L-com Multifunction Air Quality Sensor Module (MODBUS)

Product Description

A photograph shows the SRAQ-D701 module, a compact electronic circuit board. It features various electronic components, including integrated circuits, resistors, capacitors, and connectors. A prominent blue housing is visible, along with red and black wires connecting different parts of the board. The module is labeled 'SRAQ-D701 0004'.

The SRAQ-D701 is a comprehensive air quality sensor module which combines CO2, laser dust, temperature, humidity, TVOC, and formaldehyde detection. It is developed for integration into air purifiers, air quality monitors, and custom enclosures. The SRAQ-D701 provides real-time concentration values via Modbus-RTU output. It offers good stability and is well suited for applications where TVOC and particulate matter concentrations are a concern.

Features

• Detects multiple pollutants: CO2, dust, etc.
• Modbus output
• High reliability and good stability
• High accuracy & fast response
• Compact design for easy integration

Applications

• Office and commercial buildings
• Factory floors
• Laboratories
• HAVC industry
• General air quality monitoring
• Smart home systems

Technical Parameters

Detection Parameters and Resolution: The CO2 value and formaldehyde value measured by the module are equivalent values of TVOC; please pay attention when using or purchasing.

Notes

1. Working voltage: 5 ± 0.2 VDC
2. Working environment: Working temperature 0~50 °C, Working humidity: 15% RH – 90% RH (no condensation)
3. Working environment: Temperature range -20~60 °C, Humidity: 5% RH – 95% RH (no condensation)
4. Communication method: Modbus RTU – RS485
5. Preheating time: 10-15 minutes; the longer the power-on time, the more stable the data will be.

Mounting Diagrams

The module is designed for board mounting. The technical drawing shows mounting hole details: diameter of 2 mm with a pitch of 11.5 mm. Key dimensions are provided in inches and millimeters for precise placement.

Wire Definition

The port connector type is an XH2.54mm pitch 4-pin terminal connector, mounted 90° vertically to the PCB.

Communication Protocol

The module hardware supports both serial TTL communication interface and RS485 communication interface. Users should select the appropriate communication method based on the module interface type purchased.

RS485 Interface Communication Protocol

Serial port parameters: (9600/8/N/1) ModBus-RTU 485. The factory default address of the module is 0x01. Baud rate: 9600, Check bit: none, Stop position: 1 bit. Return data time: <300ms. The reading speed cannot exceed 350ms.

Read Address Command

This command is used to read the current address of the module. The example shows a 'Receive' command structure with fixed fields, function code (17), and a request for address information, followed by an 'Answer' structure containing the firmware version (xx) and current address (yy).

Modify Address Command

This command allows modification of the module's address, which can be changed from 0 to 254. The factory default is 0x01. The example illustrates sending a command with the current address, function code (06), and the new desired address (zz).

Read Data Command

This command is used to read sensor data. It requires the current address, function code (03), the starting register address (00 MM), and the number of sensors required (00 NN). The 'Answer' structure contains the data length and the sensor data itself.

Register Address Mapping:
00 00: eCO2
00 01: TVOC
00 02: CH2O
00 03: PM2.5
00 04: Humidity
00 05: Temperature
00 06: PM10

Description of Data Reading

The minimum number of sensors to read is 00 01, and the maximum is 00 07. When the register address (MM) is 00, the maximum data length (NN) can be 07, allowing all sensor values to be read. If NN is 01, only CO2 data is read. The address at the front of the register can read subsequent sensor data when the data length is increased, but addresses at the back cannot read data from preceding addresses.

How to Read a Frame of Data

To read sensor data, for example, if the module address is 0x01, send command `01 03 00 00 00 07 04 08` to read seven types of sensor data. The returned data frame structure includes header, function code, data length, and sensor data (CO2, TVOC, CH2O, PM2.5, Humidity, Temperature, PM10) along with CRC check bytes.

Data Frame Example:
Byte[0] (Header): 0x01
Byte[1] (Function Code): 0x03
Byte[2] (Data Length): 0x0E
Byte[3]-Byte[4] (CO2 Data): CO2_H, CO2_L
Byte[5]-Byte[6] (TVOC Data): TVOC_H, TVOC_L
Byte[7]-Byte[8] (CH2O Data): CH2O_H, CH2O_L
Byte[9]-Byte[10] (PM2.5 Data): PM2.5_H, PM2.5_L
Byte[11]-Byte[12] (Humidity Data): Hum_H, Hum_L
Byte[13]-Byte[14] (Temperature Data): Tem_H, Tem_L
Byte[15]-Byte[16] (PM10 Data): PM10_H, PM10_L
Byte[17]-Byte[18] (CRC16 Check): CRC16_L, CRC16_H

Calculation Method of Each Sensor Data

• CO2 (ppm) = CO2_H * 256 + CO2_L
• TVOC (ug/m³) = (TVOC_H * 256 + TVOC_L) / 10
• CH2O (ug/m³) = (CH2O_H * 256 + CH2O_L) / 10
• PM2.5 (ug/m³) = PM2.5_H * 256 + PM2.5_L
• PM10 (ug/m³) = PM10_H * 256 + PM10_L
• Positive temperature (°C) = (Temperature_H * 256 + Temperature_L) / 10
• Example: T = (0x0110) / 10 = 272 / 10 = 27.2 °C

Negative Temperature (°C)

Method 1: Directly convert to a signed int type (e.g., T = 0xFFBF / 10 = -65 / 10 = -6.5 °C).
Method 2: If the value is greater than 0x7FFF (32767), it is a negative number. T = (0xFFBF - 65536) / 10 = (65471 - 65536) / 10 = -65 / 10 = -6.5 °C.

Humidity (%RH)

Humidity (%RH) = (Humidity_H * 256 + Humidity_L) / 10

Example: T = (0x02AD) / 10 = 685 / 10 = 68.5 %RH

Note: If mg/m³ is required as the unit, use the conversion formula: 1mg/m³ = 1000 ug/m³.

The length of the CRC check byte is 17 (bytes Byte[0]~Byte[16]). Select A001 or 8005 in reverse order.

Matters Needing Attention

• Avoid contact with organic solvents (including silica gel and other adhesives), paints, pharmaceuticals, oils, and high-concentration gases.
• The module must not be subjected to excessive shock or vibration.
• Do not apply this module to systems involving personal safety.
• Do not install the module in a strong air convection environment.

CRC Check Calculation Method

This section describes the CRC check function for generating CRC. It defines the parameter description (arr_buff: array to be verified, len: length of data to be verified) and the return parameter (CRC as an unsigned int type, with the high byte first and low byte second). The provided C code snippet outlines the `CRC_Compute` function logic.