how to connect a third-party rs485 sensor to the rak sensor hub

The RAK2560 Sensor Hub is designed to interface with multiple sensor types, enabling centralized data collection over a LoRaWAN network. While it works seamlessly with RAKwireless sensors, it can also be configured to support third-party devices, including RS485/Modbus sensors, via the Generic Probe IO adapter.

To illustrate the integration process, this guide outlines the steps for connecting a third-party Modbus RS485 soil sensor. The sensor used in this example is the VEMSEE SN-3002-TR-ECTHNPKPH-N01, a multi-parameter device commonly used in agricultural and environmental monitoring.

Requirements

• RAK2560 Sensor Hub
• Generic Probe IO
• A power supply
• WisToolBox
•  Smartphone with NFC
• Third-party RS485 sensor, with:
  • Wiring/connection diagram
  • Communication parameters
  • Register description

Gather the Third-Party RS485 Sensor Specifications

Before connecting the RS485 sensor to the RAK2560 Sensor Hub, review the sensor’s datasheet to ensure correct wiring, protocol settings, and power requirements. Accurate setup depends on having complete technical specifications.

Communication Parameters

Most RS485 devices support multiple baud rates, with 9600 baud often used as a default. However, this is not consistent across manufacturers. The sensor in use defaults to 4800 baud, with 8 data bits, no parity, and 1 stop bit (8N1 configuration).

Figure 1: VEMSEE RS485 sensor basic communication parameters

Register Description

Each sensor defines its register map for data access. For this sensor, the relevant values are located in the first four registers. Additionally, scaling factors must be applied to convert raw register values into meaningful sensor data. These factors are required during setup to ensure accurate data interpretation.

Figure 2: VEMSEE RS485 sensor register address

Connection Diagram

The Sensor Probe IO uses a screw-terminal interface for sensor connections. If the sensor cable includes a pre-installed connector, it must be removed to expose the individual wires. 

RS485 devices typically use four wires: 

• Two  for power 
• Two for differential data (A/B)

Refer to the sensor’s datasheet to identify wire functions and ensure correct pin assignments.

Figure 3: RS485 sensor interface and wiring details

At this point, you should have all the essential information needed to wire the sensor to the Sensor Hub, including:

• The correct wiring diagram
• The sensor’s supply voltage requirements
• The register map and scaling factors
• The communication parameters (baud rate, data bits, parity, stop bits)

You can now proceed to connect the sensor wires to the Sensor Probe IO.

Connect the RS485 Sensor to the Sensor Hub Probe IO

To connect the sensor wires to the Probe IO, follow the steps below:

1. Open the Probe IO
Remove the four screws to open the lid and access the internal screw terminals.

2. Identify Terminals
Locate the two screw terminals and refer to the pin labels printed on the side of the enclosure.

Figure 4: Sensor probe IO

3. Prepare and Connect Wires
Using the sensor’s datasheet, match each wire to the correct pin. RS485 sensors require only four connections: two for power and two for differential data (A and B). 

Refer to the wire color codes in the sensor datasheet and the screw terminal labels on the Sensor Hub to ensure correct alignment. Secure all connections firmly.

Figure 5: Probe IO RS485 power and communication pins

4. Check and Finalize

Ensure no bare wires are exposed or touching adjacent terminals or the PCB. Then, close the Probe IO and connect it to the Sensor Hub.

Figure 6: RS485 sensor to Sensor Hub Probe IO connection

Configure the RS485 Sensor for the Sensor Hub in WisToolBox

Since the Generic Probe IO does not contain any predefined information about the connected sensor, you must configure both the connection parameters and sensor data settings manually using WisToolBox.

There are two ways to do this:

1. Manual Setup in WisToolBox: Configure the sensor directly by entering the parameters in the UI. 
2. Sensor Profile File Setup: Create a reusable sensor profile file that can be imported into WisToolBox and applied to the Probe IO.

Manual configuration is ideal for setting up a single sensor, such as for testing purposes. However, when deploying multiple units, using a sensor profile file is a more efficient and scalable option, allowing the same configuration to be applied consistently across all devices.

Manual Setup in WisToolBox

Once the generic Probe IO is connected to the Sensor Hub, it will be automatically detected in the WisToolBox as Generic Probe IO. If the Probe IO has not yet been configured, it will display only the standard IO options. 

To set up the connection to the soil sensor, refer to the instructions below:

1. Navigate to the RS485 Interface tab in WisToolBox.

Figure 7: RS485 Interface tab

2.Configure the RS485 data interface with the following parameters:

• • Baud Rate: 4800 baud
  • Data Bit: 8 bits
  • Parity Bit: None
  • Stop Bit: 1

Figure 8: RS485 configuration parameters

3. Open the Modbus Commands. Each sensor register requires a separate Modbus read command to retrieve its value. 

4. Select Command ID 1 to set up the reading of the sensor’s soil moisture values.

5. Update the Function Code, Start address, Data type, and Scale fields based on the information provided in the sensor datasheet. Set the following fields to:

Figure 9: Modbus Commands configuration

• Function code: Holding Register (for the sensor fields)
• Start address: 0000. It should match the register address listed in the sensor datasheet. From the sensor datasheet:

Figure 10: RS485 register address and content

• Data type: INT16_BE. Must match the standard size of a register.
• Scale: 0.1. It corresponds to the expanded 10 times comment in the datasheet.

Figure 11: Scale parameter

6. Enter the Device Address. This must match the Modbus used by the sensor.

According to the datasheet, the default address is 1. Most devices allow this address to be changed, which is essential when multiple sensors share the same RS485/Modbus bus. If the device uses a different address, enter the correct value in the Device Address field.

Figure 12: Sensor's address code description

7. The Unit field is a drop-down menu with all sensor types supported by the SensorHub. For the soil sensor moisture data, Moisture is the correct setting.

Figure 13: Sensor type options under Unit

8. Set Max wait (ms) to 5000 and Max retry to 2. These values are good starting points and can be increased if there are issues retrieving data from the sensor.

9. Enter a custom label in the Name field, and the Period (s) defines the data polling interval, which should be configured to suit the requirements.

10. Once all fields are adjusted, the Modbus command used to acquire the data is shown in the Modbus ADU field. 

11. If the sensor datasheet includes Modbus command examples, compare them to verify accuracy, then click APPLY to save the settings.

12. Repeat the process for additional sensor parameters:

• Command ID 2: Soil temperature
• Command ID 3: Soil conductivity
• Command ID 4: Soil pH

13. Once all RS485/Modbus read commands have been configured and saved using the APPLY button, forcibly remove the Probe IO from the Sensor Hub by clicking the REMOVE SENSOR PROBE button.

Figure 14: Temporarily remove the sensor probe 

The Probe IO will automatically reconnect with the new configuration. The new sensor values will now be visible in WisToolBox.

Figure 15: New sensor values

14. On the initial refresh, the sensor values might still display as 0. Click the FETCH DATA button to manually trigger a sensor read.

Sensor Profile File Setup for the Sensor Hub

The second method to configure custom sensors for the Sensor Hub is to create a sensor profile file.

This method not only simplifies configuration when deploying multiple identical sensors but also enables advanced control of the sensor’s power supply behavior.

Creating a Sensor Profile File

A profile file is a JSON format that defines the sensor configuration, containing five entries:

Here is the sensor profile file created for the VEMSEE RS485 soil sensor used in this tutorial:

Another sensor profile example for the 4-20 mA sensor. For more details, refer to the 4-20 mA Sensor to Sensor Hub guide.

AT Command Reference for Sensor Interface Setup

The following AT commands are used to set up the sensor interface, such as configuring power management, data interface settings. 

1. ATC+IO_PSM

Defines how the sensor’s power supply is managed. Two power mechanisms are available:

1. Always On: The sensor remains powered continuously.
2. Interval-Based Power: The sensor remains off until a reading is triggered. Power is then enabled for <SensorWarningTime> milliseconds before the data is read, after which the sensor is powered off again.

Parameters of the atc+io_psm command:

ATC+IO_PSM={PRB_ID}:<UartPSM>:<SensorPSM>:<SensorWarningTime>:<SensorVolt>:<method>

Example
Periodic power-off mode with 5-second sensor power on:

ATC+IO_PSM={ProbeID}:9:1:5000:0:1

2. ATC+IO_CFG

Defines the interface parameters.

ATC+IO_CFG={PRB_ID}:<if>:<value1>:...:<valueN>

For RS485, RS232, and SDI12, the value fields are:

ATC+IO_CFG={PRB_ID}:<if>:<baudrate>:<databit>:<stopbit>:<parity>

Example
RS485 connection with 4800 baud, 8 data bits, 1 stop bit, and no parity:

ATC+IO_CFG={PRB_ID}:RS485:4800:8:1:0

3. ATC+SNSR_CONF

Sensor rules for sending data packets

ATC+SNSR_CONF={PRB_ID}:<snsr_rule>:{SNSR_INTV}:<method>

Example
Periodic sending of data every 5 minutes:

ATC+SNSR_CONF={PRB_ID}:8:{SNSR_INTV}:1

4. ATC+IO_ADDPOLL

Definition of an RS485/Modbus register read command

ATC+IO_ADDPOLL={PRB_ID}:<if>:{TASK_ID2}:{DEV_ADDR}<reg_type><reg_addr><data_len>:<period>:{timeout>:{retry>:{data_type>:{scale>:{snsr_type>:{PROFILE_NAME}

Example
RS485/Modbus register read from device 0x01. It uses a holding register (03) with the following parameters:

• Register Address: 0
• Data Length: 1
• Poll Interval: 60 seconds
• Max Wait Time: 1000ms
• Max retries: 2
• Data Type: 16-bit unsigned integer
• Scale: 0.1
• Sensor Type: Moisture

AT command syntax:

ATC+IO_ADDPOLL={PRB_ID}:RS485:{TASK_ID1}:{DEV_ADDR}0300000001:60:1000:2:6:0.1:188:{PROFILE_NAME}

Parameter Details:

• {DEV_ADDR}: The RS485/Modbus address of the device. This is a 2-byte hexadecimal value, assigned when the sensor profile is imported.
• <reg_type>: Indicates the type of action to be performed on the Modbus. It occupies 2 bytes.

• <reg_addr>: The start address of the end device to read or write to. It occupies 4 bytes in hexadecimal value format.
• <data_len>: The number of registers or coils to read or write to. It occupies 4 bytes in hexadecimal format.

Sensor Types

5. ATC+IO_DECODE

Definition for DI, DO, and analog interface

ATC+IO_DECODE={PRB_ID}:<ifname>:<Channel>:<value1>:...:<valueN>

Values for the analog interface:

Example
Analog interface on channel 1, sensor type 130, max value 5, min value 0:

ATC+IO_DECODE={PRB_ID}:ai:1:130:5:0:{PROFILE_NAME}:1

Values for digital input:

Values for digital input:

6. ATC+PRB_DEL

Force removal of the Probe IO after setup. Probe IO will automatically reconnect with the new interface settings.

ATC+PRB_DEL={PRB_ID}

Importing a Sensor Profile File

Additional Requirement:

A text editor or viewer on the mobile phone that supports JSON files.

Preparation

1. Write a sensor profile and save it as a .json file. For example, the VEMSEE sensor content may look like this:

2. Save this file as VEMSEE.json and transfer it to your mobile phone. Alternatively, the file can be sent to the phone via email or a messaging app.

Import the Sensor Profile

1. Connect WisToolBox to the Sensor Hub and navigate to the Sensor Probe tab.

2. Open the Generic Probe IO section, scroll down to locate the IMPORT SETTINGS option, and click it.

Figure 16: Import the sensor file

3. A new window will appear, prompting a QR code scan or to open the RAKwireless URL.

Figure 17: Scan QR code

4. Keep the WisToolBox app page open in the background and switch to the text editor or viewer on your mobile phone.

5. Open the VEMSEE.json file and copy the entire text content.

Figure 18: Open the VEMSEE.json file

Figure 19: Copy VEMSEE.json code

6. Return to the WisToolBox window. When the pop-up appears, enter the RS485/Modbus device address 01, then click APPLY to proceed.

Figure 20: RS485/Modbus device address

WisToolBox will return to the main screen and show the import progress.

Figure 21: Applying commands in progress

After the Sensor Profile Import

Once the import is finished, the Probe IO will disconnect and reconnect automatically. After the reconnection, the new setup of the Probe IO with the soil sensor will be visible.

Figure 22: Probe IO new setup

On the first refresh, the sensor values might still be showing 0. Use the FETCH DATA button to manually trigger a sensor read.

The third-party RS485 sensor connected to the Probe IO and Sensor Hub is now ready to transmit data.

Bernd Giesecke Bernd is an Electronics Engineer and Product Manager at RAKwireless with 23 years of experience in industrial and automotive hardware and software R&D. He has been supporting the Arduino open-source community since 2014.

Updated June 03, 2025 23:08