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Digital resistor substitution?

G

Glenn Ashmore

Jan 1, 1970
0
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
 
R

Robert Monsen

Jan 1, 1970
0
Glenn said:
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?

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.
 
J

John Fields

Jan 1, 1970
0
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?
 
G

Glenn Ashmore

Jan 1, 1970
0
Robert Monsen said:
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?

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
 
J

John Fields

Jan 1, 1970
0
---
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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