Re: [ATM] USB stepper controller

[Dominic-Luc Webb <dlwebb@canit.se>]

I have already gotten word from Andy on his needs and will not comment
further on that. I would like to point tomy experience on this issue,
and yeah, once again I am probably going against commonly prefered
practice.

First, I have encountered a few problems in the past with commercial
controllers, but probably like a lot of others in here, did not spend
much effort documenting my disappointments in detail to share with
others. On such posts in the future, it would be nice to have something
along the line of a consumer report where problems in such devices get
archived. Problems I have encountered include jumping one or more steps
on power up or down, stalling with small changes in load and sensitivity
to shared power source for IC and motors as by using a voltage divider.
I could probably think of a lot of other things I did not like. Some of
these bugs did not come from cheap build-it-yourself kits, but rather,
from very expensive "top-of-the-line" sources.

My solution was to build my own and for a lot of applications, especially
those not related to track & sweep motion control where switching
between microstepping and full stepping occur, I have found great
reliability in a very simple circuit utilizing only 3 ICs: a 555 timer
connected to a 4017 Johnson counter whose output goes to a 4 diode array.
Speed is tuned with a potentiometer and circuit could easily be
computerized. There is probably some simple trick to make this
circuit even do half and microstepping, but for many applications, such
circuits work gret as is. Building my own stepper circuit was the best
advice I ever got, so I now encourage others to do the same.

Another direction for those who like to tinker: I have built some parallel
drives that use the parallel port output to drive the base of transistors
or opto-switches that were used as switches/relays for external power
supplies that drove rather powerful motors. This way the power draw from
the port was negligible. In this case, one or more motor heads can be
activated at any moment, so half-stepping is quite straightforward.

Dominic-Luc Webb

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