Re: [CAD_CAM_EDM_DRO] PWM signal to step/direction signals

On Tue, 8 Oct 2002, Howard Bailey wrote:

> Anybody know of a circuit or IC that is capable of taking a PWM signal as
> used for RC angular servos and outputs step and direction signals with
> output adjustable for scaling? Basically, I would have a PWM signal for an
> angular servo and would like to use it to run a stepper through a gear
> reducer to increase resolution and torque. I couldn't find much on the web
> on this so any information would be greatly appreciated.

Eyup... that would be a PIC microcontroller running some custom microcode.

The devil's in the details.

How fast would the stepper have to run?

If all you want is a low-current, TTL-level step and direction signal
based on the PWM duty cycle of a servo controller output, it's a
straight-forward implementation. Then, you'd take this output, and run it
into your preferred stepper motor driver (Gecko, et. al.).

Developing the software to run on an $8 microcontroller to do this is
about 40 man-hours worth of work. It's not dissimilar to some
motion-control projects I've spun in the past.

A normal RC servo driver (bar some ringers) runs at a base frequency
between 50Hz and 400Hz with a typical pulse width of 0.6 mS to about 2.5
mS.

This pulse width is proportional to some angular rotation between 0 and 90
degrees (or thereabouts).

What is the ultimate precision you require for your application?

1 degree is relatively simple to implement. 0.018 degrees would be about
the best a 20 MHz microcontroller could generate.

Does that meet your requirements?

Kind Regards,

David Kott


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