Finding Collector, Emitter and Base Pins of a Transistor

I would have Written complete post on How to Find the Collector, Emitter and Base Pins of the Transistor but i am Writing this as a specific post for those holding Arduino. They can determine the Pins of a Transistor using Arduino easily.

Hardware Required

  • Arduino
  • Transistor (to be Tested)
  • LED or Motor
  • BreadBoard (Optional)
  • Jumper wire or Hook Up Wire (Optional)


Before Proceeding You Should Know what is Transistor? It is Semiconducting Device which is commonly used as Amplifier or a Switch and has many wide Applications in the Industry. A bipolar Junction transistor has three Pins Collector, Base, Emitter. While working it is easy to Identify the Base pin as it is in the Middle. But How will you Find the other ones?

We will use the Transistor as a Switch to determine the other pins. Look How.

Circuit Diagram

As you see in the above Picture, One Pin is Connected to the the Positive End of the Battery. There other end you may connect to the Positive Leg of the LED or to the Motor. But you should Take care that the other end of the whichever Component you are using must be connected to the Negative End of the Battery. The BASE pin must be connected to the Arduino and should be given HIGH signal.

If the LED Glows then the End to which Battery connected is the Collector Pin, and the end to which Led is connected is the Emitter Pin.

If the LED fails to glow or the motor Didn’t Run then The End to which LED is Connected is Collector End and the End to which Battery is Connected is the Emitter End.

The Basic Working Behind is that when a small amount of current flows through the BASE then it completes the circuit between the Collecter and Emmiter, f the Collecter is at High Voltage then the Current Flows from Collector to the Emmiter so the LED Glows.