Octopus Flex PCB (SulaJalmari)

An nRF52840-based flex PCB project with a shape of an octopus.

Hardware Specifications

This section covers the exact specifications of the third (and final) prototype:

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.

Wobble Physics: Because the assembled PCBs take the physical shape of an octopus, the whole device wobbles when shaken.
Visible PWM: 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.
Tap-to-Click: 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.

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

Checkout chill project for building zephyr app with MCUboot.