a4988 Step motor wiring

Hi everyone,

I searched for a while but I couldn’t find a similar issue about mine. This is the first time I am using a4988 and I have already blow one :slight_smile: I try to drive a bi-polar step motor and wired as shown b.pololu-files.com/picture/0J336 … f0619afadf except the micro controller part. Before connecting it, I wanted to simulate it manually. However, when it is powered, step motor starts to rotate regardless of the step input even the step pin is not high or low, it is just floating. (When I connect it to high or low, it stops) I expect to control the rotation by connecting step pin to high and low repetitively. Is it normal? In this situation, I believe given pulses to Step pin by micro controller won’t work. BTW, while it is rotating I can control the direction by connecting Dir pin to high or low.

Thanks in advance


When a pin is floating, the behavior can be unpredictable. It is possible that when you leave your STEP pin floating, there is some interference or noise that is causing it to register steps. When using the driver with a microcontroller, the pin should either be driven high or low at all times, so I would not expect this to be a problem. It sounds like you are concerned that providing a step signal will not work; have you tried it yet? If you want to post some pictures of your connections, I would be glad to look them over and make sure it matches the minimal wiring diagram. Also, you might double check that you have your current limit set to an appropriate value for your stepper motor.