From: john/lori (lgnjh_at_earthlink.net)
Date: 2007-04-09 11:11:29
Scott McDonnell wrote:
> Anyway, as I get some time this week, I will try to get something
> nailed down as far as what is needed. Right now, I am picturing
> a NPN resistor with the control port 5V on the collector, control
> port ground on the emitter, and a very large value resistor across
> the collector and emitter (the transistor in parallel.) The emitter
> is connected to the POT line. Since the transistor and the resistor
> are in parallel, I can control the total resistance with the transistor.
I think there's something wrong with that description (sounds like
you've got the emitter going to both ground and the POT line for one)
How about a constant current source feeding the POT line with a voltage
controlled current sink (a common emitter circuit) shunting the POT line?
something like:
\
+-----+---- +V \
| | |
| R2 |
V | |
Q1 \| | |
pnp |---+ |
/| | |current source
| V |
| |/ Q2 |
+---| pnp |
| |\ |
R1 | |
_|_ | /
gnd | /
|
+------POT
|
|/ Q3
IN --R3--| npn
|\
V
|
R4
_|_
gnd
> Scott McDonnell
>
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>
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