RadioBanter - View Single Post

November 27th 05, 03:31 PM posted to rec.radio.amateur.homebrew

wrote:
1n914/4148 as silicon temperature sensor. (forward bias)

I used a 1n4007 as a temperature sensor to repair a water bed
heater.

What is the rest of the circuit you used?

A 741 op amp was used as a comparator driving an opto-isolator
triac driver. A triac then controlled the heater. The op amp
compared the voltage across the diode to a fixed voltage provided
by a three terminal regulator and a 10 turn pot. The wiper of
the 10 turn pot was connected to a single turn pot that
then provided the temperature setting. The two pots in series
were needed because the range of adjustment was very small
(the voltage across the diode varies with tempature, but the
change is small over the range we are interested in for
a heater controller.)