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ATtiny402 Binary Wristwatch

A minimal binary wristwatch powered by the ATtiny402. Pressing the left button will make the LEDs light up in BCD digits for a few seconds before automatically turning back off to conserve power. Based off of some initial measurements, a CR1216 battery should be able to keep the watch powered for multiple months of use. The full project, including source code, is on my GitHub.

Enjoy!

File descriptions

watch_body.3mf: The main body of the watch that holds the PCB. Designed to be used with a full-loop style, 15mm watch band.
watch_screw.3mf: A screw-in cover to allow access to the battery compartment. Has a large slot to allow it to be unscrewed with coins or can tabs for convenience
gerbers.zip: Design files for the PCB itself that can be sent to a PCB fabrication service. I used DKRed for the PCB in the picture, but something like OSH Park's After Dark PCBs would also work great!

Print settings

I printed the watch with the face side up and top layer ironing enabled for quality. I used the following settings:

0.4mm nozzle
0.45mm line width
0.1mm layer height
10% gyroid infill
Snug supports, auto generated
Topmost surface ironing, 0.1mm spacing and 15% flow rate

Additional parts needed

You'll need a CR2032 battery, the watch face PCB, a 18mm watch band, and some way of programming the ATtiny402. I just used an Arduino Uno and followed this tutorial. You'll also need the following electronic components:

Component	Count	DigiKey Part Number
ATtiny402	1	ATTINY402-SSNRCT-ND
Push button	2	P13348SCT-ND
Battery holder	1	BK-916-CT-ND
Blue LED	12	1830-1068-1-ND
47\u03a9 resistor	4	10-ERJ-H3GJ470VCT-ND
4.7k\u03a9 resistor	1	10-ERJ-H3GJ472VCT-ND
10k\u03a9 resistor	2	10-ERJ-H3GJ103VCT-ND

Colophon

The watch body was designed using onshape and has a parametric field for watch band width. If you want to make any alterations to the design, it is accessible here. The PCB was designed using KiCad EDA, and the source code was written in VSCode.

License Info

This work is published under a Creative Commons Attribution-NonCommercial 4.0 International License. use, and modify this work for any non-commercial reasons as long as you give appropriate credit. The author additionally grants permission for PCB and CAD design files to be sent to third-party manufacturers for fabrication as long as these fabricated parts or assemblies containing these fabricated parts are not later resold for profit.

Change Log

1.0.0 (6/9/2024): Initial release
2.0.0 (6/13/2024): Higher LED duty cycle, calibration support, CR2032 watch battery, 15mm to 18mm strap, and generally nicer looking PCB

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Binary Wristwatch

Model files

watch_screw.3mf

watch_screw.3mf

watch_body.3mf

watch_body.3mf

Other files

gerbers.zip

gerbers.zip

Model origin

License