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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