My Garage under attack from LEDs.
PHASE II Electronics.
Many circuits are available to drive a LED clock. I have here 3 or 4 varieties of ICs dedicated to just such a task. Using one of them would have made the project progress quickly, but would have resulted in little learning. I decided to build a circuit and program a PIC Microcontroller to keep the time and drive the LEDs.
Sidetracking a bit: PICs & Me, A Brief History:
In early 2000 I decided to dig into PIC Microcontrollers. I had read numerous articles about them, and saw that they could do in a chip what often took many chips or was even impossible to do without microcontroller intelligence. I ordered a tube of 16F84-10 chips from Digikey. The programmer for these chips is $200.00 which was about $180.00 more than I had left to spend at the moment, so while the chips were on their way here I set out to build a programmer for them. I looked over a huge number of websites, and found a programmer I liked.
The programmer and software I settled on is called FlashPIC. The programmer circuit is straightforward to build, and connects to the printer port of my PC. The author is a friendly bloke from New Zealand, and even kept his sense of humor when I kicked him around a bit by email! The software is shareware and the downloaded version is fully operational. Registering it was $39.00, a bargain compared to buying a $200.00 programmer, so I sent him the money. Registering removed a 30-second opening nag, and gives Bryan the ability to continue developing wonderful software. I see he has now reduced the price a bit, removing any excuse for not registering it.
I had a nice aluminum case here that I'd picked up at a Hamfest, it originally
housed a 1970s vintage digital Volt meter. A new faceplate cut from a
chunk of glass-epoxy circuit board, replace it's
"guts", add a couple ZIF sockets, and it formed a wonderful PIC
A little hunting around the Net gave me oodles of PIC source code examples. With a bit of soldering and a bit of learning I soon had all sorts of interesting PIC gadgets.
MEANWHILE BACK AT THE GARAGE CLOCK....
I decided to use a PIC 16F877 chip to control the clock. It has more I/O pins than the 16F84, has a built-in serial port, and more RAM.
The next decision I faced was how to make the clock keep time accurately. A clock of that size for public viewing obviously needs to always be correct.
0) That dumb idea about having 1 fixed time . . . "Twice a day" is NOT the same as "always."
1) Create a software loop that takes 1 second to execute, adjust the clock as often as needed for drift.
2) Power line frequency is a handy source of 60 Hz, but power here is not particularly reliable.
3) WWVB broadcasts the time at 60 KHz, but it is prone to interference.
4) A crystal oscillator at 10 MHz could be zero beat to WWV yielding a local clock frequency that was close to perfect.
GPS always supplies the exact time to the nearest couple of milliseconds.
I decided to spend a few dollars on the project and go with GPS.
PAGE 4 GPS
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