Getting pulses to control a separate stepper driver

[Staffscrocs]

Hi, I am building a power feed system for a machine in my home workshop. I have a large stepper motor (7.8A) and its proper commercial driver but to control the functions I need a few basic inputs and a variable trigger pulse to feed to the driver.
I am fairly new to PICs and not sure of the way forward for the pulse thing. I have sorted out enable and direction signals OK.
What would be the best route to try with the picaxe programming? I have an ordinary 18 chip at present and wonder if I need an 18x with PWM and use that feature?
Any suggestions gratefully received!
Regards
Les

 

[Rickharris]

I would suggest reading the interface PDF file in the programme editor help. - search for Stepper motor There are sample programmes that might help you.

 

[Staffscrocs]

Thanks Rick,
I don't need to program the chip as a stepper driver, I am using a big commercial driver unit. What I need are the pulses that trigger the commercial driver unit. The motor runs at 400 pulses per revolution so I need something to generate and vary the frequency of these to control the driver unit.
Les

 

[RMParkhouse]

well im not very experienced in electronics or anything but in school when we want to play with CRO's we just hooked up an astable 555 timer and used either a variable capacitor or change the circuit slightly nd used a variable resistor to control the frequency. you might need to amplify the signal slightly but that might work, but ofcourse im only a novice as far as electronics goes so maybe it wouldnt work for what you want

 

[Staffscrocs]

My initial thoughts were with a 555 and I have tried using one. It works but the variable bit is not so good. I have been told that I should be able to do the job easier and neater with PICs.
I just want the PIC to send pulses like the 555 but allow me to vary the frequency more precisely. I am considering an input switch with, say, 10 different resistance values so the PIC would give 10 different speed signals to the stepper driver. I am playing with PULSOUT at the moment but wonder if PWMOUT would be better?

 

[BeanieBots]

You've not indicated any specification for the pulses. Do you require a variable frequency square wave or would a pulse stream be OK? What sort of frequency do you need?

To get a pulse stream all you need is something like this.

main:
pulsout 1,N
pause D
goto main

where N is the pulse width in 10's of uSecs.
and D is the time delay between pulses in mSecs.
The loop itself will take about 500uS which will need to be taken into account.

Both N and D can be substituted for variables which the rest of your program can change as required.
For input control, consider using a potentiometer and an analog input. This would give you 256 speed steps.

 

[Staffscrocs]

I need just a stream of square wave pulses that can be varied in frequency.
The commercial driver has an opto-isolated input that accepts 5 volt 12mA pulses to trigger a step. The lowest driver setting for steps is 400 pulses per motor revolution. I would like the motor to do a minimum of 10 RPM up to maybe, 200 rpm. So we are talking 66.6 pulses per second to 1333.3 PPS to achieve this.
A potentiometer is an obvious advantage and I would like to go that way. I was initially doing fixed speeds to make it easier to program with my slowly developing skills!

 

[BeanieBots]

The method I described will be close but it could not get up to 1333.3 PPS.
(probably about 990 PPS max. when you include a readadc command)
You might like to consider over-clocking to get the extra frequency. Doubling the clock frequency would give you delays of 500uS steps.

 

[Staffscrocs]

Experimenting this afternoon, I have put in

Main:
pulsout 3,1
pulsout 3,1
goto main
I think this should be the fastest pulse rate I can get and certainly gave the fastest RPM of the motor at about 140 RPM.
I now need to get another PIC as mine (basic 18) cannot do higher frequency on the clock. Looking at a post here by Chris deHut, I will try a 28x and use the pot program he was given.

Thanks for the help thus far!