This is a mini DC voltmeter with LED display. Thanks to the small dimension it can be easily integrated into your project. It has three wires (yellow, red and black) and can measure up to 100V. The voltmeter can measure up to 100V. If the actual measured voltage is higher than 3.5V and is lower than 30V, you can also merge the red and yellow wires and simplify the wiring like this. In this case, the measured voltage will also work as the power supply for the voltmeter. This voltmeter has been calibrated before leaving the factory. However, if you want to get better accuracy, you can calibrate it by spinning the potentiometer on its back. Spinning the potentiometer clock-wise will reduce the displayed voltage value.