We were choosing a front display from ready-made variants, but no such displays would meet our size, pixel density, or price criteria. Therefore, we decided to make our own matrix on a custom board. To determine the size of the display, we tried to write “Busy” in the world’s main languages and see if the word fits. For symbols, 8 pixels in height is enough, and 64 pixels in width is the minimum value to fit the word “busy” in Czech — the longest variant among all. At this stage, the front screen matrix 64x8 pixels resolution was chosen.

Here is the first test board with 2.1x2.1 mm diodes, with a 1.5 mm distance between diodes. Still, the display size, together with the body, turns out to be too big, which is handy to put the device in a bag.

Now we are considering five different types of diodes with sizes from 1 to 1.6 mm. We plan to make test matrices of 8x8 pixels with different diodes on one board to check the brightness and choose the final version. At the time of writing, these test modules are still in production.

It is expected that such a size of the diodes will increase the resolution to 80x16 pixels so that more information can fit on one screen, and the size of the matrix itself will become smaller. But so far, it is unclear how these super small RGB diodes will look in real life. Perhaps the community will suggest something. What types of small diodes would you recommend?

Block diagram

The first prototypes were made on Arduino, but in mass production, it is planned to use the ESP32-S3-WROOM1 module. This module has Bluetooth LE and Wi-Fi capabilities, can fall asleep to save energy, has many peripherals, and has a low price tag. Perhaps we will switch to something like NRF, but ESP32 does its job so far.

Stay tuned

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