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Lockdown Projects

 

Good day everyone,

Just thought I would share something I started during the lockdown, nothing new or revolutionary but it has kept me entertained :)
My Fluke 77 has served me well since 1984 but is showing sings of age so I said to myself, why not build a bench DMM?

This is a simple DMM, old technology and uses 7 segment display. The heart of the DMM is MAX1496 ADC chip, an arduino controls the functions and range. It is still pretty much a work in progress, attached is a photo of it.


With pubs now open probably this DMM will wait for a while :)

Cheers, Elia, M0ZHN
 

Hi Elia,

That is just too cool. I had to scratch build a V-O-M when I was a teenager (or live without one). I made mine in a cigar box with an old mil surplus meter. The shunt and series resistors all plugged into old tube sockets - I didn't have a range/mode switch. Projects like yours get us intimately familiar with how those measurements are made:)

My XYL and I are both fully vaccinated and now they have removed the ball and chains in our locale. I hope that everybody will get back to real life soon.

73,

Bill KU8H

bark less - wag more

On 5/21/21 6:56 AM, M0ZHN via groups.io wrote:
Good day everyone,

Just thought I would share something I started during the lockdown, nothing new or revolutionary but it has kept me entertained :)
My Fluke 77 has served me well since 1984 but is showing sings of age so I said to myself, why not build a bench DMM?

This is a simple DMM, old technology and uses 7 segment display. The heart of the DMM is MAX1496 ADC chip, an arduino controls the functions and range. It is still pretty much a work in progress, attached is a photo of it.


With pubs now open probably this DMM will wait for a while :)

Cheers, Elia, M0ZHN
 

Hi Elia.? Love the project!? Reminds me of being at university when we had to buy a specified multimeter kit (analogue).? We were provided (if my memory serves correctly) with the circuit, required ranges and the meter characteristics.? All the component values had to be calculated, then components of those values were provided and then we had to assemble the kit.? I remember my soldering was not to standard :(? Final test was to calibrate it.? I still have the pieces somewhere - the case was a very brittle plastic, maybe bakelite.? Even tightening up the case screws could crack it and the case certainly did not survive the accidental drop test, though it still worked electrically.

Incidentally I have a Fluke 77 issued to me when I started my job in 1986.? Various segments in the display became faint over time so a few years ago I took it apart and found that there is a sort of conductive rubber connecting the display to the PCB.? Carefully dismantling, cleaning everything up with IPA and reassembling restored most segments, second attempt fixed the lot - could be worth trying on your one if it has a similar issue.

73

Dave M0WID
 

Very nice.

Makes me think of a series in QST back in 1976 I think, that may have been called “Learning to Work with Integrated Circuits” or similar.? The heart of the thing produced a frequency counter, but other devices converted it to a DVM and other functions.? I didn’t get beyond the counter, but it was nice.

It was popular enough that they reprinted the series as a stand-alone booklet.

73-

Nick, WA5BDU


On Fri, May 21, 2021 at 5:56 AM M0ZHN via <eliamady=[email protected]> wrote:
Good day everyone,

Just thought I would share something I started during the lockdown, nothing new or revolutionary but it has kept me entertained :)
My Fluke 77 has served me well since 1984 but is showing sings of age so I said to myself, why not build a bench DMM?

This is a simple DMM, old technology and uses 7 segment display. The heart of the DMM is MAX1496 ADC chip, an arduino controls the functions and range. It is still pretty much a work in progress, attached is a photo of it.


With pubs now open probably this DMM will wait for a while :)

Cheers, Elia, M0ZHN

 

开云体育

Very cool project!

Yeah, Nick, I remember that series and have a copy somewhere in my stack of stuff. Also that same year QST had another 8-part series by Doug Demaw called “Learning to Work with Semiconductors”. I had gotten my novice ticket the year before and that series really hit the mark for me. IIRC you ended up with a QRP transmitter at the end of the series.

To bad QST no longer supports beginner projects such as these.

Don, K5DW




On May 23, 2021, at 7:43 PM, Nick Kennedy <kennnick@...> wrote:

?
Very nice.

Makes me think of a series in QST back in 1976 I think, that may have been called “Learning to Work with Integrated Circuits” or similar.? The heart of the thing produced a frequency counter, but other devices converted it to a DVM and other functions.? I didn’t get beyond the counter, but it was nice.

It was popular enough that they reprinted the series as a stand-alone booklet.

73-

Nick, WA5BDU


On Fri, May 21, 2021 at 5:56 AM M0ZHN via <eliamady=[email protected]> wrote:
Good day everyone,

Just thought I would share something I started during the lockdown, nothing new or revolutionary but it has kept me entertained :)
My Fluke 77 has served me well since 1984 but is showing sings of age so I said to myself, why not build a bench DMM?

This is a simple DMM, old technology and uses 7 segment display. The heart of the DMM is MAX1496 ADC chip, an arduino controls the functions and range. It is still pretty much a work in progress, attached is a photo of it.
<IMG_20210520_221055499.jpg>


With pubs now open probably this DMM will wait for a while :)

Cheers, Elia, M0ZHN

 

Thanks everyone for the encouraging comments, I am thoroughly enjoying building something so seemingly simple but quite complicated when you get down to the details of it.

I had a look at the QST articles, yes very interesting project indeed. My DMM is not that versatile but I may in the future add some of the functionalities, will see. For now the voltmeter function is fully working, calibration not a huge issue, I have carefully selected the divider resistor values so that is ok. I am finding the protection part a bit interesting and challenging, it is something I never gave much thought before but looking at information from different sources it seems that the protection is the more difficult and clever bit, especially for the ammeter and ohm meter functionality.?

I haven't tested it with anything higher than 24VDC yet, next is to build the ac rectifier for ac voltage measurements. Eventually will replace it with a true rms module but a simple rectifier for initial testing will do I guess.

Elia, M0ZHN

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