LED Watch 1: Preliminary Overview


The goal of this is to design a simple watch made from a single PCB and a watchband. In this initial version the time will be told using an RGB LED to tell an approximate minute time in color, and 4 LEDs to tell the hour precisely in a binary encoding.

Design Specification


  • All Surface Mount.
  • Easy enough to solder to act as an intro SMT soldering board.
  • Battery Life of 3+ months, preferably closer to the 1 year mark.
  • Simple and novel watch design


  • 4 bit binary hour counter, with LEDS.
  • RGB LED to tell part of hours
  • 3V coin-cell Battery Supply
  • 1 Button, to bring up and set display.
  • 32.768 kHz Crystal Oscillator driving an asynchronous clock
  • Utilizes low-power modes, for long battery life.

Time Display "Protocol"

I have spent a little bit of time designing a basic time display methodology. 4 LEDS represent the hour in binary form. The RGB LED represents the part of the hour divided up into 10 separate states as follows.

Colours (R,G,B) # of Minutes Passed
R 0
R G 10
G 20
G B 30
B 40
R B 50

Basic Layout

This is just a basic layout prone to be changed a lot.

Preliminary Parts List

Reference Description Distributor Distributor # Manufacturer Manufacturer # Datasheet Link Quantity Cost Per Part Cost Per Board
na ATTiny24A Microcontroller Digikey ATTINY24A-SSU-ND ATMEL ATTiny24A-SOIC14 http://www.atmel.com/Images/doc8183.pdf 1 1.01
na Side Actuated SMT Buttons Digikey P12279SCT-ND Panasonic Electronic Components EVQ-P7C01K http://industrial.panasonic.com/www-data/pdf/ATK0000/ATK0000CE20.pdf 1 0.74
na Green 0805 CHIPLEDS Digikey 475-1410-1-ND OSRAM LG R971-KN-1-0-20-R18 http://catalog.osram-os.com/catalogue/catalogue.do;jsessionid=B38D4035738FAE714C474120326E9384?act=downloadFile&favOid=02000002000009ee000100b6 4 0.09
na 32.768kHz Crystal Oscillator Digikey 300-8663-1-ND Citizen Fintech Miyota CMJ206T-32.768KDZF-UT http://cfm.citizen.co.jp/english/product/pdf/CMJ206T.pdf 1 0.83
na LED CHIP RGB 3.2X2.7X1.1MM SMD (1210) Digikey 516-1795-6-ND Avago Technologies US Inc. HSMF-C114 http://www.avagotech.com/docs/AV02-2451EN 1 2.03
na 20pF Capacitors 2
Battery Holder 2032 Digikey BC2032-E2-ND MPD BC2032-E2 http://www.memoryprotectiondevices.com/datasheets/BC2032-E2-datasheet.pdf 1 0.74

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