ESP8266 based MQTT adapter for Max7219 based LED display.

Subscribes to /leddisp1/show and displays messages on my Max7219 based display.

ESP communicates to an arduino through SPI. String messages of the form "N,M," are parsed where

• N is the timeout in seconds after which the arduino clears the display.
• M is the mode, currently supports
  • 0 for stationary display
  • 1 for scrolling display

The same string is expected as the payload for the topic over MQTT. ESP sends only 32 bytes of the payload to the display.

Wiring

Arduino should be in 'slave' SPI mode. Appropriate level conversion should be used for 5V arduino. Almost all of data flows from ESP to the arduino.

ESP             |  Arduino
----------------+---------
GPIO4           |  10 (SS)
GPIO13 (SPID)   |  11 (MOSI)
GPIO14 (SPICLK) |  13 (CLK)

The GPIO4 and GPIO5 might be inverted on some ESP modules (it was for my ESP-12). My configuration works with arduino running the sketch in aniline/arduino-sketchbook/mqtt_display.

Building

Setup the variables as required by https://github.com/esp8266/source-code-examples . This includes stuff like:

XTENSA_TOOLS_ROOT=/opt/Espressif/crosstool-NG/builds/xtensa-lx106-elf/bin
SDK_BASE=/opt/Espressif/ESP8266_SDK
FW_TOOL=${XTENSA_TOOLS_ROOT}/esptool
ESPTOOL=${XTENSA_TOOLS_ROOT}/esptool.py
ESPPORT=/dev/ttyUSB0

Build checkdirs because the Makefile symlinks some .c files from SDK in the first step.

$ make checkdirs
$ make

Flash using. Pass ESPPORT=<ESP serial port> if it changed from the time you set the environment.

$ make flash

Configuring

It uses the tuanpmt's library and configuration mechanism. It loads the settings in user_config.h to flash if the magic number CFG_HOLDER is different from whats in the flash. So when you update configuration change CFG_HOLDER to re-save the values to flash.

Thanks

• tuanpmt's MQTT Library: esp_mqtt