Review on DaFuRui DC Voltage Display: Mini Digital Voltmeter with Reverse Polarity Protection and Accurate Pressure Measurement by Rob Bradford

I bought four of these kits to have enough voltmeters (plus spares) for a specific project - a pinball power driver test fixture that I designed and built. A house. My test rig uses 18 of these voltmeters to measure the control and output voltages for the 8 channels of the power driver, as well as the input and main supply voltages. I 3D printed the case/jig and used spring pins so I could just connect the power driver board, apply voltage and count volts on each channel. I was hoping that with 18 separate voltmeters I wouldn't have to individually test 16 different tiny test points on each power driver board. Everything didn't go according to plan. The specs posted here are a huge mistake. The 10mm height doesn't include the PCB height, so you can't mount them on 10mm centers without clearance. I had to redesign my mounting solution to center this 12mm instead of 10mm to accommodate 11.25-11.5mm PCB height + wobbly PCB alignment. Also, the mounting holes on the board are 29mm on center (instead of 26mm) and the full width of the board is 34mm (instead of 30mm). Another additional measurement is the Z-height of the white rectangle above the PCB, which varies widely from device to device due to common alignment issues, but ranges from 5.75mm to 7.5mm. These dimensions don't match the advertised dimensions, except for the whitest box, which measures 10mm x 22.6mm. Too bad I didn't know the exact dimensions before I started designing and printing. As for accuracy, this is both good and terrible. First, good. Even with 18 voltmeters I was able to connect them all to the same power supply and adjust the resistors so they all read the same and matched my professional voltmeter with little variation. Good. There is some drift when you have voltages that go from low to high, which means you can set the meter to 5V very accurately, but then you might get inaccurate readings at 40V. Set it to 40V , and your 5V readings will be off. Typically this drift is in the 1-2 volt range depending on the voltage delta, but I didn't need it to be super accurate, so I'm not deducting asterisks for that. If you're measuring voltage in a narrow range, this shouldn't be a problem. However, if you are measuring voltages from 3.3V to 100V with a single meter, this drift will be a problem. After I had completely set up the test bench, I encountered a completely unexpected problem. A voltmeter works great when it has direct access to the main power line. But in my test fixture, 8 voltmeters are connected to a very low current portion of my power driver circuitry. These meters measure the voltage between two separate power supplies at a point between the 47kΩ and 93kΩ resistors so that it shows only the tiniest trickle of amperes (about 0.5 milliamps). Using my professional voltmeter it shows the voltage accurately (i.e. 38V or 25V depending on the on/off circuit). But as soon as I connected one of those little voltmeters to it, the voltage changed completely! Instead of 38V and 25V it shows 26V and 19V! The best I can say is that these voltmeters draw too much current on the signal line and actively influence the measurement result. If you are only measuring the main power supply then this is not a problem. However, this makes these blocks totally unsuitable for measuring low current control signal voltages. Worse, the change in signal voltage is actually enough to trigger the circuit to turn on the power driver's output MOSFET. It is therefore not only a question of a misinterpretation of the voltages, but also of an influence on the circuit under test. So after all the hours of designing, printing and assembling the test bench, I still have to manually measure 8 points on each PCB because these voltmeters can measure tiny voltages or currents. Yes, I know I'm pretty much the only person on the planet who has crazy claims like this, so I doubt my review will help anyone. If it helps you, cheers brother!