Help! DIY 4 amp L297/6203 driver

[cncezee]

The point of the pic is an alternitive clock, the data sheet stats "that if more than L297 is connected then the clocks should be connected to syncronise the circuit", just to the right of the pic is a change over jumper one side grounds pin OSC on the L297 the other wires in the RC oscilliator components 22k and 3n3F. the pin of the pic which is wired to the (top) of v ref pot is a pullup and will have no effect in modulating Vref or anything else
Roger

[irving2008]

The point of the pic is an alternitive clock, the data sheet stats "that if more than L297 is connected then the clocks should be connected to syncronise the circuit", just to the right of the pic is a change over jumper one side grounds pin OSC on the L297 the other wires in the RC oscilliator components 22k and 3n3F. the pin of the pic which is wired to the (top) of v ref pot is a pullup and will have no effect in modulating Vref or anything else
Roger

Roger,

Not sure if you are looking at the same diagram we are, but the PIC very definitely does connect to Vref - the 3.9k resistor and 1k pot are a potential divider to make the max value of Vref = 1v (blue wiring). The PIC clearly has the ability to ground the top of the pot which will drop Vref to about 20% approx (assuming the PIC output is 0.2v) of its set value.

The OSC circuit (red wiring) does indeed have a jumper on it, but thats to enable an external oscillator input for the reasons you suggest, and has no relationship to the PIC or Vref circuit.

[Ross77]

Hi Roger, I think I know what you are refering to as I have seen cuircuits that use a Pic for the clock frequency, but this circuit definetly uses the Pic to change the Vref.

Ok so no luck finding the code for the pic, plently of references to its theoretical use but no specifics. There are plenty using the 555 timer circuits tho.

The closest I can find is the Rotary table drive that kwackers posted. apparently it was designed to drive an L297 setup and provide a holding current using PWM on the Vref pin. The only problem is I cant open the hex and wouldnt know what to look for any way. Maybe I will have to ask him direct for help :whistling:.

Ive also found conformation that this circuit was never built or tested so Im inclined to leave out the Short-circuit protection for the motor wires to keep it simple. may be I could look at it later and just use a known design to get the mill working?

[Ross77]

Progress so far is three options.

1. Basic . as per data sheet but with half step boost and ne555 controling the idle current reduction
2.Ideal. as basic but with PIC controlling the idle current reduction and shunt reg to stop over voltage (not sure if I need to include the mosfet from the original as well?)
3. Complete. as above but with output short-circuit protection. (not sure about that now as it is quite different fron the data sheet! posted earlier)

Any thoughts, omissions or additions?

[irving2008]

There is an error with the Vref circuitry with the 555... Vref should be connected to the slider of the pot...

[Ross77]

Cheers thats the advantage of a fresh pair of eyes I thought I'd fixed most of the errors.

Any thoughts on using the short circuit protection and if i need the mosfet in the shunt regulator?