A quick circuit showing how to control the speed of a DC motor with a potentiometer with your Arduino board. Also shows how to use a TIP120 transistor to allow the Arduino control a larger power supply.
Transistors are 3 pin devices, which via the 3rd pin (Base) allow it to control the current passing through the other 2 pins (Collector and Emitter). So for this tutorial I am using the power from the Arduino Digital PWM pin 9 (+5V) to control the flow of current to a DC motor which uses an additional power supply with a much larger current than the Arduino board can supply or control. Of course like most electrical components each transistor is designed for a specfic operating range or current.
Below you can see TIP120 the pins and how they appear in a schematic:
So thats the transistor. Next up is the rectifier diode, I’m using this inbetween the power supply flowing from the motor. It acts like a one way valve to only allow the current to flow one way, so my circuit should be protected should the motor power supply cause a surge or if the motor draws too much current. The main thing to remember is that Diodes like LED’s have a correct orientation, shown to the left.
The other item is the potentiometer, which is basically a variable resistor. By turning it you control the flow of current by allowing more or less through. Potentiometers, like resistors have a resistance rating in Ohms and a power rating. For this I am using a pot with a 10K ohm rating.
Arduino TIP120 Circuit Components
1K Ohm resistor (Brown, Black, Red, Gold)
1n4004 1A Diode
6V DC motor
Arduino Deumilanove w/ ATMEGA328
Breadboard / Prototyping board
Jumper/ Connector wires
4x AA battery holder
4x AA batteries
Optional 9V DCpower supply or use the USB power for the Arduino
TIP120 Arduino DC Motor Control Circuit
Pretty simple, but remember that the GND connection must be shared between the Arduino and the additional power supply and I’m using a 1k Ohm resistor between Arduino pin 9 and the Base pin of the transistor.