Current Sensor Configuration (ACS712 etc.)

fastbeeAbout 4 min

Current Sensor Configuration (ACS712 etc.)

1. Overview

Current sensors convert the current in a wire into a proportional voltage signal through the Hall effect. ESP32 collects this voltage through ADC, then converts it to actual current value through linear calibration.

Supported Sensor Models

Model	Range	Sensitivity	Zero-Current Output
ACS712-5A	±5A	185 mV/A	VCC/2 (1.65V@3.3V)
ACS712-20A	±20A	100 mV/A	VCC/2 (1.65V@3.3V)
ACS712-30A	±30A	66 mV/A	VCC/2 (1.65V@3.3V)

Working Principle

ACS712 internal Hall sensor detects wire current
Output voltage = VCC/2 + current × sensitivity
ESP32 ADC collects output voltage (12-bit, 0~4095)
Software conversion: I = (V_adc - V_offset) / sensitivity

Features

10-time multi-sample averaging to reduce ADC noise
200ms minimum read interval cache
Lazy initialization, auto-configures ADC on first call
Supports custom calibration parameters (sensitivity, zero offset, reference voltage)

When debugging current modules, first calibrate zero-current output, then gradually apply load; if readings drift, prioritize checking common ground, reference voltage, ADC attenuation, and sampling average parameters.

2. Wiring Instructions

ACS712 Module              ESP32
┌─────────────┐
│  VCC        │───────── 5V (module power)
│  GND        │───────── GND
│  OUT        │───────── GPIO34 (ADC pin)
│  IP+ / IP-  │───────── Current passes through
└─────────────┘

Notes:
- ACS712 module requires 5V power, but OUT output range is 0~VCC
- ESP32 ADC input maximum is 3.3V; if module is powered at 5V, a voltage divider is needed
- Recommend using 3.3V powered ACS712 modules, or add a voltage divider circuit
- Recommend GPIO34/35/36/39 (input-only pins, best ADC performance)

3. Configuration

Method 1: Web Interface Configuration (Recommended)

Before saving current sensor configuration, verify ADC pin, zero offset, sensitivity, and range protection.

Step 1: Navigate to Peripheral Management Page

Open a browser and navigate to the ESP32 IP address
After logging in, click Peripheral Configuration in the left menu

Step 2: Add Current Sensor Peripheral

Click the Add Peripheral button

Fill in the configuration:

Field	Value	Description
Peripheral ID	`current_01`	Unique identifier
Name	`ACS712 Current Detection`	Display name
Peripheral Type	GPIO Analog Input (type: 15)	ADC collection
Pin Configuration	`34`	ADC pin (recommend 34-39)
Attenuation	`3`	11dB(0-3.3V)
Resolution	`12`	12-bit(0-4095)

Click Save

Step 3: Verify Configuration

Find the newly added peripheral in the peripheral list
Click the Enable toggle
Check real-time current data

💡 Tip: ACS712 modules recommend 3.3V power; 5V modules need a voltage divider

Method 2: JSON Configuration File Import

Current sensors use GPIO_ANALOG_INPUT (type ID=15) or ADC (type ID=26) type to configure pins.

Peripheral Configuration Example (ADC Pin)

{
  "id": "current_01",
  "name": "ACS712 Current Detection",
  "type": 15,
  "enabled": false,
  "pinCount": 1,
  "pins": [34, 255, 255, 255, 255, 255, 255, 255],
  "params": {
    "attenuation": 3,
    "resolution": 12,
    "sampleRate": 5
  }
}

Field Description

Field	Meaning	Values
type	Peripheral type	15 (GPIO_ANALOG_INPUT) or 26 (ADC)
pins[0]	ADC pin	34/35/36/39 (input only) or other ADC-capable pins
params.attenuation	Attenuation coefficient	0=0dB, 1=2.5dB, 2=6dB, 3=11dB(3.3V)
params.resolution	Resolution	9~12 bits

4. Peripheral Execution Integration

Current sensors collect data via ACTION_SENSOR_READ (actionType=19) with SensorCategory::SENSOR_CURRENT(7).

Web Interface Configuration Steps

Create Current Collection Rule

Switch to the Peripheral Execution Management tab
Click the Add Rule button
Configure timer trigger:
- Trigger Type: Timer Trigger
- Execution Interval: 10 seconds
Add action:
- Action Type: Sensor Read
- Target Peripheral: current_01
- Data Field: current
- Sensitivity: 0.100 (ACS712-20A)
- Zero Offset: 1.65
Enable Report Data After Execution
Click Save

Create Overcurrent Alarm Rule

Create a new rule
Configure event trigger:
- Trigger Type: Event Trigger
- Event ID: ds:current_01_current
- Comparison: Greater Than
- Comparison Value: 15.0 (A)
Add actions:
- Action 1: Turn off relay
  - Action Type: Low Level
  - Target Peripheral: relay_01
- Action 2: Trigger overcurrent event
  - Action Type: Trigger Event
  - Event ID: over_current
Click Save

💡 Tip: Sensitivity and zero offset must be calibrated based on actual sensor model

JSON Configuration Example

Current Collection Rule Configuration

{
  "id": "exec_current_read",
  "name": "Current Timed Collection",
  "enabled": false,
  "triggers": [
    {
      "triggerType": 1,
      "timerMode": 0,
      "intervalSec": 10
    }
  ],
  "actions": [
    {
      "targetPeriphId": "current_01",
      "actionType": 19,
      "actionValue": "{\"periphId\":\"current_01\",\"sensorCategory\":\"current\",\"dataField\":\"current\",\"sensorLabel\":\"Current\",\"unit\":\"A\",\"decimalPlaces\":3,\"sensitivity\":0.100,\"zeroOffset\":1.65,\"vRef\":3.3,\"adcMax\":4095}"
    }
  ],
  "reportAfterExec": true
}

actionValue Format

Current sensor actionValue uses JSON string to pass read target and calibration parameters:

{
  "periphId": "current_01",
  "sensorCategory": "current",
  "dataField": "current",
  "sensorLabel": "Current",
  "unit": "A",
  "decimalPlaces": 3,
  "sensitivity": 0.100,
  "zeroOffset": 1.65,
  "vRef": 3.3,
  "adcMax": 4095
}

Parameter	Description	Example
sensitivity	Sensitivity (V/A)	0.100 (ACS712-20A)
zeroOffset	Zero offset voltage (V)	1.65 (VCC/2@3.3V)
vRef	ADC reference voltage (V)	3.3
adcMax	ADC maximum value	4095

Overcurrent Alarm Rule

{
  "id": "exec_current_alarm",
  "name": "Overcurrent Alarm",
  "enabled": false,
  "triggers": [
    {
      "triggerType": 4,
      "eventId": "ds:current_01_current",
      "operatorType": 2,
      "compareValue": "15.0"
    }
  ],
  "actions": [
    {
      "targetPeriphId": "relay_01",
      "actionType": 1,
      "actionValue": ""
    },
    {
      "targetPeriphId": "",
      "actionType": 21,
      "actionValue": "over_current"
    }
  ],
  "reportAfterExec": true
}

5. Calibration Methods

Zero Calibration

Disconnect the measured current (no current flowing)
Read the ADC value and convert to voltage
This voltage is the offset value (theoretical value VCC/2)

Sensitivity Calibration

Pass a known current (e.g., measure with a multimeter)
Record the voltage corresponding to the ADC reading
sensitivity = (V_measured - offset) / I_known

Common Calibration Parameter Quick Reference

Sensor Model	sensitivity	offset	Description
ACS712-5A @3.3V	0.185	1.65	Highest sensitivity
ACS712-20A @3.3V	0.100	1.65	Most commonly used
ACS712-30A @3.3V	0.066	1.65	High current scenarios
ACS712-20A @5V+divider	0.100	1.0	Adjust offset by divider ratio

6. Notes

ADC Accuracy: ESP32 ADC has significant non-linear error; recommend determining parameters through actual calibration
Noise Suppression: Driver has built-in 10-time sampling average; can appropriately increase sample count
5V Modules: If module is powered at 5V, output may exceed 3.3V; must add voltage divider to protect ESP32
Wiring Distance: Keep analog signal lines as short as possible, away from interference sources
Safety Isolation: ACS712 has built-in isolation, but high-voltage/high-current scenarios still require safety attention
Power-On Stability: Sensor needs 5~10ms to stabilize after power-on; first read is already handled in the driver

7. FAQ

Q: Readings are not zero when no current flows?

ACS712 zero offset may deviate from theoretical value due to imprecise supply voltage
Obtain actual offset value through zero calibration

Q: Readings fluctuate significantly?

Caused by ADC noise; can add hardware filter capacitor (100nF between OUT and GND)
Software already does 10-time averaging, sufficient for most scenarios

Q: How to detect AC current?

ACS712 supports AC/DC detection
AC current requires sampling over a complete cycle and calculating RMS value
Recommend sampling rate ≥ 20 × power frequency (50Hz → 1000Hz)