I have a motor hooked up to the emitter of a NTE24 transistor and ground, the collector is hooked up to 3.7V, and the base is connected through a 10ohm resistor to a PWM pin on an arduino mega, which is powered by 3.7V through Vin. I use analogwrite on the pin to control the motor speed.

When i turn it on, the arduino just resets. I think it’s because the base is drawing too much current from the arduino pwm pin, but if I replace the 10ohm resistor with 330ohms, it is far too slow. Any ideas? I have tried a TIP3C transistor as well to no avail.

Edit: I suppose my question now is I’m losing too much power in the transistor. Would a mosfet help with that? In addition, what’s a good small board that uses 3.3V that also has some sort of usb connection?

Edit 2: Read latest comment, tried MOSFET and fly back diode, now it just clicks and restarts :/

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    The NTE24 is an NPN transistor, so the emitter needs to go to ground and the collector to the load. You could also be causing your lipo to sag too much. I wasn't aware that there was any Arduion Mega specified for 3.3v operation, but even if there is the cell may sag under load to below a 3.3v regulator's input requirement, so it's often better to use a 2.8v or 3.0v regulator for such an application to provide more headroom. And today people would use an NFET rather than a bipolar transistor. – Chris Stratton Sep 20 '17 at 23:54
  • @ChrisStratton the configuration he is using is the common collector one; it is perfectly valid in the analog domain, but I think that the OP should switch to the common emitter version like you suggest; the PWM wave will then power correctly the motor. As for the base resistor, 150-200 ohms is the minimum value the OP should put (otherwise the uC will fry its output). As for the arduino-mega at 3.7V, you are right; it is out of spec. At those voltages better use a 3.3V board (usually arduino micro can come in 3.3V variants, or other ones like the STM32 based ones) – frarugi87 Sep 21 '17 at 12:01
  • @ChrisStratton I switched to common emitter, and I tried putting two 330ohms in parallel to drop resistance to around 165ohms, but the arduino starts resetting again, 330 is about as low as I can get. When I plug both ends of the motor straight into the power source it goes much faster than through the transistor. Should I try Mosfets? I know 3.7V isn’t good for the mega, so I’ve been trying to look for 3.3V arduino boards, but I can’t find one that have a usb B or A Port, which is really helpful. Any suggestions? – Matthew de Soto Sep 21 '17 at 18:17
  • Did you remember the flyback diode? – Ignacio Vazquez-Abrams Sep 21 '17 at 19:12
  • @IgnacioVazquez-Abrams Where would I put that? Wouldn’t that only help with protecting the transistor? That doesn’t seem to be the problem, it seems like something with the transistor dissipating too much power at 330ohms, and drawing too much base current from the pwm pin with less ohms – Matthew de Soto Sep 21 '17 at 19:19

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