MQTT bridge for TM1638

This is an MQTT bridge for TM1638 that runs on Raspberry Pi.

A TM1638 board usually presents a row of 8 leds, a row of 8 buttons, and a row of 8 7-segments digits display.

The purpose of this bridge is to:

• turn MQTT messages into Leds/Display actions: listen to MQTT topics and display text on the display, or power on/off the leds according to the messages received
• turn Buttons events into MQTT messages: it will publish messages on an MQTT topic when the buttons are pressed.

Example:

• You can read the button topic via Node-Red and toggle a smartplug or a smartbulb.

How to build

Build dependencies

To build tm1638-mqtt we first need to build 3 libraries:

• libbcm2835.so
• libtm1638.so
• paho-mqtt3c

Build libbcm2835.so

• Download bcm2835-1.52.tar.gz (from http://www.airspayce.com/mikem/bcm2835/)
• Untar in /home/pi. Go to /home/pi/bcm2835-1.52/, and run ./configure, then make.
• Then, go to /home/pi/bcm2835-1.52/src, and run:

gcc -DHAVE_CONFIG_H -I. -I.. -g -O2 -MT bcm2835.o -MD -MP -MF .deps/bcm2835.Tpo -o libbcm2835.so bcm2835.c -fPIC -shared

This will create the libbcm2835.so shared library. Copy it to /usr/local/lib.

Build libtm1638.so

You will find the TM1638 library source code and some building instructions on Martin’s Atelier.

$ cd
$ wget https://github.com/downloads/mjoldfield/pi-tm1638/pi-tm1638-1.0.tar.gz
$ tar xzvf pi-tm1638-1.0.tar.gz
$ cd pi-tm1638-1.0
$ ./configure
$ make

Then build the libtm1638.so shared library and copy it to /usr/local/lib:

$ cd src
$ gcc -std=c99 -o libtm1638.so tm1638.c -fPIC -shared -lbcm2835
$ sudo cp libtm1638.so /usr/local/lib/

Build libpaho-mqtt3c.so

Clone the Eclipse Paho MQTT C client repository and build it as per the instructions in its README. This will build and install the library.

Build the TM1638-MQTT bridge

• Clone this repository

• Edit the GPIO PINs to which you have connected your TM1638 to the Raspbery Pi.

In my case this is how I have connected the TM1638 to the Pi as shown below:

TM1638	RPi
STB	GPIO17
CLK	GPIO27
DIO	GPIO22

You can locate the PIN numbers in the code by looking searching for tm1638_alloc. The line reads:

   t = tm1638_alloc(17, 27, 22);

If you connect the TM1638 to different pins, edit that line.

• If needed, edit the constants at the beggining of tm1638mqtt.c:

Constant	Default value	Description
ADDRESS	127.0.0.1:1883	The IP:port of the MQTT broker
CLIENTID	TM1638ClientSub	ClientId of this client
TOPIC_LEDS	8leds	Messages received on this topic indicate the leds to light up
TOPIC_TEXT	7segs	Messages received on this topic will be written on the eight 7-segments display
TOPIC_BTTN	buttons	A message will be written in this topic when a new button is pressed.

• Run make

How to use

$ nohup tm1638mqtt &

tm1638mqtt will connect to the MQTT broker (defined in ADDRESS) and suscribe to the two topics defined in TOPIC_LEDS and TOPIC_TEXT. It will also publish messages to TOPIC_BTTN.

Topic	Format	Comments
TOPIC_LEDS	0-255 integer	The 8 bits will indicate which leds should be lighten up
TOPIC_TEXT	plain text	Text will be shown on display
TOPIC_BTTN	0-7 digit	The digit indicates the corresponding button has been pressed

Possible enhancements

• The logic can easily be modified to indicate which combination of buttons is pressed for example (when pressing multiple buttons simultaneously) or when a button is released...
• Pass the constants as options/parameters to the process via the shell, instead of hardcoded (topics, PINs)
• Code can be modified if you need a different MQTT topics hierachy/structure