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
Fun facts
Fun Things
- 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.
Flaws
- 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.
Software
Checkout chill project for building zephyr app with MCUboot.
History
Idea
Paper cutout with magnet connections.
First prototype
Second prototype
Final version
