[sdiy] Voltage controlled resistor, sort of

[nicolas]

Can you clarify why you need to run the opamp off +/-15V.  Does the circuit really require compliance right up to V+ ?  Maybe have a look at some of the modern low power opamps with rail-to-rail output that are designed for battery powered gear and then you could run it on a 0V/+12V supply and get compliance to within less than a volt below V+.  Would that work?

Nicolas

--- On Tue, 4/5/10, David Ingebretsen <dingebre at 3dphysics.net> wrote:

> From: David Ingebretsen <dingebre at 3dphysics.net>
> Subject: [sdiy] Voltage controlled resistor, sort of
> To: "'synth diy'" <synth-diy at dropmix.xs4all.nl>
> Received: Tuesday, 4 May, 2010, 6:21 AM
> 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
> 
> 
> 
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