Octopus Flex PCB (SulaJalmari)

nRF52840-based flex PCB project with a shape of an octopus. Because why not. You can read the story from final.md.

Hardware specs

Board Structure: 2x Flex PCBs (acting as the octopus head and legs) and 1x FR4 PCB (acting as the base board).
MCU: nRF52840-QIAA (soldered directly to the flex PCB with a stiffener on the reverse side).
IMU: ICM-20602 accelerometer (shares an interrupt line with the light sensor).
Light Sensor: XYC-ALS21C-K1 I2C ambient light sensor (shares an interrupt with the IMU).
Leg LEDs: 8x Blue LEDs running at 2mA (LED0603-RD).
Eye LEDs: 2x Addressable RGB LEDs (WS2812B-2020).
Power & Battery: TP4054 50mA battery charger, ME6211C22M5G-N 3V3 LDO, and XC6206P362MR 3V6 LDO (dedicated to the addressable LEDs).
Connectivity: Bluetooth with a minimal PCB trace antenna, USB-C for power/programming/serial, and a 5V rail to chain multiple devices together.
Audio & Haptics: Buzzer with a driving transistor, plus a footprint for a vibration motor (motor ultimately not installed in the final version).
Interface: 2x tactile user buttons, 1x tactile reset button, and an on/off switch.
Debugging: Base board debugging pins compatible with a standard ~$3 DAPLink debugger via pyOCD/OpenOCD.
Aesthetics: Silkscreen suction cups and mouth.

Schematics and gerbers are under Hardware/V3

Because the assembled PCBs take the physical shape of an octopus, the whole device wobbles when shaken.
When the device is wobbling and the LEDs are running PWM, the movement actually allows you to see the PWM cycle with your naked eye.
The IMU is mounted in the very top of the head. This means you can tap the top of the device, and the accelerometer registers it as a physical button press.

During "stress testing" (read: repeatedly slamming it against the base board), some of the MCU pins eventually detached. Please don't torture the electronics!
The vibration motor was mostly unnoticeable, leading to its removal from the final assembly. (Pins to connect a motor still exist)
Transporting an assembled device safely is tricky.

Checkout chill project for building zephyr app with MCUboot.

Paper cutout with magnet connections.