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tMDS-16 - Temperature meter with Modbus interface

tMDS-16 - Temperature meter with Modbus interface

tMDS-16 is a temperature measurement module with Modbus RTU interface. It features two independent 1-Wire buses, each capable of connecting up to 8 DS18B20 temperature sensors, allowing for a total of 16 sensors.

Measurement data is made available via Modbus registers, which include both the current sensor readings and corresponding offset values used for calibration. The calibration ensures accurate and consistent measurements across all connected sensors.

The tMDS-16 is primarily designed to function as an extension module for LK4 or LK3.5+ devices (also compatible with LK3.9), enabling scalable and distributed temperature monitoring.
A ready-to-use configuration file for these devices is available, allowing for quick and hassle-free integration.

By default, the device uses Modbus Slave ID 1, which can be changed via the serial console on the USB.

Basic features

Technical specifications

Parameter Value
Power supply 5 - 12 V DC (connector)
5 V (USB)
Sensor support Up to 2 × 8 DS18B20 sensors
Interfaces 1-Wire: 2 buses via RJ12 and 3-position terminal block,
Modbus RTU (RS485),
Serial (over USB; 115200 baud)
Dimensions 74 × 40 × 28 mm (without DIN handle)
Weight 44 g

Integration with LK

The tMDS-16 integrates seamlessly with LK4 and LK3.5+ devices. It can be powered directly from the LK controller using its 5 V and GND outputs. Then, connect it—either alone or together with other Modbus devices—to the LK’s Modbus A+ and B− terminals to establish communication.

Once connected, configure a custom Modbus module on the LK using the ready-to-use configuration preset available in the Downloads section. You can easily modify this preset to read only the parameters you need, such as selected temperature sensors or calibration offsets.

Firmware update

To update the firmware, the device must be placed into bootloader mode. In this mode, the device appears as a mass storage device named RPI-RP2 when connected to a PC. Simply copy the new firmware file to that storage. After the upload, the device will automatically restart and resume normal operation with the new firmware.

Enabling bootloader mode

You can enable bootloader mode in one of two ways:

Firmware files are available in the Downloads section.

Basic configuration with function button

The function button on the tMDS-16 provides a convenient way to perform basic setup actions without connecting the device to a computer.

The button is placed near the edge of the board opposite the side with the USB port and the Modbus and power supply connectors.
A status LED next to the button indicates which function will be executed, depending on how long the button is held.

How it works

When holding the button, the status LED will blink to signal the selected action:

Press Duration LED Feedback Action Triggered
< 2 seconds 1 short blink shortly after press update_sensors – detect and assign connected sensors
2 - 5 seconds 2 blinks after 2 seconds set_offsets – auto-calibrate all sensors (offsets saved automatically)
5 - 10 seconds 3 blinks after 5 seconds reset_sensors – clear all sensor assignments and offsets
> 10 seconds No action cancelled (button held too long)

To execute a function, release the button immediately after the desired blink pattern appears.
If the button is held for too long (>10 seconds), no action will be taken.

ℹ️ For more advanced configuration and diagnostics, use the USB console as described in the next section.

Advanced configuration

To modify the settings, you will need to connect the tMDS-16 to a computer via USB. The device can be powered through USB, so no additional power connections are necessary.

Required software

To establish a connection with the board, you’ll need an application that can handle serial communication. Popular choices include:

Example Configuration Process

  1. List Available Ports
    Run pyserial-ports to list the available COM ports before connecting the device. The output might look like:

    COM1
COM3
COM15
COM16
COM17

  2. Connect the Device
    Plug in the tMDS-16 and run the command again. The new COM port (e.g., COM11) will represent the connected device.

  3. Connect to tMDS-16
    Use the following connection parameters:

    • Baud rate: 115200
    • Byte size: 8 bits
    • Parity: None
    • Stop bits: 1

    Example command:

    pyserial-miniterm COM11 115200

  4. Send Commands
    Once connected, you can issue commands to the device. Each command must be followed by the Enter key. A useful command is ? or help, which provides a list of all available commands (described below).

Command list

Command Description
address? | a? Get the Modbus address (Slave ID).
address=X | a=X Set the Modbus address. Parameters: X - address to set, number <1, 255>.
offsetX? | oX? Get the value of offset for DSX. Parameters: X - DS number <1, 16>.
offsetX=Y | oX=Y Set the offset value. Parameters: X - DS number <1, 16>; Y - value of offset, number <-3_276.8, 3_276.7>.
idX? | iX? Get the value of ID for DSX. Parameters: X - DS number <1, 16>.
idX=Y | iX=Y Set the ID value. Parameters: X - DS number <1, 16>; Y - value of ID, string AA:AA:AA:AA:AA:AA:AA:AA.
update_sensors | us Update list of sensors - detect and assign sensors.
set_offsets | so Automatically calculate offsets for all active sensors.
reset_sensors Reset sensors IDs and their offsets.
read_sensors | rs Read the sensors readings.
save_config | sc Save configuration to Flash memory. It should be called after changing the Modbus address and offsets.
read_registers | rr Read Modbus register values.
read_definitions | rd Read Modbus register definitions (name, address, type).
bootloader Reboot the device into bootloader mode to update the firmware. When connected to a computer, it will appear as a storage device named RPI-RP2, to which you should copy the firmware file with the extension uf2. Then the device will reboot into normal operation mode.
restart Restart the device.
verbose=X | v=X Turn on or off verbose mode, which displays more messages.
help | ? Display this help message with a list of available commands.

Common use cases

Below are practical examples of how to configure and use the tMDS-16 via the console.

Changing the Modbus Slave address

When multiple Modbus devices share the same bus, each device must have a unique address.

Example:

address=5
save_config

This sets the device address to 5 and stores the configuration in Flash memory.

Calibrating sensor readings manually

If a sensor shows a consistent offset compared to a reference thermometer, you can manually adjust it using the offsetX=Y command.

Example:

offset3=-0.5
save_config

This applies a correction of −0.5 °C to sensor DS3.

Auto-calibrating all sensors

If all connected sensors are placed in the same known temperature environment, you can automatically calculate offsets.

set_offsets

The device will measure the current readings and compute offsets so that all sensors report the same value.

This command automatically saves the calculated offsets to Flash memory.

Reading sensor values

To print current readings from all sensors:

read_sensors
Detecting sensors

If sensors are added or removed, refresh the sensor list:

update_sensors

To completely reset the stored sensor assignments and offsets:

reset_sensors
Inspecting Modbus registers

To inspect the Modbus register definitions and their current values:

read_definitions
read_registers

These commands are useful for diagnostics or when integrating the device with external Modbus software.

Modbus registers

Below is the list of Modbus registers available in the device.
The content corresponds to the output of the read_definitions command and includes register names, addresses, types, and divisors.

| Name                           | Addr | Type   | Func         | Divisor |
| ------------------------------ | ---- | ------ | ------------ | ------- |
| uptime                         | 3000 | uint32 | 0x04 (IREG)  |         |
| ds1                            | 3002 | int32  | 0x04 (IREG)  |      10 |
| ds2                            | 3004 | int32  | 0x04 (IREG)  |      10 |
| ds3                            | 3006 | int32  | 0x04 (IREG)  |      10 |
| ds4                            | 3008 | int32  | 0x04 (IREG)  |      10 |
| ds5                            | 3010 | int32  | 0x04 (IREG)  |      10 |
| ds6                            | 3012 | int32  | 0x04 (IREG)  |      10 |
| ds7                            | 3014 | int32  | 0x04 (IREG)  |      10 |
| ds8                            | 3016 | int32  | 0x04 (IREG)  |      10 |
| ds9                            | 3018 | int32  | 0x04 (IREG)  |      10 |
| ds10                           | 3020 | int32  | 0x04 (IREG)  |      10 |
| ds11                           | 3022 | int32  | 0x04 (IREG)  |      10 |
| ds12                           | 3024 | int32  | 0x04 (IREG)  |      10 |
| ds13                           | 3026 | int32  | 0x04 (IREG)  |      10 |
| ds14                           | 3028 | int32  | 0x04 (IREG)  |      10 |
| ds15                           | 3030 | int32  | 0x04 (IREG)  |      10 |
| ds16                           | 3032 | int32  | 0x04 (IREG)  |      10 |
| ds1_readErrors                 | 3034 | uint32 | 0x04 (IREG)  |         |
| ds2_readErrors                 | 3036 | uint32 | 0x04 (IREG)  |         |
| ds3_readErrors                 | 3038 | uint32 | 0x04 (IREG)  |         |
| ds4_readErrors                 | 3040 | uint32 | 0x04 (IREG)  |         |
| ds5_readErrors                 | 3042 | uint32 | 0x04 (IREG)  |         |
| ds6_readErrors                 | 3044 | uint32 | 0x04 (IREG)  |         |
| ds7_readErrors                 | 3046 | uint32 | 0x04 (IREG)  |         |
| ds8_readErrors                 | 3048 | uint32 | 0x04 (IREG)  |         |
| ds9_readErrors                 | 3050 | uint32 | 0x04 (IREG)  |         |
| ds10_readErrors                | 3052 | uint32 | 0x04 (IREG)  |         |
| ds11_readErrors                | 3054 | uint32 | 0x04 (IREG)  |         |
| ds12_readErrors                | 3056 | uint32 | 0x04 (IREG)  |         |
| ds13_readErrors                | 3058 | uint32 | 0x04 (IREG)  |         |
| ds14_readErrors                | 3060 | uint32 | 0x04 (IREG)  |         |
| ds15_readErrors                | 3062 | uint32 | 0x04 (IREG)  |         |
| ds16_readErrors                | 3064 | uint32 | 0x04 (IREG)  |         |
| version_major                  | 3100 | uint16 | 0x04 (IREG)  |         |
| version_minor                  | 3101 | uint16 | 0x04 (IREG)  |         |
| version_patch                  | 3102 | uint16 | 0x04 (IREG)  |         |
| address                        | 4000 | uint16 | 0x03 (HREG)  |         |
| offset1                        | 4001 | int32  | 0x03 (HREG)  |      10 |
| offset2                        | 4003 | int32  | 0x03 (HREG)  |      10 |
| offset3                        | 4005 | int32  | 0x03 (HREG)  |      10 |
| offset4                        | 4007 | int32  | 0x03 (HREG)  |      10 |
| offset5                        | 4009 | int32  | 0x03 (HREG)  |      10 |
| offset6                        | 4011 | int32  | 0x03 (HREG)  |      10 |
| offset7                        | 4013 | int32  | 0x03 (HREG)  |      10 |
| offset8                        | 4015 | int32  | 0x03 (HREG)  |      10 |
| offset9                        | 4017 | int32  | 0x03 (HREG)  |      10 |
| offset10                       | 4019 | int32  | 0x03 (HREG)  |      10 |
| offset11                       | 4021 | int32  | 0x03 (HREG)  |      10 |
| offset12                       | 4023 | int32  | 0x03 (HREG)  |      10 |
| offset13                       | 4025 | int32  | 0x03 (HREG)  |      10 |
| offset14                       | 4027 | int32  | 0x03 (HREG)  |      10 |
| offset15                       | 4029 | int32  | 0x03 (HREG)  |      10 |
| offset16                       | 4031 | int32  | 0x03 (HREG)  |      10 |