Here's some more information on my
BIG LED CLOCK

I've always liked things with LEDs, preferably *MANY* (flashing) LEDs...
On my vacation in the summer 98' i started to think about building a big clock
with LEDs. The first thing to decide was: "Exactly how big should it be?"
I settled for approx. 80 cm wide and 30cm high. Quite big but not TOO big...
One thing I worked with for a few days was the mounting of the LED:s...
The solution I chose was quick, cheap and simple:
For each digit I drilled 5mm holes for all the LED:s in a sheet of black painted
plexiglass and mounted the LED:s. The I soldered the LEDs together in seven
segments (each powered with 12volt). Finaly I used a gluegun to fix each
segment in position.

BIG LED Clock Schematic and Sourcecode availiable for donload now!
Please don't complain if you don't understand this or if something isn't complete. These are my blueprints...

Backside if the clock. The four segments ar mounted on two strips of wood together with the "I/U" segment.
The PCB in the upper left corner is the CPU PCB. Above the CPU pcb there are two 3.5mm Phonopluggs that connect the
temperature sensors. Behind each segment there are a small driver PCB.

  
 

Detail of one of the segments. One of the IC's is a PCF8574 I2C I/O and the other one is a ULN2803 Darlington driver

Detail of the CPU PCB One PIC 16F84 and one PCF8583 RTC

The I/O-logic is "distributed"(!) Behind each digit I placed a small pcb with one
I2C 8-bit I/O chip and one driver IC (ULN2803). As each pcb has three
address straps, all four digits are exactly alike. I also builded a ":" symbol and
a small segment showing either an "I" or an "U" (Inne/Ute = Indoor/Outdoor)
These three (I/U/:) segments was connected to the unused outputs on three of
the digit pcb:s.

Temperature is read by two Dallas DS1820 digital thermometer-chips.
Even thoug I could connect both chips to one single I/O pin I decided to use
one I/O pin for each chip so that I wouldn't have to take care of the unique
ID-bytes in the chips. Quick 'n' Dirty... ;-)

The microcontroller, clockchip, 5v powersupply etc are placed on a separate
pcb. To this pcb the input power is connected and also three buttons which
are used for configuration and for setting the clock.

The software is quite simple... I'll probably publish it here later...

I've mounted the clock in a frame made of aluminium strips (normaly used for
flightcases). In front of the segments I've mounted a sheet of gray-tinted glass.

As I built this clock I learned how to use both I2C and Dallas MicroWire!
And at the same time I made the necessary routines for both protocols!


>>>Thougths of Enhancements<<<
Things I'll do when I get the time...
DCF-77 receiver, The clock will run at atomic accuracy!
LDR that senses the brightness of the light in the environment.
Dedicated powersupply (Now I use my lab-supply...)


Technical information:
    MicroController: PIC16F84 @4Mhz
    I/O: 4x PCF8574  I2C 8-bit I/O (one behind each digit)
    Timekeeper: PCF8583  I2C Clock/Calendar
    Temperature sensors: 2x DS1820
    LEDs: approx. 650pcs 5mm Red (The cheapest ones I could find ;-)
    Power: 12v @2A