Digital resistor substitution?

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?

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Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
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Glenn Ashmore
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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?

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   Robert Monsen
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Robert Monsen

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Check "Digital resistor substitution" on abse
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John Fields

"Robert Monsen" wrote

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.

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Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
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Glenn Ashmore

speed

1.6K

Can't

Good idea. I had completely forgotten about reed switches. That will work perfectly.

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Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
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Glenn Ashmore

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Thanks.  BTW, there's an error on the schematic; E1 needs to go to +V
and E2 and E3 need to go to GND.
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John Fields

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Aaarghhh!!!
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