Example 54: Modbus Sensor Device Configuration

Scenario Overview

Connect external sensor devices (such as temperature/humidity transmitters, air quality sensors, soil sensors, etc.) via Modbus RTU protocol to achieve industrial-grade data acquisition and remote monitoring.

Applicable Devices

Device Type	Typical Model	Measured Parameters
Temp/Humidity Transmitter	SHT20/SHT30 RS485	Temperature, Humidity
Air Quality Sensor	PM2.5/CO2 RS485	PM2.5, CO2 concentration
Soil Sensor	Soil 3-in-1 RS485	Temperature, Humidity, Conductivity
Light Sensor	BH1750 RS485	Illuminance (Lux)

Hardware Wiring

RS485 Interface Connection

ESP32 Pin	TTL-to-RS485 Module	Description
GPIO 16 (TX)	TXD	Serial transmit
GPIO 17 (RX)	RXD	Serial receive
GPIO 4 (optional)	DE/RE	Direction control (half-duplex)
3.3V	VCC	Power
GND	GND	Ground

RS485 bus connection:

ESP32 ──── TTL-to-RS485 ──── A/B Bus ──┬── Sensor 1 (Address 1)
                                        ├── Sensor 2 (Address 2)
                                        └── Sensor 3 (Address 3)

A 120Ω terminating resistor is recommended at the end of the RS485 bus.

Data Reporting Format

Each sensor data is reported independently:

[
  {"id": "modbus_temp_humi", "value": "temperature:25.3,humidity:60.5"},
  {"id": "modbus_air", "value": "pm25:35,co2:450"},
  {"id": "modbus_soil", "value": "soil_temp:22.1,soil_moisture:45.3,soil_ec:120"}
]

Peripheral Execution Linkage

Scenario 1: Temperature Exceeds Limit Triggers Fan (Poll Trigger)

Function: Turn on fan relay when temperature exceeds 30°C

Web Interface Configuration Steps

Step 1: Ensure Peripherals are Configured

• Modbus Temp/Humidity: modbus_temp_humi
• Fan Relay: relay_fan (GPIO output)

Step 2: Create Rule

1. Click Peripheral Execution in the left menu
2. Click Add Rule button
3. Fill in basic configuration:
   • Rule Name: High Temp Fan On
   • Report Data: ✅ Enabled
   • Enable: ✅ Enabled

Step 3: Configure Trigger (Poll Trigger)

1. Click Add Trigger button

2. Fill in trigger configuration:

   Field	Value	Description
   Trigger Type	Select Poll Trigger	Timed condition detection
   Target Peripheral	Select modbus_temp_humi	Modbus Temp/Humidity
   Data Field	temperature	Temperature field
   Operator	>	Greater than
   Threshold	30	30°C
   Poll Interval	5000	5 seconds

Step 4: Configure Action

1. Click Add Action button

2. Fill in:

   • Action Type: Select HIGH
   • Target Peripheral: Select relay_fan

3. Click Save button

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Scenario 2: CO2 Exceeds Limit Alarm (Poll Trigger)

Function: Trigger buzzer alarm when CO2 concentration exceeds 1000ppm

Configuration Steps:

1. Create a rule, name: CO2 Exceed Alarm
2. Trigger configuration:
   • Trigger Type: Select Poll Trigger
   • Target Peripheral: Select modbus_air
   • Data Field: co2
   • Operator: >
   • Threshold: 1000
   • Poll Interval: 10000
3. Action configuration:
   • Action Type: Select HIGH
   • Target Peripheral: Select buzzer1 (buzzer must be configured in advance)
4. Click Save

Debugging Tips

1. Address Scan: Use the built-in Modbus scan feature to confirm slave addresses first
2. Baud Rate Matching: Ensure all devices use the same baud rate (common: 9600/4800)
3. Register Confirmation: Consult device manual to confirm register start address and data format
4. Bus Isolation: When debugging, connect devices one by one; connect all only after confirming communication is normal

Notes

1. Bus Length: RS485 bus maximum 1200m, but recommend not exceeding 100m in practice
2. Device Count: Maximum 32 slaves per bus; add repeater if exceeded
3. Polling Conflict: Stagger the interval of multiple devices to avoid simultaneous requests
4. Data Format: Register formats may differ by manufacturer (big-endian/little-endian, integer/float); adjust scale per manual
5. Power Isolation: In industrial environments, recommend electrical isolation for RS485 interface to avoid ground loop interference