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esonhon / goepd

Epaper driver for EPD displays

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GOEPD

A golang spi driver for Waveshare's epd displays using periph.io under the hood.

Before you dive in

This is essentially in alpha at the moment, and as such is liable to change a bit at short notice ( although a goal is to keep the api simple ).

In addition, the only currently supported configuration is a 4.2b module ( 4.2inches in black white and red. More coming soon...)

I'm hoping, though haven't explored it yet, that all the displays, 4.2 inches and under at least, share a common command api. If not, support for other devices may take a bit longer.

update

CLI tools are now prefixed with epd rather than goepd so they're:

  • epd-show
  • epd-serve

There's also a new one called epd-render to test out the renderer... But nothing major yet.

Tagging this with a version now and will try and keep these api's reasonably stable, especially for the cli apps.

Also, new dev will now be on feature branches and not master.

Setting up

So, we're going to assume you're connecting the display to a raspberry pi or other maker like board. You'll need to ensure its supported in periphs hosts if its not, I know there's a way to create pin mapping and host support ( I've done it before, I just can't remember how right now.)

Waveshares hookup docs are useful, I'll describe an example setup here

An example pin connection might be as follows for a raspberry pi, using pins collocated on the GPIO header ( layout here )

(Not sure if using the HAT version of an epd display differs buch. Certainly not sure if you're using a raw module).)

EPD pin RPI Pin Name RPI Physical pin Description
VCC 3.3V 17 Using 17 as its next to default SPI pins
GND GND 20 Again, closest GND to SPI pins
DIN SPI0 MOSI 19
CLK SPI0 CLK 23
CS SPI0 CE0 24 Default RPI chip select for SPI0
DC GPIO25 (also called BCM25) 22 GPIO output for Data command control. Used to tell the display when data's coming
RST GPIO24 (also called BCM24) 18 GPIO output for Reset control. Used to tell the board to reset
BUSY GPIO23 (also called BCM23) 16 GPIO input for busy status. Display will pull this low when its busy

Your choice of pins may vary, but make sure you

  • use 3.3V
  • connect the correct spi pins
  • use addressable gpio pins for the others

Get it

go get github.com/woosteln/goepd
go get github.com/woosteln/goepd/cmd/...

Use it

The main package is a library but the cmd/... bit above will have installed a couple of utilities.

epd-show

Cmd line tool to update the display.

epd-show --dc 25 --rst 24 --busy 23 https://loremflickr.com/400/300

if you want to clear the display

epd-show --dc 25 --rst 24 --busy 23 clear

(Unless using a strange configuration, at least on rpi, spi will use "" address to get first available bus)

If you're looking for something to use rather than building a go app, we've got you covered.

epd-serve

goepd-serve will start an http server that will let you post content updates to the display.

epd-serve --dc 25 --rst 24 --busy 23 https://loremflickr.com/400/300

and you can then post an update to it

curl -F 'imageurl=https://loremflickr.com/400/300' $DEVICE_ADDRESS:8080/display/content

or if you want to add some text

curl -F title=Hello \
  -F body=world \
  -F "footer=Drop's mic" \
  -F 'imageurl=https://loremflickr.com/400/300' $DEVICE_ADDRESS:8080/display/content

or post an actual image

curl -F 'imageurl=@/absolute/path/to/image.jpg' $DEVICE_ADDRESS:8080/display/content

You can post data as json or multi-part for ( necessary if you're posting and actual image).

Fields are:

  • title: String. Title text. Placed top left
  • body: String. Body text. Comes under title on the left
  • footer: String. Footer text. Placed bottom left
  • imageurl: String. HTTP url of a jpg, png or gif image
  • image: Bytes: Actual image data. jpg, png or gif

!IMPORTANT! Don't just copy and paste, remember to substitute your device address and the pins you've set up.

Library

Want to drive the display from your app, have a look at the src of cmd/goepd-show/main.go

In essence:

import (
  "github.com/woosteln/goepd"
)

var (
  SPI_ADDRESS = "0:0"
  DC = "25"
  RST = "24"
  BUSY = "23"
)

func main(){

  display, err := goepd.NewEPD42( goepd.Landscape, SPI_ADDRESS, DC, RST, BUSY )
  
  if err != nil {
    panic(err)
  }

  defer display.Close()

  content := goepd.Content{
    Title: "Example",
    Body: "Hello world",
    Footer: "Thank you and good night"
  }

  display.Show(content)

}

The renderer will try and layout content in an appropriate manner. But its pretty basic.

If you give it an image and no text, the image will be scaled to fill the display.

If you provide it text and an image, they will be laid out side by side in portrait mode and top and bottom in landscape mode. Image will be scaled to fit its allocated area.

If you provide no image, the text will fill the space.

So, if you make a better renderer to layout text and the like, you can just send it an already scaled image, but you might want to tell it not to dither it.

The internal driver will convert any predominantly red hues to red and anything else will be thresholded based on its grayscale int value. >180 = white, <180 = black.

References and libraries used

TODO List

  • Improve layout / coloring in renderer
  • Explore a better way of embedding default fonts (golangs don't work well on this display). Packages size can be quite big.
  • Verify support and create constructors for other boards
  • Include support for black/white only boards
  • Explore supporting larger display modules
  • Introduce testing
  • Verify / introduce support for HATs / raw

Contributing

If you find this useful, shout me. If you've got a PR expanding support would love to hear about it.

I may not be the fastest to integrate changes as this is only a side-project.

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Epaper driver for EPD displays

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