Example 5: Relay Control

Experiment Overview

Control the on/off state of a relay via GPIO digital output, enabling switching of high-power devices (lights, motors, solenoid valves, etc.). Relays are the most commonly used actuators in IoT projects.

Hardware Wiring

Board Label	GPIO Pin	Connected Device
RELAY	GPIO25	Relay module (energize on HIGH)

Relay modules typically have optocoupler isolation, HIGH level signal energizes the relay (NO contact closes).

JSON Configuration Example

{
  "peripherals": [
    {
      "id": "relay_01",
      "name": "Relay",
      "type": 12,
      "enabled": false,
      "pins": [25],
      "params": {
        "initialState": 0
      }
    }
  ]
}

Peripheral Execution Linkage

Scenario 1: Remote On/Off Control (Platform Trigger)

Function: Control relay on/off 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 Relay 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 used as action parameters

Step 3: Configure Action

1. Click Add Action button

2. Fill in:

   • Action Type: Select HIGH Level or LOW Level
   • Target Peripheral: Select relay_01

3. Click Save button

Test Method:

Send via cloud platform:

• 1 or HIGH → Relay energizes
• 0 or LOW → Relay de-energizes

---

Scenario 2: Timed Switch (Timer Trigger)

Function: Automatically start device at 8 AM every day

Web Interface Configuration Steps

Step 1: Create Rule

1. Click New Rule
2. Fill in basic configuration:
   • Rule Name: Relay Timed 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 Timer Trigger	Execute by time
   Timer Mode	Select Daily Timer	Fixed time every day
   Time Point	08:00	8:00 AM

Step 3: Configure Action

1. Click Add Action button

2. Fill in:

   • Action Type: Select HIGH Level
   • Target Peripheral: Select relay_01

3. Click Save button

💡 Tip: You can create another rule to turn off the relay at 6 PM (18:00)

Notes

1. Safety Voltage: When controlling mains voltage (220V) with relays, always prioritize safety and ensure proper isolation
2. Back EMF: Relay coils generate reverse voltage when de-energized; modules typically have built-in flyback diodes
3. Initial State: Recommend initialState: 0, default off at power-on to prevent accidental energizing
4. Current Capability: ESP32 GPIO outputs 3.3V/12mA, requires transistor or module to drive relay
5. Contact Rating: Standard relay contacts rated at 10A/250VAC, use larger relays for higher loads