Example 13: ADC Analog-to-Digital Conversion

Experiment Overview

Read analog voltage values via ADC (Analog-to-Digital Converter), converting 0~3.3V analog signals to digital values. ESP32 has two ADC modules (ADC1: 8 channels, ADC2: 10 channels), with resolution up to 12 bits (0~4095).

Hardware Wiring

Board Label	GPIO Pin	Connected Device
ADC	GPIO34	Potentiometer/Analog sensor output
ADC	GPIO36	Analog signal input

GPIO34-39 are input-only pins, best suited for ADC acquisition. ADC2 is unavailable when WiFi is active.

JSON Configuration Example

{
  "peripherals": [
    {
      "id": "adc_01",
      "name": "ADC Analog Input",
      "type": 15,
      "enabled": false,
      "pins": [34],
      "params": {}
    }
  ]
}

You can also use a dedicated ADC type for more precise configuration:

{
  "id": "adc_precise",
  "name": "ADC Precision Acquisition",
  "type": 26,
  "enabled": false,
  "pins": [36],
  "params": {
    "attenuation": 3,
    "resolution": 12,
    "sampleRate": 0
  }
}

ADC Attenuation Parameters

attenuation	Range	Precision
0	0~1.1V	Highest
1	0~1.5V	High
2	0~2.2V	Medium
3	0~3.3V	Lower

Peripheral Execution Linkage

Scenario: Voltage Monitoring Alarm (Poll Trigger)

Function: Detect ADC voltage every second, trigger buzzer alarm when voltage exceeds threshold (3000mV)

Web Interface Configuration Steps

Step 1: Ensure buzzer peripheral is configured

• Peripheral ID: buzzer_gpio
• Type: GPIO Output

Step 2: Create Rule

1. Click Peripheral Execution in the left menu
2. Click New Rule button
3. Fill in basic configuration:
   • Rule Name: Over-Voltage Alarm
   • Report Data: ✅ Enable
   • Enabled: ✅ Enable

Step 3: Configure Trigger (Poll Trigger)

1. Click Add Trigger button

2. Fill in trigger configuration:

   Field	Value	Description
   Trigger Type	Select Poll Trigger	Periodically detect condition
   Target Peripheral	Select adc_01	ADC analog input
   Poll Interval	1000	1000ms = 1 second
   Condition Expression	value > 3000	Voltage greater than 3000mV

Step 4: Configure Action

1. Click Add Action button

2. Fill in:

   • Action Type: Select HIGH Level
   • Target Peripheral: Select buzzer_gpio

3. Click Save button

Execution Flow:

Poll every 1 second
  ↓
Read ADC value (0-4095)
  ↓
Check: value > 3000?
  ↓ Yes
Buzzer alarm

ADC Attenuation Parameter Reference

attenuation	Range	Precision	Use Case
0	0~1.1V	Highest	Precision small voltage measurement
1	0~1.5V	High	Small voltage measurement
2	0~2.2V	Medium	Medium voltage measurement
3	0~3.3V	Lower	Full range measurement (default)

Notes

1. ADC2 Limitation: ADC2 (GPIO0,2,4,12-15,25-27) is unavailable when WiFi is enabled
2. Input Range: Exceeding 3.3V will damage the pin, voltage divider circuit needed
3. Precision: ESP32 ADC has non-linear errors, calibration needed for precise measurements
4. Input Impedance: ADC input impedance is high, but source impedance should not exceed 10kΩ
5. Sample Rate: Default single sample, sampleRate=0 means read on demand