Slightly OT but PIC based servo driver with step/direction input..

--Have you been to parallax.com? Seems to me that's how the BOEBot works...

Can you just use an external interrupt for each step input and a port line for each direction input? Then your ISR would just increment/decrement a 32-bit (or whatever) counter. If you don't have sufficient hold time on the direction input to allow the ISR to capture the direction input reliably, you can just add a D FF to the input. If you use a dual-D for each input you could tie the D inputs high on one FF, tie the other D input to the direction input, connect both clocks to the step input. The outputs for each axis could be OR'd and the microcontroller would only need to have one /INT input- it would come around and find out which input (s) stepped and reset the step FF.

Best regards, Spehro Pefhany

steamer wrote in news:ejcMc.3863$54.54967 @typhoon.sonic.net:

Thanks for the link, however I'm working with industrial servos - DC brushed motors, not RC type servo's. Couldn't see anything on step/direction control either?

i know you want pic... but look at an IsoPod.

you should be able to read 3 s/d pairs, and 3 quad pairs as feedback.

While I realize you're working on your own implementation, I thought I'd mention that this is available as a low-cost commercial product. Gecko Drive makes a brushed DC servo driver that takes step/direction input. It uses a quad encoder for feedback. Their Web site is here:

I doubt they'd offer you the programming they use, but the product and specifications show what can be done with the basic concept you have.

-- Gord>

I can also recommend the copley control amplifiers (although more expensive)

Increase/Decrease the desired position for the (underlying) position PID loop on the step input. Would be interested in a CAN(Open) version of this driver.

Kind regards

Sjur J. Vestli

Copley is really the best money can buy. About 4x the price of a gecko. I have never heard anything bad about the Gecko units.