EMS Bus Interface Board Manual V0.9
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Wemos connections The Wemos D1 Mini versions all have the same pinout, however the text on the board may vary slightly. Below two examples. Wemos D1 Mini V3 Wemos D1 Mini V2 RX RX TX TX VC VC GD Pin EMS board VC TX RX GD Wemos pin 3V3 (NOT 5V!!) D8 D7 G or GND GD EMS bus interface board manual Current board version: 0.9 - April 2018 – Last update 14 January 2019. Please see the Github repository for all the details about working with the EMS bus. https://github.com/bbqkees/Nefit-Buderus-EMS-bus-Arduino-Domoticz Connectors on the board 1 2 4 3 Number 1 2 J# J1 J2 Header function EMS screw terminal Controller header 3 4 5 J3 J4 J5 EMS service jack plug RX resistor selector jumper 8-12-16V pin from EMS service jack 5 Remark Polarity does not matter. VCC/TX/RX/GND. Input 5V or 3.3V from controller. Only connect either J1 or J3. Select either 4k7 or 100E resistor. Left pin EMS 8-16V. right pin GND. Max power draw 200mA cont. Before shipment, this board has been fully tested on my own boiler with an Arduino in RX and TX mode on both 3.3V and 5V, and with both resistor settings. So the board you received works as intended. Keep this in mind when you created something with this board and it does not work. Do not immediately assume the board is faulty. The most likely problems are in your own code or in the connections to the microcontroller board. First try my Github examples to verify the board is working in your setup and everything is wired up correctly. If you have a persistent problem with the board you can always send an email to bbqkees+pcb@gmail.com In any case do not open a Paypal dispute. Important note: The board can be powered with either 5V or 3.3V. However, this is also the voltage for the signal level on the UART. If you use 5V to power the board, 5V will also be your UART signal level and this will potentially destroy f.i. an ESP8266. So if you are using an Arduino, power the board with 5V and if you are using a Pi or an ESP chip ONLY USE 3.3V to power the board. The yellow jumper setting J4 is an RX resistor selector. This change was made in the last board revision to get an improved handling when using an ESP8266. Furthermore R15 is no longer populated for the same reason, this is intentional. The boards’ design has also been fully tested with the ESP8266 in both read and write mode. See links on my Github to external ESP8266 code. (Like https://github.com/proddy/EMS-ESPBoiler) Connecting to the controller The controller needs to power the interface board. Connect GND as well. Do not supply the interface board with more than 5V. You can connect this board to any 5V or 3.3V compatible UART. This might be on an Arduino, ESP8266 or f.i. a Raspberry Pi. Connect the header J2 to the controller. Keep in mind the remarks in the red box above. Use the jumper of J4 to select the correct RX UART resistor setting. For most Arduino’s and the Pi this is setting 1. This setting provides a standard 4k7 Ohm resistor on the output. For the ESP8266 use setting 2. Setting 2 provides a 100 Ohm resistor on the output, specifically intended for the ESP8266 and other similar chips. If one particular setting does not work, try the other setting too. Connect RX to the RX UART serial port and TX to the TX UART serial port of your controller. If you do not need TX you can just leave the pin unconnected. On the Arduino Mega 2560 in combination with the Github sketch connect RX to RX1 (pin 19) and TX to TX1 (pin 18). If you use an Arduino UNO you have no choice other than RX on pin 0 and TX on pin 1. In case you use the UNO do not connect the EMS board to the Arduino while you are programming the Arduino, because the same serial pins are used for programming the Arduino. On the Raspberry Pi connect RX to GPIO 15 (pin 10) and TX to GPIO 14 (pin 8). Important: The interface board also puts out the 8-16V pin of the EMS service jack via header 5. This can be used to power small electronics. The interface board has 2 polyfuses that are rated for a continuous current of 200mA and they trip at 400mA. If you do draw power from the EMS service jack make sure the 3.5mm jack cable you use can handle the current as most of these cables are meant for audio and therefore have very thin wires inside. The best method to power external circuits from these pins is to use a buck converter. LDO's will overheat pretty quickly due to the voltage difference. Also take care you do not short circuit the board in any way or feed this board with incorrect voltages as this may damage the board or the EMS bus. Also make sure the wires you connect the board to are in fact EMS bus wires and NOT 24V or mains power lines!!!!!!!!! Connecting to the bus You can use EITHER the EMS bus service jack OR the screw terminal. Do not connect them at the same time, because you might short circuit the bus. If you use the screw terminal, polarity does not matter because the circuit corrects both orientations. OR Below some code examples to get you started: Arduino: https://github.com/bbqkees/Nefit-Buderus-EMS-bus-Arduino-Domoticz https://github.com/danimaciasperea/Calduino ESP8266: https://github.com/proddy/EMS-ESP-Boiler (Keep in mind this code uses the alternative RX and TX pins on the Wemos!)
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