Hi,

I have built a PCB to control 2 stepper motors at the same time. I'm using 2 darlington switches, and serial comm to control the stepper motors. However, if I run both motors together, the first time works perfectly, but whether it works the next few times is quite random.

I noticed that the motors work if the current measured by the power supply is maintained at a certain level(~>1A). But the current keeps dropping after the first time the motors turn.

Any possible ideas what causes the current to keep dropping? Because if I only connect 1 stepper motor to the same PCB, it turns perfectly everytime.

 

What size caps are you using for driving?

 

Also check that you have clamp diodes. They may be built in to your darlingtons if they are designed for motor control.

 

I'm using darlington ULN2064B. It has built in diodes, which I suppose refers to the clamp diodes?

I'm not sure though about the caps used for driving, as I'm not using any caps for the stepper motor at all. Could it be because of this reason that my motors are not working?