how to connect a third-party 4–20 ma analog sensor to the rak sensor hub

The RAK2560 Sensor Hub is a modular device that connects multiple sensors to a single LoRaWAN network node. It is designed to work easily with official RAKwireless sensors for quick and reliable data transmission.

For use cases that require other sensor types, the Sensor Hub also supports third-party 4–20 mA analog sensors through the generic Probe IO adapter. This allows integrators to connect various analog-output devices common in industrial and environmental monitoring.

To demonstrate the integration process, this guide provides step-by-step instructions for connecting a Huamo RG202011170 water pressure sensor, covering:

• Hardware setup and wiring
• Power requirements
• Sensor configuration via WisToolBox

Requirements

• RAK2560 Sensor Hub
• Generic Probe IO
• A power supply
• WisToolBox
•  Smartphone with NFC
• Third-party 4-20 mA sensor, with:
  • Wiring/connection diagram
  • Communication parameters
  • Register description

Gather the Third-Party 4-20 mA Sensor Specifications

Before connecting the water pressure sensor to the RAK2560 Sensor Hub, it is imperative to review the sensor’s datasheet. Accurate setup depends on having complete technical specifications.

Electrical Parameters

The 4-20 mA sensors translate measured values into a direct current (DC) signal. To ensure proper operation with the Sensor Hub, configure the device based on:

• Output signal type
• Measurement range
• Power requirements

For example, the Huamo RG202011170 water pressure sensor outputs a 4–20 mA signal and has a pressure range of 0 to 100 kPa. It requires a 12–24  VDC supply for reliable operation.

Here’s the full product specifications, taken from the manufacturer’s datasheet:

Connection Diagram

The sensor cable connects to the Sensor Probe IO using screw terminals. If the sensor has a pre-installed connector, you’ll need to remove it to access the individual wires.

Most 4-20 mA sensors typically use a 2- or 3-wire configuration. The Huamo RG202011170 uses a 3-wire setup:

• Power (+V)
• Ground (GND)
• Signal Output

Figure 1: Three-wire wiring diagram

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 measurement range and output type

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

Connect the 4-20 mA 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 the Terminals
Locate the two screw terminals and refer to the pin labels printed on the side of the enclosure for correct terminal assignment.

Figure 2: Sensor Probe IO

3.Prepare and Connect the Wires

Using the sensor’s datasheet, match each wire to the correct pin based on the signal type. A 4–20 mA sensor uses only three terminals. Use the wire color references from the datasheet and the Sensor Hub screw terminal description to ensure correct alignment.

Figure 3: Probe IO and 4 - 20mA 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 4: 4-20 mA sensor to Sensor Hub Probe IO connection

Configure the 4-20 mA 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 been configured, it will display only the standard IO options. 

To configure the connected water pressure sensor, refer to the instructions below: 

1. Navigate to the Analog Input: 4-20 mA tab in WisToolBox.

Figure 5: Analog Input: 4-20 mA tab

2. Configure the analog input data interface parameters, and set the following:

• • Name: WaterPressure
  • Offset: 0.000000
  • Min Value: 0 kPA
  • Max Value: 160 kPA

Figure 6: Analog input data interface parameters

3. In the Unit drop-down menu, select Pressure for the water pressure sensor data, then click SAVE SELECTION.

Figure 7: Select the sensor type and save

4. Once all 4-20 mA settings have been configured and saved, press REMOVE SENSOR PROBE to forcibly disconnect the Probe IO.

Figure 8: 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 9: New sensor value

5. 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 Huamo water pressure sensor type RG202011170 used in this tutorial:

AT Command Reference for the 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 Huamo water pressure sensor type RG202011170 content may look like this:

2. Save this file as WPA.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 10: Import the sensor file

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

Figure 11: 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 email or message with the sensor profile and copy the sensor profile.

Figure 12: Copy the WPA.json code

6. Return to the WisToolBox window. When the pop-up appears, click APPLY to proceed.

Figure 13: Click APPLY to save the configuration

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

Figure 14: 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 15: 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 4-20 mA 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 23:03