Features:Digital voltmeter with precision automatic adjustment.It only has two wires、 you can connect to the measure power directly.It has the polarity reverse protection、 won't damage the meter.Minimum input: DC3.3 (Below this voltage、 it will show measurement inaccurately、 or doesn't show).Maximum Input: DC30V (Please do not exceed 30V、 otherwise、the meter would be damaged).No need of power supply.Specifications:Light color: BlueAccuracy: ?à1%Refresh speed: 200MS per timeDisplay mode: 3 digits digital tubeMeasuring range: 3.3 - 30VWorking current: Less than 20mAOperating temperature: -10 ??c - 65 ??cRed: Power Supply +、 Measure Voltage +、 (3.3 - 30V DC)Black: Power Supply -、 Measure Voltage-Size: 27 * 14 * 9mm / 1.06 * 0.56 * 0.38inWeight: 3g / 0.1ozPackage size: 9.1 * 5.9 * 0.9cm / 3.6 * 2.3 * 0.38inPackage weight: 3g / 0.1ozNote: Please connect the red wire to the positive pole and the black wire to the negative pole.Package List:1 * Digital Voltmeter Panel"