Modern embedded systems often need to measure current—whether for power monitoring, motor control, battery management, or smart energy meters. The ACS712 current sensor module offers an easy, accurate, and safe way to measure current in both AC and DC circuits using microcontrollers like Arduino, ESP32, Raspberry Pi, and others.
1. What is the ACS712 Current Sensor?
The ACS712 is a Hall-effect-based current sensor integrated circuit (IC) manufactured by Allegro Microsystems. It can measure both AC and DC current without breaking the main current path or having direct electrical contact.
Unlike shunt resistors, which measure current by dropping voltage directly, the ACS712 uses the Hall Effect—meaning:
👉 It senses magnetic fields created by the current flowing through its internal conductor.
👉 Converts magnetic field changes into a proportional voltage output.
👉 Provides electrical isolation and increased safety.
2. How Does the ACS712 Work?
The core principle is Hall Effect:
- Current flows through a built-in conductor inside the ACS712.
- The current generates a magnetic field around it.
- A Hall sensor measures that magnetic field.
- The sensor outputs an analog voltage proportional to the current.
📌 With no current, the output sits at about VCC/2 (approx. 2.5V if powered at 5V).
📌 When current flows, the output swings above or below 2.5V depending on direction (AC or DC).
This makes it ideal for microcontrollers with analog input capabilities like Arduino.
3. Versions & Specifications
The ACS712 comes in multiple current ranges. The most common are:
| Model | Max Current | Sensitivity |
|---|---|---|
| ACS712-05B | ±5 A | 185 mV/A |
| ACS712-20A | ±20 A | 100 mV/A |
| ACS712-30A | ±30 A | 66 mV/A |
Key Features
- Supply voltage: 5V (typically)
- Output voltage: Analog (centered at ~2.5V)
- AC & DC current measurement
- Electrical isolation between load and sensor
- Low power consumption
4. Interfacing ACS712 with Arduino
Materials Needed
| Component | Purpose |
|---|---|
| Arduino UNO | Microcontroller |
| ACS712 Sensor Module | Current sensing |
| USB Cable | Power & communication |
| Load (e.g., lamp, motor) | To measure current |
| Power supply (AC/DC based on load) | Load power |
Wiring Diagram
ACS712 → Arduino
-------------------
VCC → 5V
GND → GND
OUT → A0 (analog input)
Then place the load on the ACS712 current path (the high-current line passes through the sensor).
5. Arduino Code Example
Below is a simple sketch to read current and display it on the Serial Monitor:
// ACS712 Example Code
int sensorPin = A0;
float sensitivity = 0.185; // 185mV per Amp (for 5A module)
void setup() {
Serial.begin(9600);
}
void loop() {
int sensorValue = analogRead(sensorPin);
float voltage = (sensorValue / 1023.0) * 5.0;
float current = (voltage - 2.5) / sensitivity;
Serial.print("Current: ");
Serial.print(current);
Serial.println(" A");
delay(500);
}
Explanation
- Read analog voltage from the sensor.
- Convert to actual voltage (0–5V range).
- Subtract 2.5V zero reference.
- Divide by sensitivity to get current in amps.
6. Calibration & Accuracy
- The ACS712 output has noise — use averaging to get stable readings.
- Ambient temperature can affect accuracy — use temperature compensation if needed.
- Always calibrate with known loads before final measurement.
7. Example Projects with ACS712
Project 1 — AC Current Measurement with Arduino
Objective: Measure AC current of a household device (lamp, fan, etc.) using ACS712 and display it on LCD.
Key Steps:
- Connect the AC load through ACS712.
- Read and sample voltage multiple times per AC cycle.
- Calculate RMS current.
- Display results on LCD or Serial Monitor.
Useful For: Energy monitoring, smart home dashboards.
Project 2 — DC Motor Current Monitoring
Objective: Monitor startup current and running current of a DC motor.
Highlights:
- Helps detect stall conditions (where motor draws max current).
- Useful in robotics and automation systems.
Project 3 — Battery Current Logging (Solar / UPS)
Objective: Log charging/discharging current of a battery bank.
Features:
- Works with solar panel systems.
- Can detect over-current and help control charging.
Project 4 — Overcurrent Protection System
Objective: Trigger a relay or buzzer when current exceeds a safe limit.
How It Works:
- Continuously read current.
- If current > threshold → trigger alert or switch off load.
8. Tips for Best Results
✔ Use short wires to reduce noise
✔ Add a filter capacitor at the output
✔ Use moving average in software
✔ Avoid placing sensor near motors or magnets
9. Pros & Cons of ACS712
Pros
✔ Works with AC & DC
✔ Electrical isolation
✔ Easy microcontroller interfacing
✔ Affordable
Cons
✖ Lower accuracy than high-end current sensors
✖ Sensitive to noise
✖ Requires calibration
10. Conclusion
The ACS712 current sensor remains one of the most accessible, versatile, and beginner-friendly current sensing modules for electronics projects. Whether you’re building power meters, battery monitors, motor controllers, or safety systems, the ACS712 lets you measure current safely and efficiently with platforms like Arduino.
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