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I want to power a small motor with a 9V battery and control it with PWM using an Arduino Leonardo. I know I can power the motor separately, but this introduces the problem of needing a battery to power the motor (9V battery) and another power source to power the Arduino (another 9V battery?)

Would it be safe to simply power the Arduino with a 9V battery and use the Vin pin on the board (which is unregulated and outputs directly the power source powering the Arduino) to drive the motor? That way, I power everything from the 9V battery, and use a transistor to drive the motor.

Thanks a lot!

Steve.

  • That should work. But you may have a problem with the small capacity of 5V battery, compared to AA or even AAA 1.5V batteries. I don't think that will be enough to drive a motor. – jfpoilpret May 20 '14 at 10:50
  • I will probably use a couple of AA instead. I'll calculate which type of batteries would be optimal for my project. – Steve May 20 '14 at 17:25
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If you use a transistor circuit as shown below, back EMF would not cause any trouble. enter image description here

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Yes it is OK to do that. But the thing you should consider in mind is "What is the current requirement of the motor?"

You say

I want to motor a small motor with a 9V battery and control it with PWM

This means you have a servo motor, which might require a lot of current depending on the torque. So if you have a battery with low 'mAh', your battery will dry out very quickly. This might or might not be a problem for you depending on your requirements.

  • Woops I meant "drve a motor". It's actually not a servo but just a simple motor harvested from an old cd changer. I am aware that a 9V battery might not provide a very good battery life, but that is not my priority for now. As long as it works and is reliable all is good for now. – Steve May 20 '14 at 6:18
  • in that case, it would work just fine. – Damon May 20 '14 at 6:20
  • You also need to ensure that the Arduino you use has a voltage regulator. Not all of them do. – Phil May 20 '14 at 7:50
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The arduino has its on voltage regulator, so feeing 9v to the arduino is not a problem. But the arduino will not drive the motor directly. You need to use a transistor big enough to hundle the amperage of your motor (e.g.tip120). The diagram above is a good indication of how to connect it. Yet the diagram is missing a diode (1n4001 or 1n4004) from the GnD to Vcc, as to avoid back voltage from the motor, which may damage your arduino.

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