HElp!LED thermometer using LM324

[marianne]

**broken link removed**

I tried constructing this in a breadboard. All the 7 LEDs light up in normal temperature level. I tried adjusting the potentiometer but still, all of them light up. What is the problem?What value of thermistor should i use?I'm currently using 15k thermistor.

Please help me=)http://imgfreehost.com/out.php?i26540_22022009001.jpg

 

[ccurtis]

Some of the values in your picture are unreadable, but from what I can gather, the reference voltage resulting from series diodes D1 and D2 may be too low for the input voltage range to the LM324's from the thermistor circuit. What is the B+ voltage powering the LM324's and what is the resistance value of the potentiometer? Is that a 9V battery on the left?

 

[user_88]

Check to see that D3, a zener diode is installed correctly.
Negative band should go to positive terminal of battery.
If that is not the problem, then measure voltage at each terminal of VR1 ... the variable resistor.... Observe whether the adjustable leg varies as you change the resistance.
.... Wondering if the zener diode is in fact turning on .... spec sheet says it should conduct about 35 ma at 7.5 volts.