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Old 2nd May 2020, 8:12 pm   #1
Chris55000
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Default Home Built Practical Electronics DVM, 1979, or similar?

Hi!

Has anybody else, besides me, had a go at making the "Auto Ranging Digital Multimeter" published by two Doctors in the April & May 1979 issues of P.E., or another project DVM?

All I managed to get was a very good version of "Ernie!" out of mine!

Chris Williams
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Old 2nd May 2020, 9:54 pm   #2
Oldcodger
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Default Re: Home Built Practical Electronics DVM, 1979, or similar?

Never tried making one, but spent a lot of time in lodgings working out circuits for one from Mags using either 7106 or 7107 with circuits from mags showing how to get auto ranging from the display.
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Old 3rd May 2020, 2:01 am   #3
retailer
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Default Re: Home Built Practical Electronics DVM, 1979, or similar?

I made one, and had good success, pulling the ICL 7106 dvm chip from an evaluation board was probably the most challenging part, the pin holes were through plated making a difficult job even harder, it survived the extraction only suffering bent pins. The case was home made clam shell style in aluminium, red cellophane sandwiched between two thin pieces of perspex formed the filter for the red led display, lettraset on the front panel looked quite professional.
It did work quite well I used it a bench DMM for a few years, - the only draw back was lack of portability. At the time I was making PA amps at home as an unofficial subcontractor for a local music hire business. ie I was paid in cash, it was my goto meter and saw me through many builds and repairs. There were times when it refused to range down and I had to use the range push switch. I had a bit of trouble sourcing the voltage reference and for a time I used a to92 style 5v regulator in it's place.
After getting my first LCD dvm it sat unused along side my home made scope for many many years and I eventually stripped it down to salvage some of the hardware for other projects, I still have the main function switch which I fabricated by adding extra wafers and I also have the relay range switch board populated with reed relays.
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Old 3rd May 2020, 9:03 am   #4
TonyDuell
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Default Re: Home Built Practical Electronics DVM, 1979, or similar?

I've never bullt any of the magazine DMM projects but I bought a second-hand Tandy/Radio Shack/Micronta autoranging DMM. It didn't seem that interesting and I was going to pass it by until I looked at the instruction leaflet with it. The last page was the circuit diagram. It uses a 7106 as the ADC/display driver and a lot of 4000 series CMOS logic ICs for the autoranging. One day I'll work out just how it does it.
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Old 4th May 2020, 12:45 am   #5
Chris55000
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Default Re: Home Built Practical Electronics DVM, 1979, or similar?

Hi!

Can you post the circuit of your Radio Shack '7106 based Autoranging DMM please Tony? What model was it?

Chris Williams
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Old 4th May 2020, 2:02 pm   #6
TonyDuell
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Default Re: Home Built Practical Electronics DVM, 1979, or similar?

It's Catalog Number 22-196A and is simply called 'Micronta LCD Auto Range Digital Multimeter'. I've scanned the schematic from the instruction booklet and attached it.
Attached Files
File Type: pdf Micronta_Autorange_DMM_22-196A_Schematic.pdf (477.0 KB, 134 views)
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Old 9th May 2020, 10:41 am   #7
Chris55000
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Default Re: Home Built Practical Electronics DVM, 1979, or similar?

Hi!

Thank you for that Tony!

Do you have any objections to me making reference to it and using it as a basis for a new 7107 based LED bench design for my forthcoming Test Equipment Theory and repair book?

An acknowledgement citing you as the source of the original documents will be included in the book!

Chris Williams
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Old 9th May 2020, 5:25 pm   #8
TonyDuell
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Default Re: Home Built Practical Electronics DVM, 1979, or similar?

I have no claim on that diagram at all. So feel free to use it, but do make sure you're not breaking any copyright laws (Tandy/Radio Shack could object in principle I guess)
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