Khartoum

Experimenting with Waveshare ePaper for the Raspberry Pi

Writing code in Kotlin Native to control and display images and text on a Waveshare ePaper HAT for the Raspbery Pi.

It is not possible to build this application on a Raspberry Pi, as Jetbrains do not support the Raspberry as a build platform (despite it having the same core architecture as the M-series ARM processors used on Macs).

Makes use of the bcm2835 C library for hardware control. It recreates some of the Waveshare GUI C example functions, in Kotlin, in a library I am calling Khartoum. So far, the following functions are available:

The Khartoum binary must be run as root (sudo -E ./Khartoum.kexe) on the Raspberry Pi.

Libraries used

• Kotlinx serialization
• Kotlinx datetime
• Native c-libraries:
  • libCurl
  • bcm2835 C library

Links and references

Spotify

Requires two environment variables to be set:

• SPOTIFY_CLIENT
• SPOTIFY_SECRET
• SPOTIFY_REFRESH_TOKEN

To create a client ID, register a new application through the developer dashboard. You'll also find the secret here.

To authorize the application, I should be requesting the authorization through the code flow mechanism. But this application runs headless and in the background. Instead, I need to get a code from:

https://accounts.spotify.com/authorize?response_type=code&client_id=<<CLIENT_ID>>&scope=user-read-currently-playing&redirect_uri=https://www.liamjd.org/spotCallback

Which redirects to https://www.liamjd.org/spotCallback?code=<<CODE>>

And from that code, I can request a refresh token from the URL:

curl -d client_id=<<CLIENT>> -d client_secret=<<SECRET>> -d grant_type=authorization_code -d code=<<CODE>> -d redirect_uri=https%3A%2F%2Fwww.liamjd.org%2FspotCallback https://accounts.spotify.com/api/token

That refresh token can then be used to request a new access token and is stored as an environment variable.

Need the -E option to be passed to sudo for them to be available. Run the command with nohup to ensure it keeps running even after logging out (sudo -E nohup ./Khartoum.kexe &).