Example 11: PWM Breathing LED

Experiment Overview

Control LED brightness via PWM (Pulse Width Modulation) output, creating a breathing effect from dim to bright and back. PWM simulates analog voltage output by adjusting the duty cycle.

Hardware Wiring

Board Label	GPIO Pin	Connected Device
D1	GPIO15	LED (PWM dimming)

ESP32 has 16 PWM channels, almost any GPIO can output PWM signals.

JSON Configuration Example

{
  "peripherals": [
    {
      "id": "pwm_breath",
      "name": "Breathing LED-PWM",
      "type": 17,
      "enabled": false,
      "pins": [15],
      "params": {
        "pwmChannel": 0,
        "pwmFrequency": 5000,
        "pwmResolution": 8,
        "defaultDuty": 0
      }
    }
  ]
}

Parameter Description

Parameter	Description	Recommended Value
pwmChannel	PWM channel number (0-15)	0
pwmFrequency	Frequency (Hz), high freq = no flicker	5000
pwmResolution	Resolution (bits), 8-bit = 0~255	8
defaultDuty	Initial duty cycle	0

Peripheral Execution Linkage

Scenario 1: Remote Brightness Control (Platform Trigger)

Function: Control LED brightness (0-255) via cloud platform commands

Web Interface Configuration Steps

Step 1: Create Rule

1. Click Peripheral Execution in the left menu
2. Click New Rule button
3. Fill in basic configuration:
   • Rule Name: Remote Brightness Control
   • Report Data: ✅ Enable
   • Enabled: ✅ Enable

Step 2: Configure Trigger

1. Click Add Trigger button

2. Fill in trigger configuration:

   Field	Value	Description
   Trigger Type	Select Platform Trigger	Receive cloud platform commands
   Operator	Select Set Mode	Received data as action parameters

Step 3: Configure Action

1. Click Add Action button

2. Fill in:

   • Action Type: Select Set PWM
   • Target Peripheral: Select pwm_breath

3. Click Save button

Test Method:

Send via cloud platform:

• 0 → Brightest (common-anode LED)
• 128 → 50% brightness
• 255 → Dimmest (off)

---

Scenario 2: Auto Breathing Effect (Timer Trigger + Script)

Function: Use script for automatic breathing effect (fade in → fade out cycle)

Web Interface Configuration Steps

Step 1: Create Rule

1. Click New Rule
2. Fill in basic configuration:
   • Rule Name: LED Breathing Light
   • Report Data: ✅ Enable
   • Enabled: ✅ Enable

Step 2: Configure Trigger

1. Click Add Trigger button

2. Fill in trigger configuration:

   Field	Value	Description
   Trigger Type	Select Timer Trigger	Execute script on timer
   Timer Mode	Select Fixed Interval	Fast refresh
   Interval Time	20	20ms (smooth breathing effect)

Step 3: Configure Action (Script)

1. Click Add Action button

2. Fill in:

   • Action Type: Select Command Script
   • Action Params:

   var d=getVar('breath_duty',0);
   var dir=getVar('breath_dir',1);
   d+=dir*5;
   if(d>=255){d=255;dir=-1;}
   if(d<=0){d=0;dir=1;}
   pwmWrite('pwm_breath',d);
   setVar('breath_duty',d);
   setVar('breath_dir',dir);

3. Click Save button

Script Description:

Code	Description
getVar('breath_duty',0)	Get current duty cycle, default 0
getVar('breath_dir',1)	Get direction, 1=brightening, -1=dimming
d+=dir*5	Change by 5 levels each time
pwmWrite('pwm_breath',d)	Set PWM duty cycle
setVar(...)	Save variable for next use

⚠️ Note: Script executes every 20ms, consuming system resources, do not run multiple scripts simultaneously

Notes

1. Frequency Selection: LED dimming recommend 1kHz+ to avoid flicker, 5kHz is common
2. Resolution: 8-bit (256 levels) is sufficient for LED dimming, 12-bit (4096 levels) for fine control
3. Channel Conflict: Different pins can share the same PWM channel (same frequency and duty cycle)
4. Active Low: Puzhong board LEDs are common-anode, duty=0 is brightest, duty=255 is dimmest
5. Multi-PWM: ESP32 supports 16 independent PWM outputs simultaneously