The tMPC-04 is a 4-input pulse counter designed for use with any meters with pulse outputs. It communicates via Modbus RTU to provide pulse counts, calculated energy and estimated power. Other measures can also be measured, e.g. flows from water or gas meters. Conversion to these units is based on user-entered coefficients (e.g. pulses per kWh), the default is 1000 pulses per unit.
Out of the box, the tMPC-04 is pre-configured with:
Modbus Slave ID: 1
Pulse Conversion Factor: 1000 pulses per unit (e.g., imp/kWh) for all 4 inputs
If these settings match your energy meters, the device is ready for immediate use. Otherwise, for setups with multiple pulse counters or different pulse conversion factors, refer to the Advanced configuration section.
The tMPC-04 integrates seamlessly with LK4 and LK3.5+ devices. It can be powered directly from the LK controller using its 5V 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 pulse counters, energy or power values.
To update the firmware, the tMPC-04 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.
You can enable bootloader mode in one of two ways:
Via USB Console
Connect the device to a PC and open the serial console (see instructions in Advanced configuration).
Then, send the command: bootloader.
The connection will be interrupted, and the device will restart in bootloader mode.
Via Hardware Button
Open the device casing to access the FLASH / SW1 button.
Press and hold this button before connecting the device to the PC via USB.
Keep holding it for a moment as the device powers on. Once it enters bootloader mode, you can release the button.
💡 Firmware files are available in the Downloads section.
To modify the settings, you will need to connect the tMPC-04 to a computer via USB. The device can be powered through USB, so no additional power connections are necessary.
To establish a connection with the pulse counter, you'll need an application that can handle serial communication. Popular choices include:
PuTTy
TeraTerm
PySerial (Python library), which includes useful tools like pyserial-miniterm (for managing connections) and pyserial-ports (for listing available COM ports).
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
Connect the Device
Plug in the tMPC-04 and run the command again. The new COM port (e.g., COM11) will represent the connected device.
Connect to tMPC-04
Use the following connection parameters:
Baud rate: 115200
Byte size: 8 bits
Parity: None
Stop bits: 1
Example command:
pyserial-miniterm COM11 115200
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).
Set the Modbus address. Parameters: X - address to set, number <1, 255>.
debounce_time? | d?
Get debounce time for pulse counters (in ms).
debounce_time=X | d=X
Set the debounce time for pulse counters. Defines the minimum pulse length, shorter ones will be ignored and not counted. Parameters: X - value in ms, number <0, 65_535>, for 0 the function is disabled.
power_estimation? | pe?
Get power estimation flag for pulse counters (0 - OFF, 1 - ON).
power_estimation=X | pe=X
Set power estimation flag for pulse counters. Defines whether the power estimation is enabled. It can be disabled if not needed or to improve the measurement range of pulse frequency from ~2 kHz to ~4 kHz (the limitation due to the pulse duration and shape remains). Parameters: X - value 0 - OFF / 1 - ON, number <0, 1>.
auto_save? | as?
Get the value of the auto-save function. This is the interval in seconds at which the counters are saved.
auto_save=X | as=X
Set the value of the auto-save function. Parameters: X - value in seconds, number <0, 65_535>, for 0 the function is disabled.
counter_cfX? | ccfX?
Get conversion factor for pulse counter. Parameters: X - counter number <1, 4>.
counter_cfX=Y | ccfX=Y
Set the conversion factor for the pulse counter: the number of pulses per unit, e.g. imp/kWh. Parameters: X - counter number <1, 4>; Y - number of pulses, number <1, 65_535>.
counterX? | cX?
Get the value of the pulse counter, i.e. the number of pulses it counted. Parameters: X - counter number <1, 4>.
counterX=Y | cX=Y
Set the pulse counter value. Parameters: X - counter number <1, 4>; Y - number of pulses, number <0, 1_073_741_823>.
read_status | rs
Read the saved status of the counters.
save_config | sc
Save configuration to Flash memory. It should be called after changing the Modbus address, counters' conversion factors, debounce time, and auto-save function to keep them after a restart.
save_status | ss
Save the status of the pulse counters to Flash memory. It should be called after changing the value of the pulse counters (the number of pulses) to keep them after a restart.
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
Turn on or off verbose mode, which displays more messages.
help | ?
Display this help message with a list of available commands.
Some commands are useful only in special cases, which I present below.
Modbus addressing: When using multiple tMPC-04s on one Modbus bus or with another device with a repeating address, it is worth using the address=X command to change it to a unique one.
Debounce time: If the device counts excess pulses, the command debounce_time=X can be used, which will cause the shorter pulses to be ignored.
Automatic saving: If it is required to keep the counters in the event of a power failure etc., the command auto_save=X should be used, resulting in their state being periodically saved to permanent memory. Be mindful of flash memory wear, as it has a limited number of writes (rated for 100k). Therefore, when using this feature you need to choose a value that is an acceptable compromise. For example, the value of 300 (seconds) should allow for about a 1 year of operation, and 1800 should allow for more than 5.5 years.
The devices use a wear-leveling file system, which should increase the expected number of writes significantly (our test device performed over 440k writes without errors so far).
Saving changes: After changing settings using the commands: address=X, debounce_time=X, power_estimation=X, auto_save=X, counter_cfX=Y, you must use save_config to save changes to permanent memory. Otherwise, they will be lost upon power loss or device restart.
The accuracy of pulse measurement depends on the frequency, pulse duration, and rise/fall times. In normal operation with power estimation, the pulse duration should be no shorter than 0.34 ms. In high-speed mode (without power estimation), the pulse duration can be as short as 0.19 ms.
For most applications, measurement errors should not exceed 0.1%. In our tests, if it was inaccurate it was 1 or 2 pulses too many or too few.
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.
Tinycontrol
