Temp Sensor

[Buford]

I'm looking for a little ciruit to light one of three LED's in response to temperature, using a small probe.
One LED should light if the temp reaches approximately (somewhat user adjustable) 80 degrees F, a second LED should light at 90F, and a third should light at 100F.
Input on sensors and dedicated chips/subassemblies or ready-made gadgets appreciated!

[bodgy]

Fiddle with a bar led display IC - get the voltage divider right and it should work - assuming your temp sensor is either a voltage or current device.<p>
Colin

[Buford]

That's along the lines of what I was thinking -- wonder if anyone has experience with some of the temp sensing diodes like the ones from National Semi? When I did something somewhat similar seveal years back, I used a couple of comparators and a thermistor. The special diode should be better (more linear), and the bar graph IC should simplify the set-up. Any further input would be appreciated!

[josmith]

An lm334 puts out 10mv/degree f and doesn't require supply voltage requlation. Scale it to you're bar graph and you're done.

[ACE37918]

Check out Nuts & Volts April 2003 page 64 Measure and Display temperatures by Ray Green.

[Dimbulb]

a dual opamp as a comparator and a stable reference voltage is compared to the voltage across a thermistor.