qron0b is a sleek and low-power digital binary wristwatch designed to deliver timekeeping in a minimalist format. Featuring an Attiny24A/44A/84A microcontroller and a DS1302 real-time clock (RTC), the watch displays the current time using binary coded decimal (BCD) format on an integrated 4x4 LED matrix, driven by a reliable 74HC595 shift register. The device is powered by a single CR2032 coin cell battery, ensuring an extended battery life that allows it to function for months without requiring a battery change.

Repository Contents

The repository contains several key components for users and developers:

• pcb/: Contains the KiCAD project files for the qron0b PCB design.
• cad/: Includes FreeCAD files along with .stl and .step formats for 3D printing the watch case.
• firmware/: Provides the source code for the watch's firmware, crafted in bare-metal AVR C.
• assets/: Features screenshots and render files referenced in the README.

Key Features

The qron0b's firmware is minimalistic, primarily focusing on two main functionalities:

1. Reading Time
2. Setting Time

The watch defaults to a sleep state, with the CPU in power-down mode and the display off. Activating the onboard button wakes the CPU, briefly displaying the current time for 10 seconds. Time adjustment is possible while the watch is active by a long press of the onboard button.

Reading Time

Time is presented on the LED matrix using BCD representation across four columns in the format HH:MM. Each column indicates:

• Tens of Hour (Leftmost Column)
• Ones of Hour
• Tens of Minute
• Ones of Minute

Here's a visual representation of how the time is read:

Setting Time

To set the time, long press the onboard button while the watch is active. The LED matrix will flash to indicate that the watch is in edit mode. The user can cycle through each digit and adjust the values by pressing the button, following the sequence and saving changes with a long press on the final digit.

Hardware Design

The PCB Design of qron0b is created using the free software KiCAD. Review the source files available in pcb/.
Below are schematic and PCB snapshots contributing to the design:

Mechanical Design

The watch case for qron0b is designed in FreeCAD, consisting of two parts: a base and a top cover, which secure the assembly through a simple clip mechanism. The bottom portion accommodates 22mm GT2/GT3 watch straps. Details for CAD files and 3D print formats can be found in cad/.

Firmware

The qron0b firmware, designed for efficiency at only 1916 bytes, operates seamlessly on the ATtiny24A. Further information is available in the firmware section of this repository found in firmware/.