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I'm successfully running a stepper from my Arduino via a ULN2003A and a secondary power supply. It uses the first four of the seven Darlington Pairs on the chip, leaving three spare.

A) Is there any reason I wouldn't be able to use one of the remaining pairs to drive a standard DC hobby motor? (For the sake of helping future visitors .. what about running three motors off the remaining three pairs?)

B) Do I need anything other than to connect the motor to the chip? (The chip's board has LEDs and resistors on each of pins 1 - 4, but I don't believe they're in series and thus my guess is they can be left off.)

C) The DC motor is on a PWM Pin. Is that the correct way to control its speed?

The image attached shows the setup in case I haven't been clear.

enter image description here

(I could probably just build it and see, but I'm new to Arduino and still scared of the blue smoke if I get something wrong!)

  • Low karma on this SE. Suggest adding tags: "ULN2003A" and "Darlington" – RickMeasham Nov 17 '14 at 3:21
  • Is the COM connection of the chip available anywhere? – Ignacio Vazquez-Abrams Nov 17 '14 at 13:51
  • @IgnacioVazquez-Abrams: Yes, I believe the COM of the chip is the GND pin where the black wire connects it to the negative rail – RickMeasham Nov 18 '14 at 4:42
  • I hope not, because that's not what it's for at all. – Ignacio Vazquez-Abrams Nov 18 '14 at 4:44
  • Also, what piece is that and why aren't you using a schematic? – Ignacio Vazquez-Abrams Nov 18 '14 at 4:45
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Should work just fine. But you'd have to connect the motor to the positive rail, and since the ULN2003 can only sink current.

Normally when connecting a motor, you'd add a flyback diode. But the ULN2003 already has those inside the chip.

PWM is the easiest way to (somewhat) control the speed of a DC motor.

| improve this answer | |
  • So I should just move the black wire connecting the yellow side of the motor from the ground to the positive? – RickMeasham Nov 18 '14 at 1:21
  • Yes, assuming the motor isn't polar. (otherwise, purple to positive, black to the ULN2003) – Gerben Nov 18 '14 at 16:24

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