Cheap ULN2803A Motor Driver

Normally, a PIC or other chip can't output enough current and/or voltage to drive a DC motor, and if the DC motor you need to control requires 500ma current or less, or if it requires more more than 5vdc power, here's a cheap way to drive it. A typical, small hobby motor that needs 3, 5, 7, 9 or 12vdc is an example. To start, here's an outline of connections to the ULN2803A. Note: A ULN2804A is a drop-in, "high-current" version of the ULN2803A.

And here's how you'd connect your computer or controller to it, using input #1 as an example:

Here's an example of one compact driver design that was made on an experimenter's breadboard. This includes header pins for connecting Dupont cables, and the short row of 4 pins at the end of the chip are common to each other, making for an easy way to connect multiple grounds.

Additional information:

• Any controller's PIC that outputs a positive control signal should work.
• The ULN2803A could conceivably control up to 8 motors, depending on their current draw (total < 500ma)
• Multiple inputs and outputs can be chained together for more current capacity. The total dissipation of the ULN2803A chip is slightly more than 2 watts.
• The motor speed can also be controlled further by using common PWM in the +v control signal.
• The ULN2803A has a maximum voltage rating of 50vdc.