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David Ashton
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Temperature Meter
David Ashton   2/8/2014 4:13:20 AM
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Page 3 shows how to make a temperature meter with a cheap DMM.  However it only works from +10 to +125 Degrees C.  Not much good in Canadian winters...

The datasheet for the ICL7106 (which is almost universally used in these meters, along with its lower power sister the ICL7136, shows how to make a temperature meter using an NPN transistor and 3 resistors, a cap and 2 presets.  I've never done this but I know someone who did, I think it will do negative temps as well.  

The LM/TMP35 used above gives an output voltage proportional to degrees C, but the LM335 gives an output proportional to degrees K.  Although this is more difficult to work with, it should be possible to use that and make a degrees C (or F) reading thermometer which does negative temperatures.  You can use the ref pins on the ICL71x6 to provide a stable offset to give a zero reading - as in the ICL7106 datasheet app.

David Ashton
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Fluke Mods
David Ashton   2/7/2014 8:08:08 PM
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Hi Caleb, thanks, nice collection, there are some smart guys out there.

I have a Fluke 8050 (page 4) - although about 40 years old now, they are a great bench meter but the displays go black after some years - maybe that's why the guy did the mod?.  I was lucky enough to find a replacement one for mine about 20 years ago and since then it has been good, but I'd look at doing something like this if it went wrong again.  I've also seen a mod that replaced the LCD with 7-segment LED displays (and it is referred to in the article you link to)  - I downloaded that as insurance, as I will this one!   I also have a Fluke 8020A - 3-1/2 digit little brother of the 4-1/2 digit 8050A - and had the same problem with the LCD and was also lucky enough to find a replacement.  But you could do a similar mod there.

Incidentally, you refer on page 4 to a "Fluke 8050A Scope" - I think you meant DMM?

Susan Rambo
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Nice hacks
Susan Rambo   2/7/2014 8:05:44 PM
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Nice hacks to some cheap test tools. Thanks Caleb.

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