Bitmap to Byte array for e-ink display

Over the past few months, Andrew has been working on a new circuit for a custom home alarm system to replace our current hardwired commercial alarm.

For the display panel on the new alarm, we are going to be using an e-ink display to show the status of the alarm and the sensor status for each door and window.

We sourced a basic 2.9-inch e-ink display from eBay and it is a 296x128 pixel back and white display and an SPI interface from https://www.waveshare.com/wiki/2.9inch_e-Paper_Module

The display uses an array of bytes to write to the display panel with each byte controlling 8 pixels. You can either write the entire display each time or select a starting x and y location and write the data as required.

The manufacturer has a windows application to convert images into the data format required but it is all in Chinese and we couldn’t get it to work.

I wrote a simple Windows form application which opens a bitmap file and then loops through each row and column and gets the hex value for each pixel. If the pixel is black it then returns “0” for a black pixel or “1” for a white pixel.

Each row is then combined into a series of 1’s and 0’s and converted into a byte array which is then saved into a StringBuilder and formatted as HEX values with comma separators.

The resulting text output can then be saved into a text file and used on the panel's control software to write to the display via the SPI bus.

Converting the above 16px x 16px image results in the following code with each row of pixels being converted into two-byte values per line.

{
0x9C,0xE7,
0x08,0x43,
0x08,0x43,
0x9C,0xE7,
0xFF,0xFF,
0xCF,0x39,
0x86,0x10,
0x86,0x10,
0xCF,0x39,
0xFF,0xFF,
0xF9,0xFF,
0xF0,0xE7,
0xF0,0xC3,
0xF9,0xC3,
0xFF,0xE7,
0xFF,0xFF,
};

The image below shows a converted photo of me into a 1-bit BMP file and then converted into the byte array for the display.

The source code for the app can be downloaded from https://github.com/briandorey/BitmapToByteArrayConverter