Arduino 7 segment Displays Digital Clock With Charlieplexing LEDs

  
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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
Arduino 7 segment Displays Digital Clock With Charlieplexing LEDs - schematic

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. I have made the circuit in Eagle but sadly I am not thatproficientin using the software (Which is next on my TO LEARN  list) so I didn`t make the board. I have attached the schematic i made on Eagle. U can use it to make the board. I used Express PCB to create the PCB. I have also attached this. pcb file here. You can eitherprint this file directly and make a pcb from a copper clad or build a board from Eagle and get it made professionally. 1) In express PCB fileI`veused JMP at some places. It means you have to use wires to short the two pads. This was necessary since i used a single sided PCB. Confirm where to connect wires from the circuit diagram. 2) At digital pin 0 and 1 i have used jumpers. This is VERY IMPORTANTas the LEDS have to...



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