This repo is, at present, a work-in-progress playground for designing and building a smartwatch based on the nrf52840 microcontroller from Nordic.
- 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.
- 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
- 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.
- Side buttons (required since the display is not a touch screen) will be on separate PCBs, connected via JST-SH cables to the main PCB. This allows me to use normal PCB buttons rather than right-angle ones, and gives some flexibility in mounting the main PCB.
Since there isn't code written yet, this section is largely my notepad on ideas and framework setup.
- To conserve power, everything will be interrupts-driven.
- PlatformIO doesn't have a builtin for the sparkfun dev board I'm using, so the packages/ directory and corresponding lines in platformio.ini are a workaround to keep the repository as portable as possible
- A decent amount of build hackery was needed to make the native version build with the dummy adafruit_gfx library
- This project uses open-source code from the following projects. Licenses are included alongside code where applicable.
- This project took inspiration from these projects: