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A web connected LCD display module

Project description

pi_display_webthing

A web connected LCD display module

This project provides a webthing API to an I2C LCD module such as a HD44780 1602 LCD Module on the Raspberry Pi. As a webthing, the LCD can be discovered and controlled by home automation systems or custom solutions supporting the webthing API.

example display

The pi_display_webthing exposes an http webthing endpoint which supports controlling the display via http. E.g.

# webthing has been started on host 192.168.0.23

curl http://192.168.0.23:8070/properties 

{
    "text": "Hello\n\rraspi",
    "upper_layer_text": "Hello\n\rraspi",
    "upper_layer_text_ttl": -1,
    "middle_layer_text": "uploaded: 41",
    "middle_layer_text_ttl": -1,
    "lower_layer_text": "",
    "lower_layer_text_ttl": -1
}

Here, the text Hello\n\rraspi will be displayed. The text of the middle layer uploaded: 41 will be covered by the upper layer. If the text of the upper layer will be cleaned, the displayed text is uploaded: 41. By setting the ttl of the layer, the text of the layer will be disappear after expiration of the ttl. Value -1 means that ttl is deactivated.

The text of a dedicated layer can be updated as shown below

curl -v -X PUT  -d "{\"upper_layer_text\": \"Hello world\"}" http://192.168.1.101:8088/properties/upper_layer_text

The RaspberryPi/LCD hardware setup and wiring may look like HD44780 1602 LCD module. By default, Raspberry Pi OS disables I2C. Please refer Configure I2C to activate I2C and to detect the address of the LCD module.

To install pi_display_webthing you may use Docker or PIP package manager such as shown below

Docker approach

sudo docker run -p 8070:8070 --device /dev/i2c-1:/dev/i2c-1 -e i2c_expander=PCF8574 -e i2c_address=0x27  grro/pi_display_webthing:0.1.0

PIP approach

sudo pip install pi_display_webthing

After this installation you may start the webthing http endpoint inside your python code or via command line using

sudo display --command listen --port 8070 --i2c_expander PCF8574 --i2c_address 0x27

Here, the webthing API will be bind on port 8070 using a 2/16 display layout on address 0x27. Further more the port I2C port expander name has to be set. The expander name should be written on the microchip. Supported port expanders are PCF8574, MCP23008 and MCP23017

Alternatively to the listen command, you can use the register command to register and start the webthing service as systemd unit. By doing this the webthing service will be started automatically on boot. Starting the server manually using the listen command is no longer necessary.

sudo display --command register --port 8070 --i2c_expander PCF8574 --i2c_address 0x27

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