A4988 module ... pulling inputs


This is probably a recurring topic but ...

I am using this A4988 based stepper driver module:

This module and all other similar modules I could find have Step and Direction floating inputs (not pulled) and Enable is pulled down. This seems to be the worst case scenario concerning Arduino (Nano).

When Arduino is started the digital pins are configures as inputs so the driver will be enabled and Step and Direction will suffer from 'interference' type generated in wiring.

Enable is pulled down (module) by a 100K resistor. To pull it up placing a 4.7K to +5V solves (part of) the problem but still it looks like not very kind to leave inputs of the microcontroller and A4988 to stray signals.

The way this modules are being done seem not a very safe configuration. Am I wrong?

Just in case I modified the modules using 4.5K resistors to pull Step and Direction down and pull Enable up.

Just in case, please be aware that placing the heat dissipater over the driver will very probably sort several surrounding components because some of them are higher than the A4988 itself.

H. Martins

On chip pullups and pulldowns are normally there if its reasonable to not connect that pin in some cases.

There is a tension between providing pullups and pulldowns to prevent undefined states, and avoiding them
to allow micropower operation (typical pullup resistors if conducting consume orders of magnitude more power than a CMOS chip in shutdown mode).

Just one of those things to check and be aware of when reading datasheets..

"to allow micropower operation "

Well, could be, but that function (Speep) is disabled in these modules unless we cut the pcb wires.


OK, OK, I know what you mean. I am using a module 'shield', that's why I don't have access to Sleep.

H. Martins