Help! DIY 4 amp L297/6203 driver

[irving2008]

Hi All

Im looking to build a new stepper driver for my mill project. The original board used an L297 driver and 2x L6203 H bridge output stage. I'm hoping to build something similar and have found a few circuits on the net.

I have also found some nice additions to the basic circuit like overload protection for the output chips (good idea since I fried them on the last board ) and varable voltage for VREF to increase Half step torque.

The circuit i have used i heavilly based on one I got from an old thread on cnczone but I'm unsure what the Pic chip dose (i asume it detects the clock pulse and varies the VREF accordingly)

So Question 1. can anyone help with a replacement circuit for the PIC chip as I dont want to use PIC chips for this project.?

And Question 2. Can some check over my version to make sure it works or suggest an alternative?

Thanks in advance

At a guess i would surmise the PIC is detecting the clock to the L297 and after some timeout after the last clock pulse is pulling Vref down to reduce the current in the motor. A 555 set up as a monostable with say a 5sec delay and triggered from the clock line might do the trick...

[edit] must learn to type faster![/edit]

[Ross77]

Thanks for the replies

Tribbles
Im not using the optos as i plan to make modular set up with a master board for the optos. Thank for spotting the mistakes, thought it was a funny looking diode :whistling:

The +5 is supplied from the input connector, Bottom left.

Irving

So is the Pic just earthing the 5v supply to the VREF making it 0v which means there is no holding current? I presume it would then revert back when a pulse is detected on the clock line?

[irving2008]

Thanks for the replies...
Irving

So is the Pic just earthing the 5v supply to the VREF making it 0v which means there is no holding current? I presume it would then revert back when a pulse is detected on the clock line?

Well if that was the case it would be pointless IMHO. I had a quick scan round and can't find the original design writeup for this circuit. I am wondering if the PIC modulates the VREF rather than just shutting it off...

[tribbles]

Well if that was the case it would be pointless IMHO. I had a quick scan round and can't find the original design writeup for this circuit. I am wondering if the PIC modulates the VREF rather than just shutting it off...

It could do that - it would reduce the holding torque for the motors as a result. It would then provide the "full" VREF when it's being clocked. It might be a very short pulse...

[Ross77]

Modulating the vref would make sense as no holding current isnt much use. Is that why a Pic is used rather than a 555?

I did find another cuircuit that uses logic gates to trigger 2 separates trim pots but the control signal came from an external source or the software. would it be possible to use a 555 chip to trigger this circuit?


This would make more sense and be easier to setup