CNC Rotary table/lathe head indexing

[Ross77]

Brilliant idea I will definetly bulid this, after the other 10 or so projects. Hope you dont mind but a have a question not related to this Thread.

Im looking to build a stepper driver using an L297 and 2x 6203 and I want to use a PIC to control the holding torque. (by varying Vref) I noticed in the last post that your controller was designed to do this. Would you be able to shed any light on the code to do this and how it was integrated in to the circuit?

Many thanks and sorry again to hijack your thread.

[Kwackers]

Hi Ross,
It's pretty trivial. VRef is normally provided via a voltage divider, basically you simply provide your VRef fed via two voltage dividers, one fed from +5v like normal the other fed via the enable line. Unless you isolate the two dividers there's a degree of 'interdependence' on their adjustment so you need to tweak both to get the current correct. (I think I also fed the enable via a diode to prevent it pulling VRef low when the enable line dropped.)
In software terms it's simply a line that's pulled high whenever the motor is running.

Another way that I experimented with and worked well, was to feed one of the PWM's via an RC chain (series resistor feeding a parallel cap, feeding another resistor feeding another cap). Set the frequency high(ish) and change the PWM to alter the voltage (and thus the current). The VRef input seemed quite high impedance so there was no need to buffer this. A 50% pulse width ratio would result in half voltage available. Again in software when idling all that I did was quarter the PWM ratio to drop holding current to 25% of max when the motor wasn't running.
The only reason this didn't make it into the final device was that it worked out cheaper and less messing to buy ready made drivers, which meant that the setup options for setting the stepper current made no sense.

Hope this helps,
Steve.

Brilliant idea I will definetly bulid this, after the other 10 or so projects. Hope you dont mind but a have a question not related to this Thread.

Im looking to build a stepper driver using an L297 and 2x 6203 and I want to use a PIC to control the holding torque. (by varying Vref) I noticed in the last post that your controller was designed to do this. Would you be able to shed any light on the code to do this and how it was integrated in to the circuit?

Many thanks and sorry again to hijack your thread.

[Ross77]

Thanks Steve, thats great. Unfortunatly I've never used Pic's before and therefore I'm a complete novice. Irving and Tribbles have offered to help with the code but just wondered that as you have allready done it we wouldnt have to reinvent the wheel

Im looking at a slightly different set up where the pic is soley used for varing the vref based on the incoming step signal from Mach. If you can help any further maybe you could take a look at me my thread "Help with DIY L297 + 6203" (or some thing like that:heehee:) to save clogging up this one.

Thanks again