Module Description: This module is based on a resistive divider design principles, can reduce the voltage of the input terminal connection five times, analog input voltage up to 5V, then the input voltage of the voltage detection module can not be greater than 5V × 5 = 25V (3.3V if used system, the input voltage does not exceed 3.3Vx5 = 16.5V). Because AVR chips used in 10 AD, so the simulation resolution of this module is 0.00489V (5V / 1023), so the voltage detection module detects minimum input voltage is 0.00489V × 5 = 0.02445V. Parameters: Input voltage range: DC0-25V Voltage detection range: DC0.02445V-25V Voltage analog resolutions: 0.00489V DC Input: positive terminal connected to VCC, GND negative pole Output interface: "+" then 5 / 3.3V, "-" then GND, "s" then the AD pin Reference Code: #include int val11; int val2; void setup () { pinMode (LED1, OUTPUT); Serial.begin (9600); Serial.println ("Emartee.Com"); Serial.println ("Voltage:"); Serial.print ("V"); } void loop () { float temp; val11 = analogRead (1); temp = val11 / 4.092; val11 = (int) temp; // val2 = ((val11% 100) / 10); Serial.println (val2); delay (1000); }