Re: Pulse Gen

Dan Mauch wrote:

> Could you also provide artwork for a through hole version PCB ?. If you do
> then I would volunteer to have some boards made and low cost kits made
> available to those that wanted one but can't handle surface mount or want to
> search for parts.

> >The problem:
> >
> >It presently takes a fairly powerful computer to generate relatively
> >mediocre step pulse rates (<100 kHz for a 500 MHz Pentium). No one I
> >know complains their step frequencies are too high.
> >
> >The solution:
> >
> >Relieve the PC of the burden of having to generate step pulses
> >directly with external hardware.

I already have 1/2 of this done, which is the quadrature encoder counter, which
can be used to count step pulses. I will, as soon as I get time, design a
frequency generator that will be a companion to this. It will generate step
pulses for 4 axes at rates from 5 MHz down to .596 Hz
The step rates at the upper end are not too usable, as the steps get larger
as a percentage between rates, but anything up to about 1 MHz should be
fine for all purposes. (Even microstepping, that's going faster than almost
any stepper can go.)

The idea here is that the steps are totally un-synchronized with the computer,
but the counter keeps track of position at all times. The computer outputs
velocity information to the rate generator, just like a servo system, and
observes position changing from the counters. If you have encoders on the
motors, you can also break the electrical link between rate generator and
counter, and feed the counter from the encoders, thereby having closed-loop
stepper control. This way, you also get DRO capability when the stepper
drivers are turned off.

The 4-axis encoder counter is all on one Xilinx chip, with an interface to
be controlled by a parallel port in EPP mode. I have this all working,
with PC boards made, etc. What I was proposing to do is design some
different logic using the same chip and PC board, such that it becomes
a 4-axis rate generator.

The current version of this stuff runs to about $135 in parts for the complete
board, so that would get up to about $270 in parts for the counter and rate
generator. Of course, in volume, all of this stuff comes way down in price.
We have already made motherboards that will accomodate up to 8 of these
boards, so you could have more than 4 axes, digital I/O for limit switches and
auxilliary control, and maybe eventually a pendant/control panel interface.

Jon