EMS Interface board


EMS to TTL level interface board for 3.3V and 5V compatible UART of f.i. Arduino, Wemos, Raspberry Pi.

This product has been replaced by the new version: see it HERE.

Out of stock

SKU: ems-comp-1 Categories: ,


This is the original EMS bus to microcontroller UART interface board (previously called the ‘EMS level shifter V0.9’).
With this board you can safely connect a UART/serial port of your microcontroller or development board to the EMS bus.

Because the EMS bus is about 16VDC, works with an offset and the signal in the top few volts, the RX signal needs to be stepped down to 0-3.3V or 5V.
TX works in the current domain so this board converts the TX signalling of the UART into a specific current signal for the EMS bus.

Did not understand anything what you just read? That’s OK because the main reason I built this board is so you don’t have to worry at all about the electrical part of the EMS interface. Just plug it into your favorite microcontroller and off you go.

The board is 3.3V and 5V UART compatible and works with all EMS, EMS+, EMS2 and Heatronic 3 and 4 boilers.
This board is compatible with f.i. every Arduino, Atmel, ESP8266, ESP32, Wemos, NodeMCU, Raspberry Pi and other microcontrollers.
For more information have a look at the product wiki.

You can connect the board to the bus via the 3,5mm service jack or via the EMS/thermostat wires on the screw connector.

If you are buying this board because you want to use it on a iRT boiler please purchase the iRT modified item.

Each interface board is completely assembled and tested on an EMS boiler before shipment.
Currently the color of the circuit board is blue. There is no difference with the white circuit board as in the images.

Additional information

Weight 0.06 kg
Bus compatibility

EMS, EMS Plus, EMS+, EMS2, Heatronic


3,5mm Service jack, EMS bus wire screw terminal, EMS power out header