What Tinys.it is an open source Touch 3D printed LED watch with Atmega328P microcontroller programmed with Arduino.
32 LEDs in circle shows the time. The solid LED indicates the hours, while the blinking LED indicates the minutes.
The microcontroller has 32 pin, they aren't all I/O: only 25 pins can be used for the 32 LEDs and the touch sensor. To drive a larger number of LEDs with few pins i've used the Charlieplexing Matrix, in this way i can drive 6 LEDs with only 3 Pins.
The time is showed by touching the upper part of the watch.

For perfect timing i've used a 32.768 KHz Crystal connected to Xtal pins of Atmega328p running in asynchronous mode. In this way i can use internal 8Mhz oscillator as main clock of the microcontroller and the overflow of timer2 (used for the external crystal) as interrupt for increase the seconds.

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