Bangle.js Minimal C Example Code

This is a minimal example of running your own barebones C code on Bangle.js 2, with support for Bluetooth, LCD, Button and Touchscreen.

Example code is based on nrf5x_17/examples/ble_peripheral/ble_app_uart/main.c (for BLE UART capability)

See https://www.espruino.com/Bangle.js2+Technical for full details of pinouts and hardware.

Building

• Download nRF5 SDK version 17 from https://www.nordicsemi.com/Products/Development-software/nRF5-SDK installed in the nrf5x_17 directory
• Ensure you have arm-none-eabi-gcc installed and nrf5x_17/components/toolchain/gcc/Makefile.posix is set up to point to it
• Get an nRF52DK wired up to the Bangle.js USB charge cable as shown in https://www.espruino.com/Bangle.js2+Technical#swd (while in theory you can develop wirelessly via DFU updates, it's no fun at all and you're liable to brick your device)

# make the software
make
# write the softdevice (only need to do this once)
make flash_softdevice
# write the actual firmware
make flash

Implemented

• Bluetooth UART
• Button
• Kick Watchdog timer once a second while button is pressed (long press still reboots to bootloader)
• Charging detect
• Backlight
• LCD screen (simple text, fillrect)
• Touchscreen

Not Implemented

• Accelerometer
• Magnetometer
• HRM

Notes

• We use software I2C for touch, and software SPI for the LCD screen just for simplicity (hardware would allow background updates to the screen)
• The LCD is using 4 bit mode (3 bit mode or black and white is possible - but again, simplicity)
• While on, the touchscreen draws ~1.5mA, and the backlight draws ~60mA