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Easy, Reversible Motor Control for Arduino (or any Microcontroller)

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Step 10: Connect Resistors

Picture of Connect Resistors
Trim the leads of two 220 Ohm resistors to about 1/4 inch using scissors.

Solder a resistor to the end of the right-most pin of each TIP120 as pictured.

These resistors are connected to the Base of the transistors.  They limit current flow between the transistors and your microcontroller to safe levels.