Digital resistor substitution?

Feb 10, 2005 6 Replies
G

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 Shameless Commercial Division: http://www.spade-anchor-us.com
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R

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.
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J

Check "Digital resistor substitution" on abse
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G

"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.

Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com
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G

speed

1.6K

Can't

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 Shameless Commercial Division: http://www.spade-anchor-us.com
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J

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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J

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...
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