([ABC + ABC)] + ABC)

= (ABC + ABC ‘) + (ABC + AB’C) + (ABC + A’BC)

= AB (C + C ‘) + A (B + B’) C + (A + A’) BC

= AB + BC + AC.

Product of Sums (POS) Form

The product of sums form is a method (or form) of simplifying the Boolean expressions of logic gates. In this POS form, all the variables are ORed, i.e. written as sums to form sum terms.

All these sum terms are ANDed (multiplied) together to get the product-of-sum form. This form is exactly opposite to the SOP form. So this can also be said as “Dual of SOP form”.

Here the sum terms are defined by using the OR operation and the product term is defined by using AND operation. When two or more sum terms are multiplied by a Boolean OR operation, the resultant output expression will be in the form of product-of-sums form or POS form.

The product-of-sums form is also called as Conjunctive Normal Form as the sum terms are ANDed together and Conjunction operation is logical AND. Product-of-sums form is also called as Standard POS.

Examples

(A+B) * (A + B + C) * (C +D)

(A+B) ̅ * (C + D + E ̅)

POS form can be obtained by

• Writing an OR term for each input combination, which produces LOW output.
• Writing the input variables if the value is 0, and write the complement of the variable if its value is 1.
• AND the OR terms to obtain the output function.

Ex: Boolean expression for majority function F = (A + B + C) (A + B + C ‘) (A + B’ + C) (A’ + B + C)

Now write the input variables combination with high output. F = AB + BC + AC.

Checking

By Idempotence law, we know that

[(A + B + C) (A + B + C)] (A + B + C) = [(A + B + C)] (A + B + C) = (A + B + C)

Now the function

F = (A + B) (B + C) (A + C)

= (A + B + C) (A + B + C ‘) (A + B’ + C) (A’ + B + C)

= [(A + B + C) (A + B + C)] (A + B + C) (A + B + C ‘) (A + B’ + C) (A’ + B + C)

= [(A + B + C) (A + B + C ‘)] [(A + B + C) (A’ + B + C)] [(A + B + C) (A + B’ + C)]

= [(A + B) + (C * C ‘)] [(B + C) + (A * A’)] [(A + C) + (B * B’)]

= [(A + B) + 0] [(B + C) + 0] [(A + C) + 0] = (A + B) (B + C) (A + C)

Canonical Form (Standard SOP and POS Form)

Any Boolean function that is expressed as a sum of minterms or as a product of max terms is said to be in its “canonical form”.

It mainly involves in two Boolean terms, “minterms” and “maxterms”.

When the SOP form of a Boolean expression is in canonical form, then each of its product term is called ‘minterm’. So, the canonical form of sum of products function is also known as “minterm canonical form” or Sum-of-minterms or standard canonical SOP form.

Similarly, when the POS form of a Boolean expression is in canonical form, then each of its sum term is called ‘maxterm’. So, the canonical form of product of sums function is also known as “maxterm canonical form or Product-of sum or standard canonical POS form”.

Min terms

A minterm is defined as the product term of n variables, in which each of the n variables will appear once either in its complemented or un-complemented form. The min term is denoted as mi where i is in the range of 0 ≤ i < 2ⁿ.

A variable is in complemented form, if its value is assigned to 0, and the variable is un-complimented form, if its value is assigned to 1.

For a 2-variable (x and y) Boolean function, the possible minterms are:

x’y’, x’y, xy’ and xy.

For a 3-variable (x, y and z) Boolean function, the possible minterms are:

x’y’z’, x’y’z, x’yz’, x’yz, xy’z’, xy’z, xyz’ and xyz.

• 1 – Minterms = minterms for which the function F = 1.
• 0 – Minterms = minterms for which the function F = 0.

Any Boolean function can be expressed as the sum (OR) of its 1- min terms. The representation of the equation will be

• F(list of variables) = Σ(list of 1-min term indices)

Ex: F (x, y, z) = Σ (3, 5, 6, 7)

The inverse of the function can be expressed as a sum (OR) of its 0- min terms. The representation of the equation will be

• F(list of variables) = Σ(list of 0-min term indices)

Ex: F’ (x, y, z) = Σ (0,1, 2, 4)

Examples of canonical form of sum of products expressions (min term canonical form):

i) Z = XY + XZ′

ii) F = XYZ′ + X′YZ + X′YZ′ + XY′Z + XYZ

In standard SOP form, the maximum possible product terms for n number of variables are given by 2ⁿ. So, for 2 variable equations, the product terms are 22 = 4. Similarly, for 3 variable equations, the product terms are 23 = 8.

Max terms

A max term is defined as the product of n variables, within the range of 0 ≤ i < 2ⁿ. The max term is denoted as Mi. In max term, each variable is complimented, if its value is assigned to 1, and each variable is un-complimented if its value is assigned to 0.

For a 2-variable (x and y) Boolean function, the possible max terms are:

x + y, x + y’, x’ + y and x’ + y’.

For a 3-variable (x, y and z) Boolean function, the possible maxterms are:

x + y + z, x + y + z’, x + y’ + z, x + y’ + z’, x’ + y + z, x’ + y + z’, x’ + y’ + z and x’ + y’ + z’.

• 1 – Max terms = max terms for which the function F = 1.
• 0 – max terms = max terms for which the function F = 0.

Any Boolean function can be expressed the product (AND) of its 0 – max terms. The representation of the equation will be

• F(list of variables) = Π (list of 0-max term indices)

Ex: F (x, y, z) = Π (0, 1, 2, 4)

The inverse of the function can be expressed as a product (AND) of its 1 – max terms. The representation of the equation will be

• F(list of variables) = Π (list of 1-max term indices)

Ex: F’ (x, y, z) = Π (3, 5, 6, 7)

Examples of canonical form of product of sums expressions (max term canonical form):

i. Z = (X + Y) (X + Y′)

ii. F = (X′ + Y + Z′) (X′ + Y + Z) (X′ + Y′ + Z′)

In standard POS form, the maximum possible sum terms for n number of variables are given by 2ⁿ. So, for 2 variable equations, the sum terms are 22 = 4. Similarly, for 3 variable equations, the sum terms are 23 = 8.

Table for 2n min terms and 2n max terms

The below table will make you understand about the representation of the mean terms and max terms of 3 variables.

Conversions of Canonical Forms

We can represent the one canonical formed equation in other canonical form i.e. we can represent the SOP form of equation in POS form and POS form equation in SOP form. To convert the canonical equations, we interchange the Σ and Π symbols after listing out the index numbers of the equations, which are excluded from the original form of equation.

The important thing to remember about Boolean functions is that, the SOP and POS forms are Duals to each other. There are 2 steps to follow to convert the canonical form of the equations. They are

Step 1: Interchanging the operational symbols, Σ and Π in the equation.

Step 2: Use the De Morgan’s principle of Duality to the index numbers of the Boolean function or writing the indexes of the terms that are not presented in the given form of equation.

Conversion of SOP form to POS form

To convert the SOP form into POS form, first we should change the Σ to Π and then write the numeric indexes of missing variables of the given Boolean function.

Example:

The SOP function

F = ∑ A, B, C (0, 2, 3, 5, 7) = A’ B’ C’ + A B’ C’ + A B’ C + ABC’ + ABC  is written in POS form by

Step 1: changing the operational sign to Π

Step 2: writing the missing indexes of the terms, 001, 100 and 110. Now write the sum form for these noted terms.

001 = (A + B + C) 100 = (A + B’ + C’) 110 = (A + B’ + C’)

Writing down the new equation in the form of POS form,

F = Π A, B, C (1, 4, 6) = (A + B + C) * (A + B’ + C’) * (A + B’ + C’)

Conversion of POS form to SOP form

To convert the POS form into SOP form, first we should change the Π to Σ and then write the numeric indexes of missing variables of the given Boolean function.

Ex: The POS function F = Π A, B, C (2, 3, 5) = A B’ C’ + A B’ C + ABC’ is written in SOP form by

Step 1: changing the operational sign to Σ

Step 2: writing the missing indexes of the terms, 000, 001, 100, 110, and 111. Now write the product form for these noted terms.

000 = A’ * B’ * C’ 001 = A’ * B’ * C 100 = A * B’ * C’

110 = A * B* C’ 111 = A * B * C

Writing down the new equation in the form of SOP form,

F = Σ A, B, C (0, 1, 4, 6, 7) = (A’ * B’ * C’) + (A’ * B’ * C) + (A * B’ * C’) + (A * B* C’) + (A * B * C)

Conversion of SOP form to standard SOP form or Canonical SOP form

We can include all the variables in each product term of the SOP form equation, which doesn’t have all the variables by converting into standard SOP form. The normal SOP form function can be converted to standard SOP form by using the Boolean algebraic law, (A + A’ = 1) and by following the below steps.

Step 1:

By multiplying each non-standard product term with the sum of its missing variable and its complement, which results in 2 product terms

Step 2:

By repeating the step 1, until all resulting product terms contain all variables

By these two steps we can convert the SOP function into standard SOP function. In this process, for each missing variable in the function, the number of product terms will double.

Example:

Convert the non standard SOP function F = x y + x z + y z

Sol:

F = x y + x z + y z

= x y (z + z’) + x (y + y’) z + (x + x’) y z

= x y z + x y z’ + x y z + x y’ z + x y z + x’ y z

= x y z + x y z’ + x y’ z + x’ y z

The standard SOP form is F = x y z + x y z’ + x y’ z + x’ y z

Conversion of POS form to standard POS form or Canonical POS form

We can include all the variables in each product term of the POS form equation, which doesn’t have all the variables by converting into standard POS form. The normal POS form function can be converted to standard POS form by using the Boolean algebraic law, (A * A’ = 0) and by following the below steps.

Step 1:

By adding each non-standard sum term to the product of its missing variable and its complement, which results in 2 sum terms

Step 2:

Applying Boolean algebraic law, A + BC = (A + B) * (A + C)

Step 3:

By repeating the step 1, until all resulting sum terms contain all variables

By these three steps we can convert the POS function into standard POS function.

Example:

F = (A’ + B + C) * (B’ + C + D’) * (A + B’ + C’ + D)

In the first term, the variable D or D’ is missing, so we add D*D’ = 1 to it. Then

(A’ + B + C + D*D’) = (A’ + B + C + D) * (A’ + B + C + D’)

Similarly, in the second term, the variable A or A’ is missing, so we add A*A’ = 1 to it. Then

(B’ + C + D’ + A*A’) = (A + B’ + C + D’) * (A’ + B’ + C + D’)

The third term is already in the standard form, as it has all the variables. Now the standard POS form equation of the function is

F = (A’ + B + C + D) * (A’ + B + C + D’) * (A + B’ + C + D’) * (A’ + B’ + C + D’) * (A + B’ + C’ + D)

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