Re: Plasma voltage servo : Mariss?

Todd,

DUH! A Homer Simpson moment here. That is the problem with untested
circuits. Here's the problem and here's what you have to do:

The top and 2nd down comparators form a window detector. The outputs
are connected as a "wired OR" gate. The problem with that is the
output is true (logic 1) in the window. That is the opposite of what
is needed since a logic "0" kills the step oscillator (outside the
window).

Here is what you need to do to make it work.

Disconnect the bottom comparator output from the other two comparator
outputs. These two outputs need to be inverted. Keep the 1K pullup
attached to those outputs.

Place a new 1K resistor from the bottom comparator to +5VDC. Take the
base of a general purpose NPN transistor (PN2222A or like) to the
outputs of the top and 2nd comparator. Take its collector to the
bottom comparator (OSCILLATOR) output. Take the emmiter to ground.
This will form an inverter and the oscillator will run outside the
deadband, not inside as now.

I will pull, correct and repost the circuit. Again, sorry and DUH!

Mariss

--- In CAD_CAM_EDM_DRO@y..., "morgtod" <todmorg@h...> wrote:
> Hi Mariss-
> Further up the thread I mentioned that I built the circuit, but
it
> only steps inside the deadband and we need it to step outside the
> deadband towards the deadband. I believe we are looking at 115-130
> volt D.C. and from what I've read it looks like 1/2 volt is a
pretty
> standard dead band. Due to the variances in every system ( plasma
> brand and steps per inch of movement ) I think it makes sense to
> build the board with sockets for easy component changes or maybe
> variable pots.
> Thanks!
> Todd
>
> --- In CAD_CAM_EDM_DRO@y..., "mariss92705" <mariss92705@y...> wrote:
> > Hi,
> >
> > OK, sorry about that. I haven't been following this thread until
I
> > saw my name pop up.
> >
> > I dashed off this circuit at someone's request some time ago. It
> was
> > designed according to what was asked at the time as far as
deadband
> > and thresholds go.
> >