This is my second instructable. I just had a mood of making a digital watch. But wanted to make it a learning process. I already had a sanguino i could have easily used that Atmega644 chip. it would have been more than enough. But i wanted to try burning a Arduino bootloader and see if i could make it work. Well i did. I used a Atmega168 for this project.
I used 4 seven segment displays to display time in 24hr format. Here ii experimented with common anode and common cathode. Now i wanted to use other chips too and not just the Arduino which would have been the easier option. The chips i experimented with are 74LS47, 74HC154, 74HC595 ,4511 and 74HC139. The final compatible combination was common cathode with 4511 and 74HC139.
I used a RTC chip DS1307 to feed the time to the Arduino. I initially wanted to use millis() function in Arduino but it is not that accurate. Using RTC not only saved long coding but also has an added advantage of keeping the time in case the external supply is cutoff. It uses a 3v battery to do this.
Now I have used LEDs to point the time as minute and hour hands would do in an anolog clock. 60 Bi-coloured LEDs total which work on Charlieplexing.
Well if you are interested onwards you go.
Step 1: Parts List
Atmega168 (Duemilanove) + Holder
CD4511BE + Holder (CMOS BCD-TO-7-SEGMENT LATCH DECODER DRIVER)
74HC139N + Holder (Dual 2-to-4 line decoder/demultiplexer)
DS1307 + Holder (DS1307 64 x 8, Serial, I C Real-Time Clock)
Standby Arduino board to Burn bootloader in Atmega168 (optional if Already hav a chip with Arduino bootloader in it)
Breakout board + USB wire
Common Anode 7 segment display (4)
32.768 Khz watch crystal
9v battery + Plug
3v coin cell +Holder
Push button switch (Reset Arduino)
22pf ceramic capacitor (2)
100nf ceramic capacitor (3)
100uf electrolytic capacitor (2)
2.2 Kohms resistor (2)
10 Kohms resistor
5mm Bicolour LED (60) (There are different types see further for more information)
2mm thick Plexiglass
Glass paint kit
3/4th inch Nut and Bolt
Hook to hang by a nail (I made one fron plexiglass pieces)