Hi there,
First ever post here and hopefully my last as usually I tend to work things out for myself but this has me puzzled!
I shall start off with a short story. I have built and designed a (crude) stepper motor control board for use with a home made (but not made yet) CNC mill using the DRV 8825 driver (3 of) and parallel port etc.
The whole thing was built using toner transfer method (I'm a hobbyist and yes, htssop 28 is frustrating to get right with toner transfer!) But it works nonetheless.
Except for 1 driver, where the mode setting doesn't seem to work and I cannot figure out why.
So, some specs:
35V 10A DC supply
Vref 0.7V
iSense 0.1Ohm (100mOhm)
Now, the other 2 drivers work perfectly fine, not a hitch, but the third one refuses to work with the MODE selection. Now the selection is made by inserting jumpers onto a pair of header pins (im too tight for DIP switches) and when the jumpers are removed, all MODE pins have pull-up resistors and sit at a healthy 5V for 32nd uStep and I have checked with a scope that they are 5V too.
Soon as I insert a jumper, that pin gets pulled low but there is NO effect on the step setting.
I have tried all possible combination of MODE settings but it doesn't change in the slightest.
Am I perhaps missing something?
I've looked into it a little more, turns out that M0 and M1 are working correctly which means I can select 32 or 8/step but M2 doesn't which is why I can't select the full/half 1/4 step rates.
As I say, I've checked also that when the jumper is removed the M2 pin is at 5V and when the jumper is put in place its pulled to 0V.
Broken chip perhaps?
Hi Nigel,
It is always a possibility the device was adversely affected during the soldering process. Are you checking the voltages right at the device pin? If this is where you see the right voltage levels, then best think is to change the device for a fresh one.
Let us know if there is anything else we can help you with. Best regards,
Jose Quinones
Hi Jose, thanks for your reply.
I believe you may have a point. I was checking the device voltages at the pin.
I have since changed the device over for another and it has fixed the problem. I was also having another peculiar problem with another device where the enable pin was directly coupled to ground even though there was no visible connection. I changed that device also and it is now working perfectly.
It is a shame that these devices don't come in a package that is somewhat a little easier to use as they are so small.
TI must be commended though for fitting such a large amount of features and power into such a tiny package.
Thank you.