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SUhr Is a BLE-Enabled, ATmega1284P-Powered Smartwatch

SUhr Is a BLE-Enabled, ATmega1284P-Powered Smartwatch


Inspired by another MemoryLCD watch from a few years ago, the Chronio, Hackaday user vch1 has created a BLE-connected, AVR-based smartwatch called the SUhr.

Not looking for a minimalist design, the wearable device is packed with features including vibration, backlight, an accelerometer, a magnetometer, and more. As the project is a year and a half in the making, it has been through a few iterations, attempting to work all of these electronics into a case suitable for everyday use.

Schematics for the current version are available in vch1's write-up, as well as the .stl files for the case, which were printed with HP Multi-Jet Fusion. The unit embeds an LS013B7DH03 128x128 display, with backlighting supplied by FLEx lighting.

The LCD necessitates some RAM for the framebuffer, thus the choice of ATmega1248P. An internal RC-oscillator MHz serves as the main clock for the microcontroller and is calibrated to approximately 7.3728MHz on each boot.

The watch employs an integrated module, the Microchip RN4871, which means its power consumption will never be as low as an nRF or STM32 standalone solution. It also means a 3.3V regulator is needed, as it cannot be used with the maximum 4.2V expected from the lithium-ion cell.

The Li-ion cell is used over a more commonly available coin cell due to the higher consumption. The main sensors, e.g. magnetometer and accelerometer, are provided by an LSM303.

The multiple iterations of the project enabled some trouble-shooting to be done on hardware issues, in addition to the form factor of the watch — the original circular case with quite a large diameter and body height due to the Li-ion cell.

The first model lacked a reset pin for the RN4871 module, as well as a few other kinks to be worked out with programming and design.

The software components started as a project comprised of readily available Arduino libraries, which at least allowed for verification, grew as the project continues over the course of a year, and eventually became unwieldy enough to constitute a rewrite. Now the code is comprised of apps, libraries with functions following a template, which are called by the main script.

The second version of the hardware is a smaller rectangular body sealed with o-rings for buttons and glass and a silicone conformal coating on the PCB.

Charging is not done via a USB socket but with 9 pogo pin pads on the bottom of the watch that connects to the pogo pins in a dock. The PCB is also more compact, as can be seen in the schematic. Both the code and hardware are still works in progress, but it is certainly an interesting project to follow.

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