Digital resistor substitution?

G

Glenn Ashmore

Guest
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
 
On Thu, 10 Feb 2005 09:14:05 -0500, "Glenn Ashmore" <gashmore@cox.net>
wrote:

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?
Click to expand...
---
Check "Digital resistor substitution" on abse

--
John Fields
 
"Robert Monsen" <rcsurname@comcast.net> wrote
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?
Click to expand...
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
 
"John Fields" wrote ,
"Glenn Ashmore" wrote:

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?

---
Check "Digital resistor substitution" on abse
Click to expand...
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
 
On Thu, 10 Feb 2005 17:19:56 -0500, "Glenn Ashmore" <gashmore@cox.net>
wrote:


Good idea. I had completely forgotten about reed switches. That will work
perfectly.
Click to expand...
---
Thanks. BTW, there's an error on the schematic; E1 needs to go to +V
and E2 and E3 need to go to GND.


--
John Fields
 
Glenn Ashmore wrote:
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?
Click to expand...
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.
 
On Thu, 10 Feb 2005 17:37:57 -0600, John Fields
<jfields@austininstruments.com> wrote:

On Thu, 10 Feb 2005 17:19:56 -0500, "Glenn Ashmore" <gashmore@cox.net
wrote:


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

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

--
John Fields
 
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