BOARDS :

CLASSIFICATION :

1) PROJECT BOARD.2) VARRO BOARD3) COPPER LAMINATED BOARD4) PRINTED CIRCUIT BOARD(PCB)

PROJECT BOARD.It is a reusable solderless device used to build a prototype of an electronic circuit and for experimenting with circuit designs.

Fig: Project board fig:Varro board

VARRO BOARD:

It is sholderable designer board where the designer test the designed circuit before marketing his product.

COPPER LAMINATED BOARD:

It is the board where the copper foil is laminated over the base material.

The standard thickness of copper in the copper laminated board is about 105 µm.

COPPER LAMINATED BOARDFIG: PCB

1. THE IDEAL RESISTOR:

In an ideal resistor, the resistance remains constant regardless of the applied voltage or current flowing through the device or the rate of change of the current.

Feature:

1) Ideal resistors are used in the circuit where the exact value of resistance is required.

2) They are very reliable because they do not change their values when subjected to changing temperature and other environmental factors.

2. FIXED RESISTORS:

The fixed resistors have two terminals.The most common of the low wattage, fixed-type resistors is the molded-carbon composition resistor. The resistive material is of carbon-clay composition. The leads are made of tinned copper.

Feature:1) Resistors of these are readily available values ranging from few

ohms to about 22 MΩ, having a tolerance range of 5 -20%.2) They are quit inexpensive. 3) The relative sizes of all fixed resistors change with the wattage

rating. The size increased for increased wattage rating in order to withstand the higher currents and dissipation losses.

Fig: fixed resistor

3. VARIABLE RESISTOR:

The variable resistor is a resistor whose value can be adjusted by turning a shaft or sliding a control. These are also called

POTENTIOMETERS or RHEOSTATS and allow the resistance of the device to be altered by hand.

RHEOSTAT: A variable resistor with two terminals, one fixed and one sliding. It is often used with high currents.

POTENTIOMETER: a common type of variable resistor. One common use is as volume controls on audio amplifiers and other forms of amplifier.

APPLICATIONS

1) Potentiometers are very widely used as a part of displacement transducers because of the simplicity of construction and because they can give a large output signal.

2) One of the most common uses for modern low-power potentiometers is as audio control devices. Both faders and rotary potentiometers are regularly used to adjust loudness, frequency attenuation and other characteristics of audio signals.

3) A potentiometer used in combination with an inductor or capacitor acts as a "tone" control.

.

Fig: Rheostat Fig: Potentiometer

4. SPRING RESISTOR:Use two springs connected by soldering material. When subjected to high voltage the soldered material malts and disconnects the component.

Fig: Spring resistor

APPLICATION:1) They are used to protect the components in circuit from extra

high voltage by disconnect its conducting springs.

5. WIRE WOUND RESISTOR:A wire wound resistor uses a length of resistance wire. The wire is wound onto a round, hollow porcelain core. The end of the winding are attached to these metal pieces.Commonly available wire wound resistors have resistance values ranging from 1Ω to 100 kΩ and wattage ratings up to about 200 W.

Fig: WIRE WOUND

RESISTOR

APPLICATIONS: Loading Resistors Dynamic Braking Resistors Starting Resistors Neutral Grounding Resistors

6. GENERAL PURPOSE RESISTOR:

This types of resistors are used in all general porpose equipments . Usually they are chip and are of many shapes.

APPLICATIONS:

1) Used for Biasing in electronics is the method of establishing predetermined voltages and/or currents at various points of a circuit).

2) Used for voltage dividing (voitagedivider is a simple device designed to create a voltage (Vout) which is proportional to another voltage (Vin).)

7. SAFETY RESISTOR:

They are used to protect the expensive components used in circuit.

They tolerate voltage within a range but when the voltage go out the desired level then safety resistor radically increase its value and restrict the effect of high voltage. They have Excellent Reliability and Stability.

APPLICATION:

1) Use only for protection purpose.

8. FUSIBLE RESISTOR:

They employ the strategy of fuse off when over current is passed through.

SYMBOL OF FUSIBLE RESISTOR:

APPLICATIONS:

Use only for protection purpose.

FUSIBLE RESISTOR

9. THERMISTOR:

A thermistor is a temperature-dependent resistor.

SYMBOL OF THERMISTOR:

APPLICATIONS:1) A thermistor is a type of resistor used to measure temperature

changes,2) thermistors can be used as current-limiting devices for circuit

protection, as replacements for fuses

10.POSISTOR:ΔR = kΔT

In this equation if k is positive, the resistance increases with increasing temperature, and the device is called Posistor.

SYMBOL OF POSISTOR:

APPLICATIONS:1) PTC thermistors can be used as heating elements in small

temperature-controlled ovens.

11. SENSISTOR:

SENSISTOR (detectors) are that react to environmental conditions .

SYMBOL OF SENSISTOR:

12.VARISTOR:

A varistor is an electronic component with a significant non-ohmic current-voltage characteristic. A varistor is also known as Voltage Dependent Resistor or VDR.

APPLICATIONS:

1) varistor are often used to protect circuits against excessive transient voltages.

2) they will shunt the current created by the high voltage away from the sensitive components.

For example, follow-through current as a result of a lightning strike may generate excessive current and varistor becomes short to protect components.

13 LIGHT DEPANDENT RESISTOR (LDR):

A photoresistor or LDR is an electronic component whose resistance changes with changing incident light intensity. It can also be referred to as a light-dependent resistor (LDR), photoconductor, or photocell.

So--lots of light = lots of conductivity: less light = less conductivity.

Circuit symbol

APPLICATIONS:

Applications include: auto-focus lenses, exposure meters, contrast controls for TVs, dimmer or light switches, flame detectors, electronic toys, street lamp switches, optocouplers.

14 FLAME PROOF RESISTOR:

they are usually used for protection purpose.