Microstepping code picbasic pro

[HenrikOlsson]

Hi,
Microstepping relies on good, precise current control/regulation, that's the whole point with microstepping. You move the rotor from one full step position to the next by gradually changing the currents in the two coils as opposed to fullstepping where you just reverse the polarity/direction of current.

With a chip like the L6207, it handles the current control/regulation. It'll be your job to tell it how much current at any individual microstep and feed that to the two VRef inputs.

You don't want to implement the current control/regulation in the PIC.

[Galder02]

Ok but the microstepping thing, it can be done with the pic right? And actually use it as the control of the motor, and the chip you mention or the l298 can do the driving. So I could make a board with both things, control and driving, and from parallel port control the motion.

[Demon]

Technically you can do practically anything with PICs and PBP. The limits are your budget, skill, access to parts and patience.

I will build a small light-duty CNC machine using PICs, once I do all the tasks I've already started.

Robert

[richard]

other than as a hobby or an educational process why bother when you could buy this

http://www.ebay.com.au/itm/Single-Ax...-/400738287623?

or this

http://www.ebay.com.au/itm/CNC-Route...-/221654357464?

for such a little amount , you could not homebrew it for less

[HenrikOlsson]

Geez, it seems you still really haven't grasped the concept here.

The L298 doesn't contain any current controller so if you're going to use that you need some way to regulate the current to whatever level your PIC commands. Remember that when you're microstepping you're NOT just setting the coil current to 1.2A or whatever - the current reference for each coil is changing. The L298 is often combined with the L297 and IT has the current controller in it. Oscillator, flip flops, compartors, blanking time etc etc. But since the L297 also has the step indexer built into it it's "locked" to full and half step mode.

The L6207 i mentioned has the H-bridge (like in the L298) but also the current controller part of the L297 (well perhaps not the same circuit but the functionallity).

If you DON'T use a chip with built in current controller you're going to have to implement that part of the chips circuitry with other parts or in code - possible but not easy, certainly not in the code alone.

In the Microchip App note it looks like they are simply and "blindly" throwing PWM dutycycles from a SIN lookup table at the H-bridge without actually regulating or limiting the current. The two sense lines from the H-bridge IS connected to the ADC inputs but the only analog input read in the firmware is AN0 which is the speed reference - as far as I can see. It might work, sort of, but I think it's a very crude way and certainly one that will destroy the motor when the powersupply voltage is higher than the rated motor voltage (which, as you've found out, is needed to get any sort of speed out the motor). Either I'm missing something or that design is seriously flawed.

Then of course, Richard is right, it'll be much easier and cheaper to just buy something - but where's the fun in that right?

/Henrik.