Shop Tips - Bread Board Voltmeter

5 Nov 2015

There are many times, when I am working on an experiment or project using my bread board, that I want to monitor the voltage at different points in the circuit. This usually involves setting up a couple DVMs and running test clips into the proper positions on the board. This can be messy and inconvenient. I got the inspiration for this shop tip when I saw these small 2.5 volt to 30 volt LED meters on a China Dollar Store site for $2.75 each, including shipping to the shop.

I bought two of the little meters and added some bread board pins onto the wires.

The next step was to calibrate them against my Fluke which is perhaps the most accurate meter in my shop. I calibrated them around 15 volts as I am sure they are not completely linear and this at least centers their range. Surprisingly they stayed within 0.1 volts of the Fluke throughout the range. Since the meters were very light I wanted to mount them to a more substantial base. I cut some small pieces of wood and mounted the boards and also a tilt prop to the back of the boards.

It is important to note that these meters consume about 20 mA at all voltages above 5 volts. This could be a factor and affect our experiment if we are not careful. I have labeled the meters with this information so that I am careful to only use them in positions where their current draw will not affect my circuit or the outcome of my experiment. If I need a voltage reading where minimal loading is required I will have to go back to the old method and hook up one of the DVMs.

For the sake of illustration I have bread boarded an LM7805 and used the two new bread board meters to monitor the input and output voltage of the regulator.

John

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Problemchild over 10 years ago

Good one John, I've started doing the same thing after I saw someone doing a demo at a meeting doing the same thing.
He was using it to remind himself that it was 5V not 3.3V to prevent him blowing the 3.3V chips .

Personally I think it will be even better in situations where you are showing an experiment with several voltages and currents and then you can demonstrate all test points at once rather than individually with an expensive meter.
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jw0752 over 10 years ago in reply to Problemchild

Thanks John,
If you make one I think it would look better on one of your plexiglass creation stands. I would have preferred plexiglass but I seem to have better luck with wood.
John
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Problemchild over 10 years ago in reply to jw0752

Im doing a new revision of that board I'll mention this to shabaz no doubt we'll see a load of these in use soon
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Problemchild over 10 years ago in reply to jw0752

Im doing a new revision of that board I'll mention this to shabaz no doubt we'll see a load of these in use soon
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