Digital Thermometer construction

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Fetti

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Hi,
i´ve built up a thermometer from the attached circuit, which is the base of a commercially available thermometer, so it should work. In my case, after switching on, a very brief (and always different) value appears and the display switches to 1 on the first display and the decimal point on the third with the other two displays left blank. Does anybody have an idea, what might be the prob?
Thanx# Fetti

 

Did you used the right displays. Yhere care common anode and common cathode displays. Here you need common anode. But in that case it probably would show nothing.
Biggest change is you made some fault or there is a bad solderjoint. But with only this schematic my crystal ball stays dark ;-)

Have you checked the datasheet ? There are more versions. The 7107 has a different pin out as the 7107R. This is a very much and very long used IC . Fluke made a multimeter with the 7106 LCD version of this IC. (Fluke 8020 ).

Edit: I'm sure it can not be the code because there is nothing to program. The 7107 is a Voltmeter IC.
 


Thanx for help. The displays have common anode, but don´t seem to be the problem. I have two chips of that sort: one is labeled ICL7107CPLZ, the other one TC7107ACPL, but there´s no difference in the result. I think, I can exclude any bad soldering after measurement (by the way, a picture of the card wouldn´t help because of confuse cabeling), so do you think ther might be a problem with the othrt parts of the circuit, or the kind of response gives a hint to a certain circuit like intergrator or oscillator?
 

You make somewhere mistake on PCB or you have bad soldering on some points.

For now I see only that you dont have -5V supply on pin 26 (between D2, C1 and Pin26). Pin 26 must receive good -5V supply. Check that polarity of C1 is just as on circuit. Probably you switch cap sides (+ goes to Gnd and - to pin 26).




About IC difference, only difference exist between ICL7107 and ICL7106. ICL7107 is for 7-seg LED display and ICL7106 is for LCD display.


Best regards,
Peter
 

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