Arduino Forum

Using Arduino => General Electronics => Topic started by: _6ix on Oct 05, 2012, 08:52 am

Title: 2 Wire temp readers?
Post by: _6ix on Oct 05, 2012, 08:52 am
Okay, I'm being cheap again an want to use the temp probe off a broken electronic thermometer (or a temp controller out of a computer psu) but I cant figure out how to get a reading off them... I was assuming it was a resistance that changed with temperature so hooked it to +3 and A0 & tried to read it but got a fluctuating reading so its not that simple.

Anyone have a link or advice as to how to read the value off these salvaged devices?

Thanks in advance...
Title: Re: 2 Wire temp readers?
Post by: johnwasser on Oct 05, 2012, 03:28 pm
The broken electronic thermometer probably used a thermistor probe.  You need to measure resistance at three known temperatures to calculate the characteristics of your particular thermistor.

To read a variable resistor you can't just hook it between A0 and a power source.  You also need a fixed resistor for A0 to Ground. The variable resistor and fixed resistor act as a voltage divider.  A0 then reads the resulting voltage and some math lets you calculate the unknown resistance.
Title: Re: 2 Wire temp readers?
Post by: MarkT on Oct 05, 2012, 03:29 pm
Did you try measuring the resistance with a multimeter?   Some temperature probes are indeed thermistors, some are thermocouples, some are diodes and some are a whole chip.
Title: Re: 2 Wire temp readers?
Post by: _6ix on Oct 06, 2012, 09:04 am
Thanks guys, No I havent tried measuring resistance with a multimeter yet..

John, do you have a link to how I should wire that up?
Title: Re: 2 Wire temp readers?
Post by: johnwasser on Oct 06, 2012, 02:38 pm

Thanks guys, No I havent tried measuring resistance with a multimeter yet..

John, do you have a link to how I should wire that up?


Try a Google Image search for Arduino thermistor.