# Digital resistor substitution?

Discussion in 'Electronic Basics' started by Glenn Ashmore, Feb 10, 2005.

1. ### Glenn AshmoreGuest

Working on a circuit to control a refrigeration compressor speed. The speed
is set by a resistor in the thermostat circuit that can range from 0 to 1.6K
in a logarythmic progression. I have no documentation on exactly how the
compressor's controller works but it looks like a basic RC network. Can't
find a digital pot that would work so I need to find a way to switch 6
different resistors into the circuit from the output pins of a PUC uC
without effecting the circuit in any other way.

Any suggestions?

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com

2. ### Robert MonsenGuest

How about an analog switch, like a 4066? It clearly depends on the
current, but if it's just for timing, there isn't much current.

Also, what's the problem with digital pots?

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.

4. ### Glenn AshmoreGuest

Just looked at the 4066. It looks like both it and a digital pot have to
much on resistance. I need to go from close to zero to 1520 ohms in
discrete logarythmic steps of 120, 270, 450, 690 and 1K.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com

5. ### Glenn AshmoreGuest

"John Fields" wrote ,
Good idea. I had completely forgotten about reed switches. That will work
perfectly.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com

7. ### John FieldsGuest

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Aaarghhh!!!
__ __ __
E1 should be E1 and should go to GND with E2 as shown, and E3 should
be E3 and go to +V, as shown, so the error is in the logical notation,
not the connections...

What next? sighhh...