BouLed will be inside a plexiglas sphere, so there will be no button. The two ways of interacting with it are its orientation and a WiFi remote control, which I made with an ESP32 DevKit. It opens a access point and runs an HTTP server. You connect to it with your phone (or whichever WiFi-enabled device you like), select some parameters on a web page, and send them to the ESP32. Which in turn sends them to our main board via SPI. Naturally, there’s no noticeable latency.

However, I noticed something strange. The card doesn’t automatically boot in flash when powered on, while it should (according to Espressif) when GPIO0 is not grounded. I tried connecting it to Vcc instead of letting it floating, and it boots in flash. Same behaviour on other kevkits. Except for the brand new one soldered on our main PCB, fortunately.

## Clever mistake

When Matthias was working with the simulation, he noticed the faces weren’t ordered correctly. The top 5 faces of the icosahedron, enumerated in clockwise order, would haves indices 0 1 2 4 3 in the array of matrices giving their position, instead of 0 1 2 3 4. Yet I could do all the pretty map projections without any issue, as my implementation didn’t rely on a particular ordering of the matrices. Here’s a pseudo-code version of the function that would compute these matrices :

`mat4 face = some_correct_somputation(); mat4 rotation = some_rotation(2*pi/5);  faces.add(face);  for (int i = 0; i < 4; i++) {   faces.add(rotation * face);    rotation = rotation * rotation; } `

The purpose of this was to place one face, rotate it by 2*pi/5 around the correct axis and use this as the second face. Rotate the 2nd face by 2*pi/5 to get the 3rd one, etc… This is obviously not the behaviour of this code, as the rotation matrix is squared each time, instead of being rotated by 2*pi/5. But this actually computes the right matrices! Basic group theory in Z/5Z you’d say. Funny bug I say.

## Finishing the firmware

For the different features of bouLED, we worked on different devboard, because we can’t all work on our only STM32H7 devboard. Git merge after git merge, we’re done making it all work on the same board.

## Finishing the hardware

We soldered the LEDs on the triangular PCBs last week. That was not too painful thanks to our teachers and a pick and place machine.

We’ll now start mounting the whole thing.