Bangle.js Technical Information

For general Bangle.js information, try the Bangle.js 1 or the Bangle.js 2 pages

This page contains detailed information on Bangle.js's 1's internals. Click here for Bangle.js 2. If you're just writing JS then you should have no need for this information, but if you plan on modifying the Bangle.js firmware it might be of interest.

Contents

• Features
• Software
• Hardware
• GPS
• GPIO
• IO Expander
• SWD / Programming
• Heart Rate monitor PCB
• Charging pins

Features

• IP68 Waterproof (everyday use, not swimming or baths)
• Nordic 64MHz nRF52832 ARM Cortex-M4 processor with Bluetooth LE
• 64kB RAM 512kB on-chip flash, 4MB external flash
• 1.3 inch 240x240 16 bit LCD display with 2 zone touch
• GPS/Glonass receiver (UBlox)
• Heart rate monitor
• 3 Axis Accelerometer (with Pedometer and Tap detect)
• 3 Axis Magnetometer
• Vibration motor
• 350mAh battery, 1 week standby time
• 5 x 5 x 1.7 cm case, plastic with stainless steel ring
• Can be disassembled with just 4 screws

Software

Where mentioned in the source code or filenames, Q3 references Bangle.js 2, and F18 references Bangle.js 1.

The Espruino version for Bangle.js has a few specific modifications:

• jswrap_bangle.c contains all Bangle.* functions and pretty much all Bangle.js functionality.
• Some functionality (like menus) is in JavaScript which is built into the firmware. Those JavaScript files are here
• BANGLEJS.py describes the build
  • The SPIFLASH device causes SPIFLASH_BASE to be defined, which enables external SPI flash memory support in jshardware.c
• The bootloader starts at 0x7A000 (4k less than the standard SDK12 bootloader) because it was originally an SDK11 device

Hardware

Want to get inside? Check out the Bangle.js Disassembly page

• KX023 accelerometer
• GMC303 3 axis compass
• BD 1668 heart rate sensor (HRM) (no datasheet). All analog - op-amp comparing two wavelengths of light
• 32 mbit flash - similar command set to Macronix MX25
• 240x240 LCD with ST7789 driver used in 8 bit parallel mode
• Holtek touch controller - probably the BS83A02A with 2 zone on/off
• GPS is UBlox UBX-M8130
• 502527 Lithium ion battery

GPS

As above the GPS is a UBlox UBX-M8130

On boot, it reports: ROM CORE 3.01, PROTVER=18.00*11

Espruino handles reception and parsing of NMEA data from the GPS UART when Bangle.setGPSPower(1) is called.

However it is possible to also send UBLOX UBX commands to configure the GPS - see https://github.com/espruino/BangleApps/blob/master/testing/GPS-comms.js

GPIO

There's IO connected to the nRF52, plus an IO expander to provide power to some other things.

nRF52

Pin	Name	Notes
D0	LCD_D0	Bits 0-7 all set together via (char*)P0_OUT
D1	LCD_D1	Bits 0-7 all set together via (char*)P0_OUT
D2	LCD_D2	Bits 0-7 all set together via (char*)P0_OUT
D3	LCD_D3	Bits 0-7 all set together via (char*)P0_OUT
D4	LCD_D4	Bits 0-7 all set together via (char*)P0_OUT
D5	LCD_D5	Bits 0-7 all set together via (char*)P0_OUT
D6	LCD_D6	Bits 0-7 all set together via (char*)P0_OUT
D7	LCD_D7	Bits 0-7 all set together via (char*)P0_OUT
D8	LCD_DC
D9	LCD_CLK
D10	LCD_CS
D11	TOUCH RIGHT	inverted
D12	Battery charging when low	Input pullup
D13	VIBRATE - active high
D14	I2C SCK
D15	I2C_SDA
D16	TOUCH LEFT	inverted
D17	Flash D3 (RST - connect to VCC)
D18	Speaker (if included), otherwise inverted output on HRM PCB
D19	Flash SCLK
D20	Flash D1 (MISO)
D21	Flash CS
D22	Middle button	inverted
D23	Top button	inverted
D24	Bottom button	inverted
D25	GPS RX
D26	GPS TX
D27	Flash D0 (MOSI)
D28	IO expander reset
D29	HRM Analog
D30	Battery Level	0.51=low, 0.62=good
D31	Flash D2 (WP - connect to GND)

IO Expander

Mask	Description	Default value
0x01	GPS	0
0x02	NC
0x04	NC
0x08	NC
0x10	NC
0x20	LCD backlight	1
0x40	LCD reset	1
0x80	HRM	1

Click on the pictures above for more zoomed in information. Also check out this excellent forum post for even more detailed reverse engineering.

SWD / Programming

You can completely reprogram (and even debug) the nRF52 chip inside Bangle.js with the SWD pins. These are on the circuit board under the LCD.

You can carefully pull up the LCD and cut/tear through the foam tape holding it on. Underneath that you'll find 4 pins, labelled as follows:

You only need GND, SWDID and SWDCLK (VDD is not required).

Heart Rate monitor PCB

On the bottom right of the PCB (by the label R6) are the two pads for the speaker. The one labelled + goes directly to 3.3v, and the one next to it goes to pin D18 via a transistor.

As such, D18 is inverted, and can only be used as an output - however it is powered (pulldown via MMDT3904) so is able to drive reasonably high loads (up to ~100mA).

The heart rate monitor itself is powered from the IO expander, and has just a single analog output, which is D29.

Charging pins

The two circular gold pads interface with the charging circuit. The right-hand one (with them at the top of the watch) is connected to GND, and the left-hand one goes to the charging circuitry.

I2C

SCK=D14, SDA=D15

• 0x0C - GMC303 magnetometer
• 0x1E - KX023 accelerometer
• 0x20 - io expander
• 0x7C - Unknown. Only checked once by OEM firmware.