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2.7 KiB
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59 lines
2.7 KiB
Markdown
# Octopus Flex PCB (SulaJalmari)
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An nRF52840-based flex PCB project with a shape of an octopus.
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<img src="pics/device_diagram.png" height=800>
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## Hardware Specifications
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This section covers the exact specifications of the third (and final) prototype:
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* **Board Structure:** 2x Flex PCBs (acting as the octopus head and legs) and 1x FR4 PCB (acting as the base board).
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* **MCU:** nRF52840-QIAA (soldered directly to the flex PCB with a stiffener on the reverse side).
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* **IMU:** ICM-20602 accelerometer (shares an interrupt line with the light sensor).
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* **Light Sensor:** XYC-ALS21C-K1 I2C ambient light sensor (shares an interrupt with the IMU).
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* **Leg LEDs:** 8x Blue LEDs running at 2mA (LED0603-RD).
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* **Eye LEDs:** 2x Addressable RGB LEDs (WS2812B-2020).
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* **Power & Battery:** TP4054 50mA battery charger, ME6211C22M5G-N 3V3 LDO, and XC6206P362MR 3V6 LDO (dedicated to the addressable LEDs).
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* **Connectivity:** Bluetooth with a minimal PCB trace antenna, USB-C for power/programming/serial, and a 5V rail to chain multiple devices together.
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* **Audio & Haptics:** Buzzer with a driving transistor, plus a footprint for a vibration motor (motor ultimately not installed in the final version).
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* **Interface:** 2x tactile user buttons, 1x tactile reset button, and an on/off switch.
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* **Debugging:** Base board debugging pins compatible with a standard ~$3 DAPLink debugger via pyOCD/OpenOCD.
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* **Aesthetics:** Silkscreen suction cups and mouth.
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## Fun Features & Known Flaws
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### The Fun Things
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* **Wobble Physics:** Because the assembled PCBs take the physical shape of an octopus, the whole device wobbles when shaken.
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* **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.
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* **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.
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### The Flaws (Lessons Learned)
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* **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!
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* **Haptics:** The vibration motor was mostly unnoticeable, leading to its removal from the final assembly. (Pins to connect a motor still exist)
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* **Logistics:** Transporting an assembled device safely is tricky.
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## Software
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Checkout [chill](https://git.aintmina.org/aintgit/chill) project for building zephyr app with MCUboot.
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<img src="pics/smack.gif">
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## History
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### Idea
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<img src="pics/paper_model_v1.jpg">
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### First prototype
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<img src="pics/prototype1-3.jpg">
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### Second prototype
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<img src="pics/Device1.jpg">
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### Final version
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<img src="pics/final_device.jpg"> |