LamaPLC: Allegro ACS758 Hall-effect linear current sensors

The provided part numbers refer to specific models within the Allegro ACS758 series of Hall-effect linear current sensor integrated circuits (ICs), which primarily differ in their current-sensing range, sensitivity, and operating temperature range.

• Supply Voltage: 3.0 to 5.5 V.
• Internal Conductor Resistance: Ultra-low 100 µΩ, providing minimal power loss.
• Bandwidth: Typically 120 kHz.
• Zero Current Output: For these bidirectional (“B”) models with a 5V VCC, the output voltage is typically VCC/2 (2.5V) when no current is flowing.

Low power

• VCC: Power supply input (3.0V to 5.5V).
• GND: Ground connection.
• OU1: Direct analog signal from the sensor.
• OU2: Buffered signal through an onboard op-amp (often a Texas Instruments LM358 or similar) to reduce noise and drive longer cables.

Power path

• IP+: Current input.
• IP-: Current output.

Directionality: For bidirectional (“B”) models, current can flow in either direction. For unidirectional (“U”) models, current must flow from IP+ to IP- for a positive voltage increase.

This code reads a bidirectional sensor (such as the models you listed) and computes the DC current. It assumes a 5V Arduino and that the sensor is powered by 5V.

Select the mVperAmp value based on your specific ACS758 model:

• 050B: 40 mV/A
• 100B: 20 mV/A
• 150B: 13.3 mV/A
• 200B: 10 mV/A

const int sensorPin = A0;      // Pin connected to CJMCU-758 OUT
int mVperAmp = 40;             // Change to 20, 13.3, or 10 based on model
int ACSoffset = 2500;          // 2.5V (VCC/2) is the 0A midpoint for bidirectional sensors
 
void setup() {
  Serial.begin(9600);
}
 
void loop() {
  // 1. Read raw ADC value (0-1023)
  int rawValue = analogRead(sensorPin);
 
  // 2. Convert raw value to voltage in mV
  // 5000mV / 1024 ADC steps = 4.88mV per step
  double voltage = (rawValue / 1023.0) * 5000; 
 
  // 3. Subtract offset and divide by sensitivity to get Amps
  double current = (voltage - ACSoffset) / mVperAmp;
 
  Serial.print("Raw: "); Serial.print(rawValue);
  Serial.print(" | Voltage(mV): "); Serial.print(voltage);
  Serial.print(" | Current(A): "); Serial.println(current, 2);
 
  delay(500);
}

Key Considerations

• Calibration: The quiescent offset (voltage at 0 Amps) is theoretically 2500 mV but often varies slightly due to power supply noise or stray magnetic fields. Measure the voltage at 0 A, and update the ACSoffset in your code for improved accuracy.
• 3.3V Microcontrollers: If using an ESP32 or Arduino Due, you must use a voltage divider on the output to drop it below 3.3V, or use a 3.3V reference in your calculations (the sensitivity will also be lower).
• Averaging: To reduce jitter, take 10–100 samples in your loop and compute the mean.

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