how to build an rs485 soil sensor with wisblock and rui3

This tutorial demonstrates how to set up a sensor node using WisBlock modules that can communicate over RS485 with a "7-in-1" soil sensor.

For agricultural applications, it is often necessary to operate independently of a permanent power supply. The sensor node described in this guide runs on a 3200mAh battery, which is recharged by a solar panel during the day.

The application supports two different soil sensor products:

• Sensor 1 Tested and Verified: "No-Name" VEM SEE SN-3002-TR-ECTHNPKKPH-N01 sensor
• Sensor 2 Not Tested and Verified: GEMHO 7-in-1 Soil Sensor with RS485

The 12V power supply required by the soil sensor is generated using a WisBlock 12V booster module.

Requirements

Soil Sensors

• VEM SEE SN-3002-TR-ECTHNPKKPH-N01

• GEMHO 7 in 1 Soil Sensor

WisBlock modules & enclosure:

• RAK3172 Evaluation Board
  • RAK19007 WisBlock Base Board
  • RAK3372 WisBlock Core module with STM32WLE5
  • (Alternative) RAK4631 WisBlock Core module with nRF52840
• RAK5802-M WisBlock RS485 module (modified variant)
• RAK19002 WisBlock 12V booster for supply of soil sensor
• Unify Enclosure 150x100x45 with Solar Panel
• 3200 mAh battery

Hardware Assembly

Assembly is performed using the standard mounting plate of the Unify Enclosure. Sensor connections are made with the 5-pin IP65 connector of the Unify Enclosure with Solar Panel. The antenna used is a Blade Antenna with a gain of 2.3 dBi.

Figure 1: (Left) Finished prototype; (Right) Soil Sensor

Modbus/RS485 Wiring Diagram

The device utilizes the Unify Enclosure measuring 150mm x 100mm x 45mm, equipped with a solar panel and standard openings for the LoRa® antenna, as well as a waterproof 5-pin connector. The four wires from the soil sensor are connected to a 5-pin plug that fits into the enclosure's 5-pin connector.

Figure 2: RS485 Wiring Diagram

Firmware

The firmware is based on the basic RUI3-RAK5802-Modbus-Master code, with adjustments made for the RS485 sensor in use. The source code can be found in the GitHub repository RUI3-RS485-Soil-Sensor.

To ensure accurate sensor readings, the sensor is powered on for 5 minutes before data is collected. This allows the sensor sufficient time to complete its readings and calculations.

Custom AT Commands

Send Interval

The Send interval for the sensor values can be configured using a custom AT command. The interval time is specified in seconds.

ATC+SENDINT? - Command definition

ATC+SENDINT,: Set/Get the interval sending time values in seconds 0 = off, max 2,147,483 seconds
OK

ATC+SENDINT=? - Get current send interval in seconds

ATC+SENDINT=3600
OK

ATC+SENDINT=3600 - Get current send interval to 3600 seconds == 1 hour

ATC+SENDINT=3600
OK

Sensor Test

Sensor connection can be tested with a custom AT command.

ATC+STEST? - Command definition

ATC+STEST,R*W: Read sensor
OK

ATC+STEST=? - Start sensor test

ATC+STEST=?
OK

The output of the command is:

• Sensor found

> atc+stest=?
Sensor Power Up
OK
+EVT:Sensor Values: M:22.10-T:25.70-pH:3.00-C:140.0

The values measured are soil humidity (M), temperature (T), pH value (pH), and conductivity (C). If the sensor is not in the soil, these values may be zero or nonsensical.

• Sensor not found

> atc+stest=?
Sensor Power Up
OK
+EVT:Error reading sensor

• Sensor reading already active

This may be because a manually started test has not yet completed, or a scheduled automatic sensor reading is currently in progress.

> atc+stest=?
AT_BUSY_ERROR

Visualization of the Sensor Data

To visualize the sensor data, the following (free) extensions are used:

• InfluxDB

  There are two options:

  1. Use the InfluxDB Cloud Serverless

  2. Install InfluxDB on your own server

In this case, Option 2 was chosen. InfluxDB is installed on a VPS.

• Grafana

  Also has two options:

  1. Use Grafana Cloud

  2. Install Grafana on your own server

Option 2 was selected. Grafana is also running on the same VPS.

• LoRaWAN Server Integration

  ChirpStack V4 was used to integrate InfluxDB with the LoRaWAN server. It is installed on the same VPS, alongside InfluxDB and Grafana.

Register the Sensor Nodes in the LoRaWAN Server

No detailed instructions for this section. These steps are common for connecting sensor nodes to a LoRaWAN server.

1. Set up the LoRaWAN server and connect the gateway(s) to it. Ensure that both the LoRaWAN server and the gateway(s) are configured for the same LoRaWAN region.

2. Create an application on the LoRaWAN server. Register the sensor nodes within the application and provide the following details:

• For OTAA: DevEUI, AppEUI, and AppKey.
• For ABP: DevAddress, AppSKey, and NwSKey.

3. Verify that the application on the LoRaWAN server is receiving data from the sensor nodes.

Figure 3: ChripStack Raw Data Received

Set Up the Codec in ChirpStack

To store data in the InfluxDB database, a payload decoder must be configured in ChirpStack. Payload decoders are defined within the Device Profiles. 

1. In the web UI, navigate to the Device Profiles and then select the Codecs.

Figure 5: ChripStack Codec Tab

3. RAKwireless has a ready-to-use JavaScript decoder for Chirpstack. You can get it from the RAKwireless_Standardized_Payload GitHub repository.

Figure 6: GitHub Repository Payload Codec

4. Click the Raw button to view the JavaScript code as plain text. Then, copy the entire JavaScript code and paste it into the Chirpstack Codec functions text field.

Figure 7: ChripStack Codec Field

5. To verify that the decoder is working, return to the device page in ChirpStack and navigate to the Events tab. This section displays the received data packets.

6. Click the up button next to a received packet to view the decoded payload.

Figure 8: ChripStack Events Tab

Installation of InfluxDB and Grafana

The installation of InfluxDB and Grafana is accomplished using a Docker YAML file. It is important to note the local IP addresses of both applications, which can be obtained through the Portainer management tool.

Figure 10: Portainer Management Tool List of Applications

Figure 10: InfluxDB Main Menu

2. Create two tokens using the GENERATE API TOKEN button: one for Chirpstack and one for Grafana. These tokens will be required in the next steps.

Figure 11: InfluxDB API Create Tokens Menu

3. Create an organization and a bucket to store the sensor data.

Figure 12: InfluxDB Create Organization

4. Use RAKwireless for both the organization and the bucket, and click CREATE.

Figure 13: InfluxDB Create Organization

Figure 14: ChripStack Applications Select InfluxDB

6. Fill out the connection details for the InfluxDB database.

• This installation uses InfluxDB v2.
• The API endpoint is the IP address of the InfluxDB Docker instance obtained from Portainer.
• The organization and bucket are those we created in InfluxDB.
• The token is the access token we generated in InfluxDB.

8. Choose InfluxDB as the new connection type.

Verify Data Arrival in the Database

11. Open the InfluxDB web UI, navigate to the Data Explorer, and select the appropriate bucket. The easiest way to locate the data is to use the DevEUI of the soil sensors as the first filter.

12. Next, use _measurement as the second filter. You will now see all the data received from the soil sensor.

// Cayenne LPP Channel numbers per sensor value
#define LPP_CHANNEL_BATT 1 // Base Board
#define LPP_CHANNEL_MOIST 2
#define LPP_CHANNEL_TEMP 3
#define LPP_CHANNEL_COND 4
#define LPP_CHANNEL_PH 5
#define LPP_CHANNEL_NITRO 6
#define LPP_CHANNEL_PHOS 7
#define LPP_CHANNEL_POTA 8
#define LPP_CHANNEL_SALIN 9
#define LPP_CHANNEL_TDS 10

// Add temperature level to payload
g_solution_data.addTemperature(LPP_CHANNEL_TEMP, coils_n_regs.sensor_data.reg_2 / 10.0);

Set Up Grafana Dashboard

16. Open the Grafana web UI and navigate to Home > Dashboards. Next, click the New button and select New dashboard.

Figure 23: Grafana New Dashboard

17. In the next window, select the option to add a visualization.

Figure 24: Add new visualization in Grafana

18. Then select InfluxDB as the data source.

Figure 25: Grafana Select InfluxDB Data Source

19. A new window showing the visualization details will open. Paste the Flux query you previously copied from InfluxDB Data Explorer into the query field.

Figure 26: Paste Flux query from InfluxDB

There are several options for modifying the presentation of the data. In this case, only the Panel Title has been changed to Soil Temperature. 

For more information on the other options, refer to the Grafana documentation.

Figure 27: Change the Panel Title

20. Click the Apply button to add the visualization to the new dashboard.

Figure 28: Apply the changes made

The panel displaying soil temperature is now shown on the dashboard.

Figure 29: Soil temperature Grafana dashboard

21. To add the other sensor values, you can use one of two methods:

• Select the Add option from the top menu, choose Visualization, and repeat the steps above for the new sensor value.

Figure 30: Add new visualization in the dashboard

• Duplicate the existing visualization, changing only the title and the Flux query.

Figure 31: Grafana Duplicate Option

If Duplicate is chosen, open the visualization menu and select Edit.

Figure 32: Edit the duplicated visualization in Grafana dashboard

22. In the edit window, only two changes need to be made: the source in the Flux query and the title. 

• The source should be updated to the moisture level (device_frmpayload_data_humidity_2).
• The title should be changed to Soil Moisture.

Figure 33: Change visualization name to Soil Moisture

Other sensor values can be added to the Dashboard in the same way. When all sensor values are visualized, the Dashboard will appear as follows:

Figure 34: Overall visualization dashboard in Grafana

Appendix

Soil Sensor Registers

• VEM SEE SN-3002-TR-ECTHNPKKPH-N01 Soil Sensor register setup

Assembly Guide

• Required Parts

• WisBlock Assembly (Location of Modules)

Bernd Giesecke Electronics Engineer, 23 years of experience in industrial and automotive HW and SW R&D. Supporting Arduino open-source community since 2014.

Updated July 16, 2025 06:05