Hello all!

This is a great forum with a lot of experts and experience, so was wondering if you guys could help me on an strange issue. I was using Adafruit Motor Shield v1 with my Arduino Uno. Now I'm removing this shield and use ULN2003 in order to prepare for Arduino Mega that is arriving. That's working fine with stepper motors but my servo (lift) has an strange behaviour: since it is connected directly to rail power and to pin 9 in Arduino, it's moving without any reason, erroneously, randomically. It normally happens when steppers are not working but engaged. I suspect that it's some kind of noise or other interference that was not happening when using Adafruit Shield.

Have you faced some similar situation? I put some decoupling capacitors (470uF) in parallel in power rail but with no effect: the problem persists.

Any input would be helpful.

PS: I'm using MicroServo 9G SG90 and the popular 28BYJ48 5V stepper and they are all powered with an external stable 5v source.

Thanks!