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[PhilCrompton]

Hello Tom,

I have finally got my homebrew Arduino Mega AstroEQ built but I am now having problems with setting the reference voltages on the 8825 driver boards. They both read 11.37-11.38v and no matter what I do with the pot it doesn't change. Needless to say the stepper motors get very hot and they don't turn either. I have tried connecting them using EQMOD.

I have checked the GND, VDD, VMOT and SLEEP pins on the 8825s and they are reading the correct voltages.

Any ideas?

Kind regards,

Phil

[jmaurin]

Exactly same problem.

[TCWORLD]

A couple of people have seen this before. It usually means either the IC or potentiometer is faulty, or the board is a poorly designed clone. I've seen cheap clones that don't actually wire up the potentiometer correctly which results in almost 12V on the Vref - at which point the IC will be completely fried.

Best case scenario, return them as faulty to the people you bought them from and either get a replacement or find another place to buy them from. If you bought clones from somewhere like eBay, I'd highly recommend you buy from a reputable store like ProtoPIC (UK), CoolComponents (UK), direct from Pololu (US+Int), etc. You are much more likely to get something that works even if it costs a fraction more - plus if they don't work it is far easier to contact the store and get them replaced.

I've only seen 2 faulty boards out of the 250 or so that I have bought from Pololu and ProtoPIC. Both of those were replaced without any hassle.

Also, could you take a close-up of the driver boards for me.

[PhilCrompton]

Hi Tom,

Thanks for the answer. In the meantime I found the following page:

http://www.my-home-fab.de/Documentations/Technical-descriptions/DRV8825-Adjust-Stepper-Current/en

It turns out that some of the boards cannot be set using the ref point but you have to use the centre connection of the pot. Which seems to be the case with the boards that I have.

As far as the pedigree of the driver boards goes I did have them working on a bread board rig at Christmas but I didn't get as far as setting the reference voltage. I have attached some close ups anyway.

Phil

p.s. Just found this one as well which describes the "Made in China" boards and how to set the ref voltage.
http://reprap.org/wiki/A4988_vs_DRV8825_Chinese_Stepper_Driver_Boards

[TCWORLD]

I suppose then whoever cloned the board didn't stick the via on the correct trace. On the official boards it is one trace over (to the middle pin of the pot).

Thanks for the links at any rate, hopefully it should prove useful to others finding the same issue.

[PhilCrompton]

Just a quick update. My Arduino AstroEQ now lives (well both DEC and RA motors turn when holding the buttons in EQMOD)!

I set the reference voltage using the centre tab on the pot to 0.4V. The motors were not turning due to me misunderstanding the connections to the stepper motor. I eventually worked it out and now have them both turning.

In case it is of any help this is what I ended up with. I am using the bipolar NEMA 14 stepper motors as listed on the custom build instructions and the connections seem to go thus:

VMOT
GND
2B (B2)->Blue
2A (B1)->Red
1A (A1)->Black
1B (A2)->Green
FAULT
GND

I have listed all the connections down one side of the DRV8825 because depending on where you look these are labelled differently which is what caused my initial confusion. The pin labels in brackets are from the Pololu diagram. The others are from Tom's schematic.

Phil

[TCWORLD]

Hi Phil,

The discrepancy in labelling is because the DRV8825 and A4988 use two different labelling schemes!

I will add a note in to the next version of the schematic to clear that up.

Kind Regards,
Tom.