General information

After going through several prototypes and lots of testing I can now offer the EMS Bus Gateway; a complete plug and play set which includes the EMS bus interface circuit, an on-board power supply and on-board Wemos D1 Mini type ESP8266. All modular by design and neatly packed in a small enclosure (90x50x24mm). Just plug in the device to the service jack on the boiler with the supplied jack cable and stick it to the side of the boiler (its magnetic). No additional cables are needed and everything is powered from the service jack itself.

This new design has the same EMS bus interface circuit as the previous 'EMS interface board V0.9' which is used succesfully by many people all over Europe. It is now combined with the Wemos D1 Mini and a buck power converter on the same PCB.

Furthermore it has a connector for directly connecting DS18B20 sensors, and more of the Wemos I/O pins of the Wemos are accessible as well for all your custom tinkering.
Although the new board is intented to be plugged into the service jack, it can still be connected to the EMS bus via the thermostat wires instead. But you need to power the board via usb in that case.

Proddy firmware logoThe Wemos comes preloaded with stable firmware from the great Proddy's Github repository so you have a working setup using MQTT.
On first boot the Wemos will create an access point on which you can login with Telnet and make the appropriate settings for your own network. So for this kit you don't need any soldering or real programming skills. You do however need to properly configure your home automation system.

EMS Bus Gateway on boiler
EMS Bus Gateway on boiler
EMS Bus Gateway kit
EMS Bus Gateway full kit
EMS Bus Gateway internals
EMS Bus Gateway internals

Compatibility

Boiler compatibility

The interface is electrically compatible with all Bosch brand boilers, heat pumps and devices that have an EMS, EMS+, EMS2, EMS Plus, Heatronic or Heatronic 3 interface. Sometimes the bus is also named f.i. 2-wire bus.
Bosch brand boilers include f.i. Bosch, Buderus, Nefit, Junkers and Worcester.
I cannot guarantee that the interface will work with your specific boiler. Check before purchasing whether your boiler has an EMS compatible bus.

EMS bus device (thermostat) compatibility

Support for thermostats and other EMS bus device like solar mixer modules is firmware dependant.
Please consult Proddy's Github repository for the list. New devices are added all the time.

What can you use it for?


Home automation system integration

You can connect the Gateway with your home automation system like Home Assistant or Domoticz so you can read out all the boiler parameters and control f.i. the thermostat.
You can log all boiler data and make nice plots with f.i. Grafana.

Full external boiler control and central heating tuning

With the Gateway you have full control over the boiler and the thermostat, it is possible to f.i.:

  • Monitor your airbnb's use of hot water and heating remotely.
  • Limit shower times and override maximum heating temperature in your own house, student apartments, B&B or second house.
  • Log and tune parameters of the boiler to save on energy.

Connecting to the boiler

Main method - service jack

With the supplied jack cable you can plug in the gateway to the service jack of the boiler. This is usually located on the front.
Then stick the gateway to the metal side of the boiler. The underside of the case is magnetic.
The entire device including the Wemos is powered via this service jack. So no additional power supply needed. Just the jack cable is all you need.

Alternative method - EMS/thermostat wires

If your boiler does not have a service jack or it does but you want to mount the EMS Bus Gateway elsewhere you can use the screw connector to connect to the two EMS bus wires. This can be in parallel with the thermostat or from inside the boiler.
In this case you need to power the device by plugging in a USB power supply directly to the Wemos.

Do not connect both the jack and the EMS wires via the screw terminal at the same time!

Modular design

To provide maximal flexibility and serviceability both the buck power converter and the Wemos are mounted on a header so they can be easily removed or exchanged in case of failure or upgrade.

EMS ESP kit
EMS Bus Gateway full kit with opened case
EMS ESP kit main components
EMS Bus Gateway main components

Wemos D1 mini connector

On the right side of the board you can find the header used for Wemos D1 Mini like boards. Included is a Wemos D1 Mini V2 type ESP8266. You can use other pin-compatible Wemos or ESP8266 devices if needed like the Wemos D1 Mini V3 or the Wemos D1 Mini Pro.

Buck power converter

In the middle of the board connector J13 is the header for a buck power converter. If you buy a complete kit a suitable stress tested buck is already installed.
This buck will step down the 8 to 12 Volts on the service jack to 5 Volt as the source for the Wemos board. The internal voltage regulator of the Wemos will then deliver 3.3V for the entire board.

Because almost all buck converters have the same pinout you can exchange the existing buck for another one.
The board has f.i. also been tested with several Polulu bucks.
The pinout of the header is 5V output, GND, VIN from the jack and the most right pin is not connected. So if you have a standard 3 or 4 pin buck it will fit.

Board headers

EMS ESP kit headers

Connecting external DS18B20 sensors

On the right side of the board below the Wemos you can find a 3-pin 2.5mm pitch JST XH connector.
If you purchased a complete kit a JST cable is included. If you need to source this cable yourself then look for RC car battery cables. These are usally the same ones.
When seen from the front the left pin is GND, the middle pin goes to D5 of the Wemos and the right pin is 3V3. A 4k7 pull up resistor is already on the board.
If however this value is not sufficient, you can add a through hole resistor on position R20 (also below the Wemos). This optional through hole resistor is routed in parallel to the 4k7 resistor.
You can solder one or more DS18B20 sensors to the JST cable or use f.i. a screw terminal.

Additional non-populated internal connectors

Headers J15 and J16

J15 is a single pin connected to GND and J16 is connected to 5V and GND.
These pins can be used to add f.i. a 19mm supercap.

Headers J20 and J18

J20 is a single pin connected to 3V3 and the adjacent connector J18 is connected to GND, Wemos TX, Wemos RX, Wemos D2 and Wemos D3.

Header J19

J19 is a three pin connected to GND, Wemos D0 and Wemos A0.

On board LED footprints

Below the Wemos there is an additional parallel footprint for either a 0805 SMD or a 3mm throughhole LED. One side is connected to GND.
These footprints are both connected in series with the same resistor R18 to pin D1 of the Wemos so you can use either the SMD or the through hole footprint.

Firmware and configuration

Proddy firmware logoThe Wemos comes preloaded with stable firmware from the great Proddy's Github repository so you have a working setup using MQTT.
On first boot the Wemos will create an access point on which you can login with Telnet and make the appropriate settings for your own network. So for this kit you don't need any soldering or real programming skills. You do however need to properly configure your home automation system.

Configuration for Home Assistant

Home Assistant logo MQTT communication in the firmware is preconfigured for Home Assistant. Please follow the instruction in the repository to integrate the EMS ESP interface to Home Assistant.

Configuration for Domoticz

domoticz logo For Domoticz you need to use NodeRed see f.i. this topic and as an alternative a beta plugin is also available.
The plugin will be expanded soon with new sensors etc.


Firmware support

The firmware is not my own but a very frequently updated open source project maintained by others. Because I can't keep up with all the intricate details of the code, support by me is limited to general questions. For all technical questions and issues please refer to the repository itself.

Ordering information and availability

You can buy several versions of the EMS Bus Gateway on the ordering page here.
Availability of the new design is spotty at the moment as I need to soure more components from different suppliers and assemble by hand and test everything.