Controls temperature, ventilation, and operating modes via Modbus thermostat.
Overview
The Smart Temp Australia SMT-131 is a Modbus RTU thermostat for HVAC control. This template reads actual temperature, setpoint, and operating status, and allows writing setpoint and operating status to manage heating, cooling, and ventilation modes remotely.
Key readings
Actual Temperature
Setpoint
Operating Status
Available commands
Setpoint
Operating Status
Use cases
Monitor actual room temperature and setpoint on a live dashboard across multiple HVAC zones.
Remotely adjust the temperature setpoint for a customer site without a truck roll.
Create an alert when actual temperature deviates more than 2 degrees from the setpoint for over 15 minutes.
Switch operating status between heating, cooling, and ventilation modes from the ModbusCloud platform.
Log temperature trends over time to identify inefficient heating or cooling patterns in commercial buildings.
Group multiple SMT-131 thermostats on one dashboard for centralized multi-zone climate management.
Installation
1Wire the SMT-131 to the ModbusCloud gateway (MCG or MLP series) using a twisted-pair RS-485 cable, connecting A, B, and GND terminals.
2Set the Modbus slave address on the SMT-131 to a unique value that does not conflict with other devices on the same bus.
3Confirm the baud rate on the SMT-131 is set to 19200 to match the template default.
4Import the SMT-131 template in the ModbusCloud platform and assign it to the corresponding gateway and slave address.
5Verify communication by checking that actual temperature, setpoint, and operating status values appear on the dashboard.
6Test write functionality by changing the setpoint or operating status from the platform and confirming the thermostat responds.
Things to watch for
01
The gateway cannot communicate with the SMT-131. What should I check?
Verify that the RS-485 wiring is correct, with A, B, and GND connected properly. Confirm the baud rate is set to 19200 on both the thermostat and the gateway. Ensure the Modbus slave address matches the address configured in the template.
02
Temperature values appear incorrect or unrealistically high. What is wrong?
All registers are uint16. Make sure the template is not interpreting the value as a signed integer or applying an incorrect scaling factor. Check the SMT-131 documentation for the decimal point position of temperature values.
03
I can read values but writing the setpoint does not work. Why?
Confirm that the setpoint register at address 8 is being written with a Modbus function code that supports single or multiple register writes. Also verify that the thermostat is not in a locked mode that prevents remote setpoint changes.
04
Can I use multiple SMT-131 thermostats on the same RS-485 bus?
Yes. Assign each SMT-131 a unique Modbus slave address. Create a separate template instance in ModbusCloud for each thermostat, matching the correct address.
Registers (3)
3 read / 2 write
Name
Address
Function
Type
Unit
Access
Actual Temp
10
FC03
uint16
R
Setpoint
8
FC03
uint16
R/W
Operating Status
6
FC03
uint16
R/W
Working with Modbus in your projects?
ModbusCloud is the hardware-plus-software platform that installers use to monitor, visualise and control Modbus devices from one portal. This template is one of hundreds you can use right away.
