Relay affects thermistor
I have a question about making my simple thermistor circuit more percise.
Long story short: I am using a BS2, and a cheap radio-shack thermistor to build a simple cooling thermostat (fridge controller). I am using RCTIME to measure the capacitor discharge time through the thermistor as described in the BS2 manual. I'm using an LM317 3-terminal voltage regulator to provide 5 vdc to the stamp, and to the thermistor, and to a relay which controls the fridge compressor. Vin is provided by a 12v(ish) AC wall-wort adapter.
I've noticed that when voltage is flowing through the relay in order to close the relay ciruit, this has a somewhat significant affect on the RCTIME measurement of the thermistor. The affect is 3-4 degrees F.
Any ideas on how I can reduce the affect of the relay on the thermistor? Would it make sense to use two LM317s, one for the more-sensitive thermistor circuit, and another for everything else?
I'll draw a quick schematic if needed.
Thanks!
CP
Long story short: I am using a BS2, and a cheap radio-shack thermistor to build a simple cooling thermostat (fridge controller). I am using RCTIME to measure the capacitor discharge time through the thermistor as described in the BS2 manual. I'm using an LM317 3-terminal voltage regulator to provide 5 vdc to the stamp, and to the thermistor, and to a relay which controls the fridge compressor. Vin is provided by a 12v(ish) AC wall-wort adapter.
I've noticed that when voltage is flowing through the relay in order to close the relay ciruit, this has a somewhat significant affect on the RCTIME measurement of the thermistor. The affect is 3-4 degrees F.
Any ideas on how I can reduce the affect of the relay on the thermistor? Would it make sense to use two LM317s, one for the more-sensitive thermistor circuit, and another for everything else?
I'll draw a quick schematic if needed.
Thanks!
CP
Comments
Go ahead and post a schematic, just in case something might be missed in the text description.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
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Chris Savage
Parallax Tech Support
csavage@parallax.com
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Think outside the BOX!