EMS Bus Interface Board Manual V0.9

User Manual:

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EMS bus interface board manual
Current board version: 0.9 - April 2018 – Last update 19 October 2018.
Please see the Github page for all the details about working with the EMS bus.
https://github.com/bbqkees/Nefit-Buderus-EMS-bus-Arduino-Domoticz
This instruction is for both version V0.8 and V0.9 boards. The only difference is the silkscreen (so the
text on the board).

Connectors on the board

1

2

4
3
Number
1
2

J#
J1
J2

Header function
EMS screw terminal
Controller header

3
4

J3
J4

EMS service jack plug
RX resistor selector jumper

5

J5

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 (5V) or 100E (3.3V)
resistor.
Left pin EMS 8-16V. right pin GND. Max
power draw 200mA cont.

Due to improvements made after the production of the V0.8 PCB please note the following:
The board can now be powered with either 5V or 3.3V. However, this is now 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. Although the text on the V0.8 boards might suggest
otherwise, the yellow jumper setting J4 is not a voltage selector but an RX resistor selector. This
change was made to get an improved handling when using an ESP8266.
Furthermore R15 is no longer populated for the same reason, this is intentional.
Although indeed the board has now also been fully tested with the ESP8266 in both read and
write mode, do not ask me for the code at this moment. I do not provide ANY support for the
ESP8266/ESP32. See links on my Github to ES8266 code.

Connecting to the controller
Although header J2 on the V0.8 boards says 5V, you can power the board with 5V or 3.3V. 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 very quickly due to the voltage difference. Furthermore you need to add a big capacitor at
the input of the buck to compensate for voltage drops on the bus.
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
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Author                          : Kees Roos
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Create Date                     : 2018:10:19 11:11:09+02:00
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