These mini voltmeters are really tiny. One of them would be a great addition to any variable power supply project.
The voltmeters are from an hong kong seller. All the logic to convert the input signal and display it has been mounted underneath a 3-digit led display, not much larger than my thumb. Each module is something around $2.
You just connect the module to the power rails you want to measure and it will get both its power supply and the measurement from there, so it’s only 2 wires that go where you want to sample the voltage, which has to be between 3.3V and 30V.
They are very similar to those sold here by adafruit.
Mini voltmeter test
I tried to hook the modules up to an arduino, just to use its regulators and these were the readings i’ve got:
So there is 1% error on the 5V sample and 6.4% on the 3.3V sample, provided the Arduino regulators are accurate enough. I’d say not bad even if the modules could not be used as a main instrument.
The voltmeters have also been tested with a professional power supply. The outcome is that voltages on the low side of the allowed range turn out to be higher, while the opposite happens on the high side of the scale, where we had 30V show up as 28.5V.
The values start to get accurate around 5V and precise at 12V, confirming both my original Arduino measurements and the original purpose of the mini voltmeter: measure the output of automotive batteries.