[sdiy] Voltage controlled resistor, sort of

[David Ingebretsen]

I'm still in the throes of my Steiner-Parker resurrection. I am looking at
his Trigger generator from the Synthacon schematics. It is a very simple
oscillator using a typical UJT oscillator.

      +       +
      |       |
      |       |
    __|       | 
    |  /      /
    |  \      \
    |->/      /
       \      \
       |      |
       |      | 
       |     _|
       |    |
       |----|
       |    |_
       |      |
       |      |-------------- out to NPN transistor to create an "S-Trig"
output
     __|__    \
     _____    /
       |      \
       |      |
       |      |
      ___    ___
       _      _


I want to replace and/or supplement the pot with a voltage controlled input.


To that end, I decided the charging circuit was really dependent on the
magnitude of current, so I built a voltage controlled current source (VCIS)
from an OpAmp and the simulations work fine, but I was wondering if someone
could point me to a "standard" way to replace a pot like this with a voltage
control? I like the OpAmp solution, but in order to get the thing to work, I
need to run the VCIS off +/-15 VDC with the UJT circuit running on + 12 VDC.
I'd rather not have to re-invent the wheel especially when I'm just
re-learning all this.

I know there are much better ways to generate a series of trigger pulses,
but that defeats the resurrection mode I'm in. I'd really like something
that runs on +/- 12 VDC to keep the power supplies simple.

Thanks

David



David M. Ingebretsen M.S., M.E.
Collision Forensics & Engineering, Inc.
2469 East Fort Union Blvd. STE 114
Salt Lake City, UT 84121
www.CFandE.com

801 733-5458 Office
801 842-5451 Cell

dingebre at CFandE.com
dingebre at 3dphysics.net