Example 33: Light Sensor

Experiment Overview

A photoresistor (LDR) changes resistance based on light intensity — the stronger the light, the lower the resistance. A voltage divider circuit converts resistance changes to voltage changes, which are read by the ADC. Suitable for automatic lighting, light-controlled curtains, and similar applications.

Hardware Wiring

Board Label	GPIO Pin	Connected Device
AO	GPIO34	Light sensor module analog output

The stronger the light, the lower the analog output value; the weaker the light, the higher the value.

JSON Configuration Example

{
  "peripherals": [
    {
      "id": "light_01",
      "name": "Light Sensor",
      "type": 15,
      "enabled": false,
      "pins": [34],
      "params": {}
    }
  ]
}

Peripheral Execution Linkage

Scenario 1: Auto Light On at Dusk (Polling Trigger)

Feature: Automatically turn on light when darkness is detected (ADC > 3000)

Web UI Configuration Steps

Step 1: Ensure LED Peripheral is Configured

• Peripheral ID: led_d1
• 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: Auto Light On at Dusk
   • Report Data: ✅ Enabled
   • Enable: ✅ Enabled

Step 3: Configure Trigger (Polling Trigger)

1. Click Add Trigger button

2. Fill in trigger configuration:

   Field	Value	Description
   Trigger Type	Select Polling Trigger	Periodic condition check
   Target Peripheral	Select light_01	Light sensor
   Polling Interval	5000	5 seconds
   Condition Expression	value > 3000	Low light threshold

Step 4: Configure Action

1. Click Add Action button

2. Fill in:

   • Action Type: Select LOW (common-anode LED)
   • Target Peripheral: Select led_d1

3. Click Save button

---

Scenario 2: Auto Light Off at Dawn (Polling Trigger)

Feature: Automatically turn off light when dawn is detected (ADC < 1000)

Configuration Steps:

1. Create rule, name: Auto Light Off at Dawn
2. Trigger configuration:
   • Trigger Type: Select Polling Trigger
   • Target Peripheral: Select light_01
   • Polling Interval: 5000
   • Condition Expression: value < 1000 (bright light threshold)
3. Action configuration:
   • Action Type: Select HIGH (common-anode LED off)
   • Target Peripheral: Select led_d1
4. Click Save

Light Sensor Value Reference

Light Condition	ADC Value	Description
Bright (Sunlight)	<500	Bright environment
Indoor Light	1000-2000	Normal indoor
Dusk	2000-3000	Dim light
Dark Night	>3000	Very dark

Notes

1. Response Speed: Photoresistors respond slowly (~tens of milliseconds); not suitable for fast-changing detection
2. Temperature Effect: Temperature changes slightly affect resistance
3. Threshold Calibration: Thresholds differ across environments; on-site tuning required
4. Non-linearity: The resistance-to-light relationship of photoresistors is non-linear