| Author |
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Glenn Ashmore
Guest
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 Posted:
Thu Feb 10, 2005 8:14 pm Post subject:
Digital resistor substitution? |
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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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Robert Monsen
Guest
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| Posted:
Thu Feb 10, 2005 11:53 pm Post subject:
Re: Digital resistor substitution? |
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Glenn Ashmore wrote:
| Quote: | 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. |
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John Fields
Guest
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| Posted:
Fri Feb 11, 2005 2:21 am Post subject:
Re: Digital resistor substitution? |
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On Thu, 10 Feb 2005 09:14:05 -0500, "Glenn Ashmore" <gashmore@cox.net>
wrote:
| Quote: | 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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Check "Digital resistor substitution" on abse
--
John Fields
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Glenn Ashmore
Guest
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| Posted:
Fri Feb 11, 2005 3:16 am Post subject:
Re: Digital resistor substitution? |
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"Robert Monsen" <rcsurname@comcast.net> wrote
| Quote: |
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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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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Glenn Ashmore
Guest
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| Posted:
Fri Feb 11, 2005 4:19 am Post subject:
Re: Digital resistor substitution? |
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"John Fields" wrote ,
| Quote: | "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
|
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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John Fields
Guest
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| Posted:
Fri Feb 11, 2005 5:37 am Post subject:
Re: Digital resistor substitution? |
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On Thu, 10 Feb 2005 17:19:56 -0500, "Glenn Ashmore" <gashmore@cox.net>
wrote:
| Quote: | Good idea. I had completely forgotten about reed switches. That will work
perfectly.
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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.
--
John Fields |
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John Fields
Guest
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| Posted:
Fri Feb 11, 2005 5:58 am Post subject:
Re: Digital resistor substitution? |
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On Thu, 10 Feb 2005 17:37:57 -0600, John Fields
<jfields@austininstruments.com> wrote:
| Quote: | 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.
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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...
--
John Fields |
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