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 the RX resistor selector. This
addition 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.
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!!!!!!!!!
