RaspberryPi Wall mounted display

Overview

This project allows you to control the Sure P4 32x8 displays. Though, it is written for this specific version, it should pretty much work for all Holtek HT1632 based matrix displays.

The main goal is to give a generic, pluggable way to interface different kinds of applications with the display, without having to bother with the driver stuff.

This package also comes with an HTTP-API, making it possible to easilly interface with 3rd party stuff (e.g I'm using it for a Home Assistant integration)

Application Design

Tha main application consists of two two basic parts:

curses-client, an interactive client, probably best used to test the hardware setup and display capabilites.

fifo-client, this client will listen for API queued commands on named pipe. This queue is what you will interface with from your own application.

Both of these applications also come in a mock- version. These will work without the physical hardware, and is perfect for test setups or debugging the API usage.

Take a look at the Server API, for typical usage. A good starting point to understand how stuff works together is running ./bin/mock-fifo-client and python http-api/test.py

API

HTTP API

The HTTP API server is a simple wrapper of the fifo client, and its goal is to expose all the functionality present there as HTTP endpoints.

The server is exposed on port 8080.

Endpoint	JSON-payload	Example
/text	text: string, time: bool	{ "text": "foobar", "time": true }
/time	format: string	{ "format": "%H:%M:%S" }
/scroll	arg: string	{ "arg": "none" }
/brightness	value: 0-15	{ "value": 10 }
/clear	N/A

To call the HTTP endpoint, simply POST to the endpoint, ie:

curl -i http://localhost:8080/time -d '{"format": "%A, %b %-d %H:%M:%S"}'

FIFO Client

The API for the fifo-client is exposed through the named pipe at /tmp/raspberry-display.

All commands are on the format, command:argument, terminated by \n. Some commands do not take an argument, in this case, it will simply be omitted, e.g command:.

Currently, only a limited set of ascii characters are supported. The API expects iso-8859-1, and any unknown characters will simply be rendered as a single space.

Command	Argument	Details
text	text to display	Changes the text to render. It will not change other parameters, like scroll mode.
text-time	text to display	Shows the current time, together with a user supplied text
time	optional format	Display a dynamic time, using strftime formatting.
scroll	left	Scroll text from right to left
scroll	right	Scroll text from left to right
scroll	auto	Scroll text if it exceeds the display area
scroll	none	Disable scrolling
scroll	reset	Restart scrolling, typically useful when changing text
brightness	0-15	Set display brightness
quit	n/a	Quit client and turn off display

Building

First install the system pre-requisites and the WiringPi library.

You might want to change the display headers if you have a setup that is different than the reference setup.

If you're on a debian system, like raspbian, this is simply

./install-prereqs-debian.sh
./install-wiringPi.sh

Once this is done, you should be able to build the project with

make

Installation

Installing the application will place the binary in a system wide location, and create systemd service files to make sure the process is always running.

NB: The service will be installed as the current running user. For this to work, the user needs access to the SPI-device.

After you have built the application, you can install it with

sudo make install

This will install the fifo-client to /usr/bin/fifo-client, the http-api to /usr/local/bin/display-http-api and create systemd service files.

To (re)start the services, run

sudo systemctl restart raspberry-display-driver
sudo systemctl restart raspberry-display-server

To view log files, you can use the systemd journal

sudo journalctl -f -u raspberry-display-driver
sudo journalctl -f -u raspberry-display-server

To uninstall

sudo make uninstall

Hardware

The application is designed to use spi0 on the rasperry pi, and four generic GPIO pins. This can be changed, but for a basic setup, just follow the reference connection.

All pins referenced are physical pins. The application uses WiringPi-numbering for CS-pins. These will be different from the physical pins (use this guide for WiringPi numbering).

Pin	Usage
2	5V
6	Ground
3	CS1
5	CS2
8	CS3
10	CS4
19	MOSI/Data
23	SCLK/WR

Reference hardware

Acknowledgements

This project is written by Torkild Retvedt, as a rewrite of a similar project for the Arduino UNO

Much of the ht1632 driver is inspired by this repo.

License

This software is licensed under the MIT license, unless specified.