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The ULN2004 Transistor array is useful for driving unipolar stepper motors or your application requires multiple transistors.
Here are the parts you will need:
The ULN2004 transistor array contains seven npn transistors. There are seven inputs, seven corresponding outputs, ground and a power.
The outputs connect to the cathode (ground) of the component you are controlling.
To test the transistor array: Connect a wire from your microcontroller to pin A1 Connect the cathode(ground) of an LED to pin B1 Connect the anode(power) of the led to power Connect power and ground pins.
Your code should send a digital HIGH to pin A1 and the light will go on.
For the other pins, repeat the procedure for pins A2, B2, A3, B3 and so on.