5i25 controlling PWM servo driver

I'm gradually climbing up a rather steep learning curve as I replace the old Anilam Crusader II controls on my knee mill. My original purchase of a 5i25 along with 7i77 & 7i76 daughter cards is looking rather hasty now that I have a rather better understanding of the differences between analogue, step/direction and PWM drives!

My original plan was to use the 7i77 to control the old analogue drives, then replace them with more modern step/direction drives controlled by the 7i76. However I didn't realise that plan would lose the feedback to LinuxCNC and hence be a retrograde step.

Now - having accidentally blown one of the old drives (no great loss tbh, given the terrible noise it made the Z axis generate!) and following advice from this forum - I realise that replacing the old drives should be quite a bit cheaper if I use H-bridge drivers and control them with PWM. Unfortunately it seems that neither of my current daughter cards (7i77 & 7i76) are able to output this sort of signal, but the 7i85S does seem to fit the bill.

Am I correct in saying this, or is there some way of configuring the existing cards to output PWM so I can get away with using one or both of them instead of investing in the 7i85S? At least this is a relatively cheap card, so if it's the right item I won't be too upset as I'm sure I'll be able to use the existing cards elsewhere.

On the upside the 7i77 seems to be reading the old linear glass scales perfectly and I'm sure there won't be any problems getting it to talk to rotary encoders when the time comes.

Ben

You can configure a 5I25 to output PWM/DIR instead of STEP/DIR on some or all of the 7I76 outputs
but a 7I76 doesn't have a way to read encoders so its fairly awkward

Ah! I was hoping for an answer something like that. I'll see how much space I've got left in the control box - it may be possible to fit both the 7i77 & 7i76 in there at the same time.

Now the obvious question: How do I go about getting PWM out of the 7i76? I didn't see any mention of that in the manual....

Thanks

Ben

I would have to cobble up a 5i25 bitfile that supports the 7I76 and 7I77
but with PWM / DIR on the 7I76 output pins rather than STEP / DIR
I can try and do this after Thanksgiving.

Hi PCW

That would be very kind of you - have a great holiday!

Ben

freeby.mesanet.com/7i77_7i76p.bit

Is a 5i25 bitfile that supports a 7I77 on the primary connector (DB25 on bracket),
and a 7I76 on the secondary connector (26 pin header) that has PWM/DIR outputs
in place of the STEP/DIR outputs.

You will need the mesaflash utility to update the firmware