Pasted

//https://gist.github.com/locy/7022857
//https://gist.githubusercontent.com/locy/7022857/raw/1a3ff02c1ad74ddd1f4765555a64532e356b704e/ACS712.ino
 
int VQ;
int ACSPin = 0;
 
void setup() {
  Serial.begin(115200);
  VQ = determineVQ(ACSPin); //Quiscent output voltage - the average voltage ACS712 shows with no load (0 A)
  delay(1000);
}
 
void loop() {
  Serial.print("ACS712@A2:");Serial.print(readCurrent(ACSPin),3);Serial.println(" mA");
  delay(150);
}
 
int determineVQ(int PIN) {
  Serial.print("estimating avg. quiscent voltage:");
  long VQ = 0;
  //read 5000 samples to stabilise value
  for (int i=0; i<5000; i++) {
    VQ += analogRead(PIN);
    delay(1);//depends on sampling (on filter capacitor), can be 1/80000 (80kHz) max.
  }
  VQ /= 5000;
  Serial.print(map(VQ, 0, 1023, 0, 5000));Serial.println(" mV");
  return int(VQ);
}
 
float readCurrent(int PIN) {
  int current = 0;
  int sensitivity = 185.0;//change this to 100 for ACS712-20A or to 66 for ACS712-30A
  //read 5 samples to stabilise value
  for (int i=0; i<5; i++) {
    current += analogRead(PIN) - VQ;
    delay(1);
  }
  current = map(current/5, 0, 1023, 0, 5000);
  return float(current)/sensitivity;
}