This example demonstrates how to measure current using the ACS758 50A current sensor with an Arduino UNO. The code calculates both DC and AC current, and for AC signals it measures:

• Peak current
• RMS current
• Voltage
• Frequency

The ACS758 outputs 2.5V at 0A. The Arduino reads this offset using its 10-bit ADC.

• Current Sensor: The ACS758 outputs a voltage proportional to current. 2.5V = 0A, deviation represents positive or negative current.
• DC and AC Detection: DC produces a stable level; AC oscillates. AC is recognized using zero-cross detection around the 2.5V level.
• RMS, Peak, and Frequency Calculation: For AC, the Arduino computes peak and RMS current and determines signal frequency from zero-cross timing.

/*
 * Arduino UNO with ACS758 50A Current Sensor.
 * Measures DC current, AC RMS current and frequency.
 * © 2024 Copyright Peter I. Dunne, all rights reserved.
 * The ADC is 10 bit, accuracy is limited. Use proper equipment for precision.
 * Released under the Mozilla Public License.
 */

const int currentPin = A0;      // Current sensor connected to A0
const float sensorOffset = 2.5; // 2.5V corresponds to 0A
const float maxCurrent = 50.0;  // ACS758 measures up to 50A
const float VRef = 5.0;         // Arduino reference voltage
const int maxADCValue = 1023;   // 10-bit ADC resolution
const int threshold = 512;      // Midpoint of ADC (0A)
const unsigned long interval = 500;

unsigned long lastZeroCrossingTime = 0;
float sumSquaredCurrent = 0;
int sampleCount = 0;
bool polarity = false;
bool zcd = false;
unsigned long previousACmillis = 0;
int zcp = 512;
unsigned long previousMillis = 0;
float frequency = 0;

void setup() {
    Serial.begin(115200);
    Serial.println("Arduino DMM current measurement, by Peter I. Dunne, ©2024");
    Serial.println("Released under the Mozilla Public License");
    Serial.println("https://jazenga.com/educational");
    Serial.println("Demonstrates ADC system for AC and DC current measurement.");
}

void loop() {
    int adcValue = analogRead(currentPin);
    float voltage = (adcValue / float(maxADCValue)) * VRef;
    float current = (voltage - sensorOffset) * (maxCurrent / sensorOffset);

    unsigned long currentMillis = millis();
    unsigned long currentMicros = micros();

    if (polarity != adcValue > zcp) {
        polarity = adcValue > zcp;

        if (polarity) {
            zcp = threshold - 10;
            previousACmillis = currentMillis;
            unsigned long period = currentMicros - lastZeroCrossingTime;
            lastZeroCrossingTime = currentMicros;

            if (period > 0) {
                frequency = 1000000.0 / period;
            } else {
                zcp = threshold + 10;
            }

            zcd = true;
        }
    }

    if ((currentMillis - previousACmillis) <= interval) {
        sumSquaredCurrent += current * current;
        sampleCount++;

        if (zcd && polarity) {
            if ((currentMillis - previousMillis) >= interval) {
                previousMillis = currentMillis;

                float rmsCurrent = sqrt(sumSquaredCurrent / sampleCount);

                Serial.print("RMS Current: ");
                Serial.print(rmsCurrent, 2);
                Serial.print(" A, Frequency: ");
                Serial.print(frequency, 2);
                Serial.println(" Hz");

                sumSquaredCurrent = 0;
                sampleCount = 0;
            }
        }
    } else {
        if ((currentMillis - previousMillis) >= interval) {
            previousMillis = currentMillis;
            Serial.print("DC Current: ");
            Serial.print(current, 2);
            Serial.println(" A");
        }
    }
}

• Current Measurement: ACS758 outputs 2.5V at 0A. Arduino converts ADC readings to amperes using the sensor’s transfer function.
• DC/AC Detection: If the signal moves above and below 2.5V, it is considered AC. A stable level is DC.
• Peak & RMS Current: RMS is computed from squared sample averages and represents effective AC current.
• Zero-Crossing Detection: Each transition through 2.5V marks a zero crossing. Timing between crossings gives frequency in Hz.