Introduction

A transistor is a semiconductor device used to amplify and switch electronic signals. It is made of a solid piece of semiconductor material, with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current flowing through another pair of terminals. Because the controlled (output) power can be much more than the controlling (input) power, the transistor provides amplification of a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits. The transistor is the fundamental building block of modern electronic devices, and is ubiquitous in modern electronic systems. Following its release in the early 1950s the transistor revolutionized the field of electronics, and paved the way for smaller and cheaper radios, calculators, and computers, amongst other things.

Some transistors :



















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Steady Hand Game 2

Handle ring is connected to +ve of battery. When ring is moving through the wire and it touched on the wire then the red led glow and C1 charges. C maintain this glow for some time. This also keep the T1 turn off. If handle ring reached the end not touching wire the T1 turn on and green LED turn on with C.

Reminder

When the reset button presses the capacitor charges fully. Then the positive charge comes to the base of T, through VR ad T1 turns off. This state sustain till the capacitor discharges. This interval is controlled by VR. using this we set the time. To stop the reminder we discharge the capacitor totally. When the capacitor discharge, T turn on and led glows.

Amplifier

When we connect IC Um 66 to Battery and speaker a small sound is produced.
When we connect a transistor with the output of ic um 66 the sound increases 2 times. Here transistor is used as an amplifier.

Steady Hand Game

Needle is connected to +ve of battery. When needle is moving through the ring and it touched on the ring then the red led glow and C1 charges and the game is over. C maintain this glow for some time. This also keep the T1 turn off. If needle touched on metal surface not touching ring the T1 switch on and green LED turn on with C, then you won the game.

Burglar Alarm

From transmitter the laser light is produced. Place the transmitter and receiver so that the laser beam fall on LDR. When laser falls on LDR this turns off t1. When the beam split by a tress passer or burglar LDR stops conducting and t1 turns on and LED glows. C store Voltage and Maintains this glow.

Water Level Indicater

Connect the metal pins on the water tank as one at the bottom, one at the minimum level , one at maximum level and last one at the point at which the water will overflow.
Pin A is connected to +ve of battery.3 LED are showing the amount of water in the tank
The red LED(low) will be always on.

The fact is that the water is a conductor. If the level of water is between C and B, +ve charge from A will pass through B. In this way the base of t2 gets +ve charge and t2 turn on.this will turn on green led.

When the water reaches B t2 turns on and Orange LED glows.

If Water level is lower than B the t3 turn on and the siren for low water level makes sound.

If water reaches D then the t4 switches the siren for high water level.

This will be very useful to every houses.

Piano

The transistors BC 548(T2), BC 188(T1), and capacitor 0.01(C1) muF makes an oscillation circuit and makes a continues vibration on the speaker coil. The frequency of the vibration is depended on the resistance given to the base of T2. This vibration becomes a sound of corresponding frequency. Through the switches the resistance is given in particular value and this creates different sounds.
Here transistor is used for oscillation.

Emergency

When electricity is available transformer will provide 6v output. This passes through diode and charges battery. But the (+)ve charge from transformer turn off PNP transistor and light don’t glow.
When electricity is not available PNP transistor switches and LED glows from the battery power.

This circuit acts as an emergency light. Here the switching capability of transistor is used.

Automatic Night Light

The LDR in this circuit must be placed outdoor. At day time the light falls on LDR. (+)ve charge reaches the transistor's base through LDR. There will be more (+)ve charge than (–)ve charge at transister’s base.
So t1 turn off. And LED doesn’t glow .

At night LDR doesn’t transfer (+)ve Charge. So there will be more (+)ve charge than (–)ve charge at transistor's base. So the transistor, turns on and LED glows

Through these operations the LED glow at night and doesn't glow at day.