Description

eink-server is a framework for displaying content on an Inkplate e-ink display. The Inkplate device connects to a server over Wi-Fi. Using Python 3 code, the server computes the content to display and then sends it to the e-ink device in the form of an image. The display periodically queries the server for updated content.

This approach has pros and cons, compared to doing all of the work on the Inkplate device:

Pros:

• The content is computed on a more powerful device, which has much more memory, a faster CPU, non-volatile memory, etc.
• Code changes can be made remotely, without connecting the Inkplate to a PC and uploading new software.
• Code changes can be tested locally, without waiting a couple of minutes for the new software to be compiled and uploaded to the e-ink device. This makes the development process faster.
• Programming the content is arguably easier, because it is in Python, which is a higher-level language than C++.

Cons:

• Some setup is required.
• A server PC must be up and running in order to make content updates.
• We cannot respond to touchpad or other Inkplate inputs.
• Displaying a clock is problematic.
• Some flexibility is sacrificed.

A server is implemented by subclassing the Server class. The base class declares a render() method, which is overridden to return an image indicating the content to display. Images are represented as Pillow library Image objects. Servers also have methods indicating how often the content should be updated. This informs the Inkplate device how often to query the server.

Getting started

You can use the skeleton code generator to autogenerate your own Flask server:

• Make sure you have the Arduino IDE, Python 3, and pip installed. You can use venv if you want, in which case you will have to make adjustments to the below instructions.

  python3 --version
  pip3 --version

• Set up the Arduino IDE to work with the Inkplate device: https://e-radionica.com/en/blog/add-inkplate-6-to-arduino-ide/.

• Obtain a fixed IP address or domain name for your PC. There are three options:

  • (recommended) Assign your computer a static local IP address (such as 192.168.1.70), using your Wi-Fi modem/router's settings. If you do this, then your e-ink device will need to connect to the same Wi-Fi network as your PC.
  • Obtain a domain name for your computer, and forward web requests to your computer using port forwarding, through your Wi-Fi modem/router's settings. You can get a free domain name using a service such as No-IP.
  • Obtain a static global IP address for your computer, and forward web requests to your computer using port forwarding, through your Wi-Fi modem/router's settings. Often, this is not possible, because it depends on your Internet service provider.

  The instructions for configuring your modem/router will depend on what model you have. If you look at your modem/router device, it should tell you a URL you can visit to configure it, such as http://192.168.1.255. Open this URL in your web browser and navigate around until you see the appropriate setting.

  Note: If you make your server available through a public domain or IP address (the second and third options), then anyone will be able to access it. This is because the eink-server library does not do any authentication.

• Set up the eink-server library:

  git clone https://github.com/btrekkie/eink-server.git
  cd eink-server
  pip3 install .

• Run the skeleton code generator, and follow the on-screen instructions. When prompted for the server URL, use the IP address or domain you assigned to your PC in a previous step.

  einkserver skeleton

• Install the server's dependencies:

  cd ~/eink_server
  pip3 install -r requirements.txt

• Run the Flask server. (If you entered in a port number other than 5000 when asked for the URL, you will need to specify the port number using the -p argument.)

  cd ~/eink_server
  flask run --host=0.0.0.0

• In another console, using the connect command, make sure you can connect to the server using the URL you supplied to the skeleton code generator:

  einkserver connect [URL of e-ink server]

  If the connection is successful, you should see a window with the default content. If the connection fails, the console will print an error. In that case, check the configuration of your modem/router, and make sure your Flask server is running.

• Run the Arduino IDE. Go to File -> Open.... Navigate to the client code directory you supplied to the skeleton code generator. Open the INO file in this directory.

• Connect your Inkplate device to your computer using a USB cable. Switch your e-ink display on.

• In the Arduino IDE, click the upload button (or go to Sketch -> Upload). If successful, the e-ink display should show the word "Connecting" briefly (or just a wi-fi icon), followed by the default content.

Once you've set up your server, take a look at the Python code it generated. Now you should modify it to suit your needs. (You do not need to read or modify the client code.)

Examples

• wikipedia: Displays the Wikipedia homepage. This can easily be modified to show another webpage. It requires the google-chrome command to be present in the path.
• weather: Displays a five-day weather forecast, using the OpenWeatherMap API.
• slideshow: Displays a slideshow of all of the images in a given directory.

Documentation

See https://btrekkie.github.io/eink-server/index.html for API documentation.

Possible future enhancements

These are ways that eink-server could be improved in the future:

• More transport mechanisms. For example, we could add support for Bluetooth and serial connections.
• Security. Perhaps it would be sufficient to encrypt the request and response payloads using AES with a randomly generated key. (My initial thought was to use HTTPS and basic authentication. But for some reason, if I try to stream an HTTPS response using WiFiClientSecure.read, and the response is larger than around 4 KB, then the attempt fails with a return value of -1.)

Credits

• Icons made by fjstudio and Smartline from www.flaticon.com
• The Gentium Plus font is licensed under the SIL Open Font License.