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nrf52-watch

Overview

This repo is, at present, a work-in-progress playground for designing and building a smartwatch based on the nrf52840 microcontroller from Nordic.

Parts

  • RayTac MDBT50Q nRF52840 Module
    • Main brains. nRF52840 chipset chosen for BLE capability and low (<1uA) sleep current.
    • This is the module used in the Sparkfun Breakout
  • Sharp LS018B7DH02 1.8" Memory LCD with FLExLight Frontlight
    • Always-on display.
    • Chosen for size and small power consumption.
    • The LS018B7DH02 isn't sold directly by Sharp, and no datasheet is currently available.
    • Unknowns are currently
      • Does the display require 3.3V or 5V power?
      • Does the display require 3.3V or 5V logic?
      • Does the display require a 1Hz or 60Hz square wave for biasing? 3.3V models tend to need 60Hz, but the 5V models need 1Hz
  • M41T62Q6F RTC
    • Realtime clock, for real timekeeping.
    • Chosen for small power consumption and footprint
    • This module can also provide the 1Hz or 64Hz square wave required by the memory LCD, which means fewer wakeups for the nRF52840
  • MCP73831T Battery Charger IC
    • Charges at 4.2V
  • USB-C port for power, charging, and data
    • I'm cheating here and using USB 2.0 Compatibility mode, so I don't get the benefits of USB-PD.

Power

  • Project will be powered by a 500mAh LiPo, which has a nominal capacity of 500mAh at 3.7V.
    • Battery chosen has built-in overcurrent and undervoltage protection circuitry, meaning that I don't have to design any.
  • Projected lifetime is >2mo, though it remains to be seen if this is possible

Manufacture and Assembly

  • Prototypes of the case and mechanical components will be 3D printed.
  • Once I have a design that I like, I'll send the files to Shapeways or ExOne to be 3D Printed in steel.

Software

  • To conserve power, everything will be interrupts-driven.
  • A decent amount of build hackery was needed to make the native version build with the dummy adafruit_gfx library

Credits / Inspiration

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