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: Red
Accuracy: 1%
Refresh speed: 200MS per time
Display mode: 3 digits digital tube
Measuring range: 3.3-30V
Working current: Less than 20mA
Operating temperature: -10 °c - 65 °c
Red: Power Supply +, Measure Voltage +, (3.3 - 30V DC)
Black: Power Supply -, Measure Voltage -
Size: 27 * 14 * 9mm / 1.06 * 0.56 * 0.38in
Weight:3g / 0.1oz
Package size: 9.1 * 5.9 * 0.9cm / 3.6 * 2.3 * 0.38in
Package weight: 3g / 0.1oz

Note: Please connect the red wire to the positive pole and the black wire to the negative pole.
Package List:

1* Digital Voltmeter Panel