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 > > Message was sent through the cbm-hackers mailing list > Message was sent through the cbm-hackers mailing list
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