RE: [CAD_CAM_EDM_DRO] stepper pulser, and RE: Stepper driver question (slightly O.T.)

HI Richard,

I've currently got code running on two different PICs for the Stepper Driver
project: 16F819 and 18F452.

The 16F (18 pins) can't generate steps as fast as the 18F (40 pins) running
40MHz internally. I generally like more pins/functions to develop with
initially; afterwards the pin count can often be reduced (package size as
well.

The current Stepper Pulser simply uses a SPDT switch (or a pair of PBs) to
start motion in a selected direction and a POT to control the speed of the
stepper. This should be perfect for just moving a single (A, X, Y or Z)
axis. Acceleleration/deceleration and speed is controlled by the PICs code.


No "sensors" involved at this point, although the goal to have the PIC
decelerate to stop and then accelerate to back up to speed on a direction
change. This is currently working! The POT can also be changed while
moving to smoothly accl/decel to the new speed. So this is a start at
handling the failure modes you mention.

For "stock" control, and probably your Heliostat as well, limit switch
inputs would have to be added, and an "automatic" algorithm added to allow
the stepper to be controlled in an automatic fashion, rather then inputs
from a switch or PB.

Sounds like this "limit switch" reversal would also handle the "coil
winding" algorithm as well, however I suspect using a defined distance to
transverse the coil would be better in that instance (a "canned" CNC
approach would serve it just fine).

Contact me off list and we can discuss this more!

Alan KM6VV

> [mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Richard L. Wurdack
>
> There may be logic states that you want to accomodate as well that are
> simple in a PIC but complicated in a BEAM type control - such as power up,
> power down, and various failure modes such as simultaneous true from both
> sensors.
>
> Alan,
>
> I have been considering a similar device using a PIC to the one you're
> working on. (One of my applications is a Solar array tracker.) Please let
> me
> know when you have a design.
>
> Thanks,
>
> D.
> ----- Original Message -----
> > HI Dave, Marv,
> >
> > You're right! The 555 timer circuit posted in the files could ramp a
> > stepper up. Add comparators, and you might have it.
> >
> > But just changing directions may not be enough. Some hysteresis may be
> > required, so that the device does not "hunt". How wide would the "dead
> > band" (area between limits where no motor activity is desired) be? I
> > suppose if a "limit" (photo detector, what type?) was reached, one could
> > simply move 1/2 the distance across the dead band.
> >
> > Contact Dave or I off list if you're interested in a PIC solution. Dave
> and
> > I are currently working on a "stepper pulser" that runs a stepper with
> > proper acceleration/deceleration in either direction when a switch or
> push
> > button is actuated. Your project doesn't sound like a big leap from
> ours.
> >
> > A stepper driver would be required; an LMD18245 stepper driver would
> work,
> > or you could order a single axis Xylotex board. The ELS board (ELS
> list)
> > would be a candidate; it has a driver on board. Also has an LCD
> display,
> > which may or may not be desired.
> >
> > Our stepper pulser board is smaller, and may be used with or without an
> LCD.
> >
> >
> > Alan KM6VV