In this tutorial, you’ll learn how to control a high-current DC load such as a DC motor or an incandescent light from a microcontroller.
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Connect a transistor to the microcontroller
The transistor allows you to control a circuit that’s carrying higher current and voltage from the microcontroller. It acts as an electronic switch. The one you’re using for this lab is an NPN-type transistor called a TIP120. The datasheet for it can be found here. It’s designed for switching high-current loads. It has three connections, the base, the collector, and the emitter. The base is connected to the microcontroller’s output. The high-current load (i.e. the motor or light) is attached to its power source, and then to the collector of the transistor. The emitter of the transistor is connected to ground.
Pinout of a TIP-120 transistor, from left to right: base, collector, emitter.
Note: you can also use an IRF510 or IRF520 MOSFET transistor for this. They have the same pin configuration as the TIP120, and perform similarly. They can handle more amperage and voltage, but are more sensitive to static electricity damage.
The schematic symbol of an NPN transistor where B is the base, C is the collector, and E is the emitter.
Connect the base to an output pin of the microcontroller, and the emitter to ground like so:
Connect a motor and power supply
Attach a DC motor to the collector of the transistor. Most motors will require more amperage than the microcontroller can supply, so you will need to add a separate power supply as well. If your motor runs on around 9V, you could use a 9V battery. A 5V motor might run on 4 AA batteries. a 12V battery may need a 12V wall wart, or a 12V battery. The ground of the motor power supply should connect to the ground of the microcontroller, on the breadboard.
For more details: Uing a transistor to control high current loads with an Arduino