Same repeating problem with all the A4988 boards recieved

Support Motor controllers/drivers and motors
1

Support Group,

All of the A4988 driver boards are giving me the same results.
They are calibrated by the second method, set to 0.65 VDC. The motor is disconnected during the calibration and motor power is off. All inputs pins are taken to logic low. Calibration is set.

Reconnect of motor power and motor phases. Both power sources are turned on the stepper motor proceeds to run without any pulse step input from the SPST pushbutton, low to high transition. When the button is pressed the stepper motor stops running. Note: the SPST is by default normally opened and this was verified via meter.

All inputs have been re-verified several times. All outputs have been re-verified several times. Calibration has been done several times. Reconnecting at different locations on the breadboard has been done several times. Different soldered boards have been placed into the existing breadboard wiring with the same results.

Now tomorrow is my students last day of class, which is also their final exam day and their projects are due. Their projects include the A4988 board. I have solder several of the boards and tested them and still get the same results.

When someone in the group read this please get back with me via my email address also first thing in the morning.

Thank you.

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2

Hello.

I am sorry you are getting unexpected behavior from your stepper motor drivers. Since they are controlling your stepper motors, it sounds like everything is working. I suspect that whatever is connected to your STEP pin is sometimes leaving it floating or creating an oscillating signal. What is the other side of the pushbutton connected to? Do you have a pull-down on the STEP pin to ensure it is not floating when the pushbutton is open? If you do not, can you add one to see if that solves the problem?

Also, do you have access to an oscilloscope? It would be useful if you could remove the driver from your setup and see the signal on your STEP pin if adding the pull-down does not change anything.

-Jon

3

In my many years as an instructor, I have found it important to stay at least one full week ahead of the students!