1 Transistor

2 Transistors are used to turn components on and off They come in all different shapes and sizes

3 Purpose To turn components on and off we could use the Arduino digital pins

4 Purpose To turn components on and off we could use the Arduino digital pins However, they only output 5V and 20mA, about enough to light up an LED

5 How it works Suppose we wanted to operate the LED on the left, with its switch and 12V supply But instead of a manual switch, we can have an Arduino “flip” a transistor In the diagram on the right a transistor has replaced the switch By sending a small amount of current through A, we allow a large amount to flow from B to C 12V

6 Wiring We can trace the circuit for the DC motor on the right A – power into red bar B – into the motor C – out of the motor D – into the transistor E – out of the transistor F – back into ground

7 Wiring Note how the transistor is an integral part of the circuit It is acting as the switch The third leg is called the “gate”, and is used to “operate the switch”

8 Wiring Connect the gate to an Arduino pin digitalWrite HIGH = ON digitalWrite LOW = OFF A pull down resistor connected to ground is needed to turn the switch off when the Arduino pin is LOW

9 LAB Complete the Transistor lab in Unit 11 of your textbook