Simple Binary Watches with 4 LED(1/5, 2/10, 4/20, 8/40), it mean 5 minute accuracy indicate.
Every 0.5 sec CPU wake up(cycle iteration time 100 nS) and increase milliseconds value and come sleep mode(3 uA).
If you press button "TIME();" it show hours and minutes(0.5 seconds per value) in binary mode in 4 LEDs.
PCB Up side:
PCB Down side:
PCB size 27 mm in diameter(size little biger CR2032 battery):
The thickness of the board is recommended to take 0.8mm otherwise it may not fit into the case.
Files for fabrication:
https://github.com/techn0man1ac/ATtiny13BinaryWatches/tree/main/PCB
Fresh board project here:
https://oshwlab.com/raznie.podelki/attiny13binarywatches
It's have simple schematic, there are 15 components in total:
Here is pinout for AVR ISP programmer - MOSI ATtiny13 -> MISO programer(Digital Pin 11), MISO->MOSI(Digital Pin 12), SCK->SCK(Digital Pin 13) RES->Reset(Digital Pin 10). How to flash ATtiny13 with Arduino:
https://www.hackster.io/taunoerik/programming-attiny13-with-arduino-uno-07beba
ATtiny13 core selections:
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Board: ATtiny 13
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BOD: BOD Disabled
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Clock: 1.2 MHz internal osc.
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Compiler LTO: Enable
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Port: (Your Arduino port)
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Programmer: Arduino as ISP
Source code(for Arduino IDE - "t13B Watches.ino") here:
https://github.com/techn0man1ac/ATtiny13BinaryWatches/tree/main/t13BinWatches
It's project full open source(PCB and code).