On Nov 18, 2009, at 4:52 AM, Vasile Surducan wrote:

>>> assuming you want to build it from scratch, how many IO pins will be
>>> necessary for a 7 seg clock displaying:
>>> dd:mm:yyyy     hh:mm:ss:tt   totaly16 digit
>>> where the format displayed is day:month:year   
>>> hour:minute:second:milisecond

I think you need another "t" for milliseconds.  Did you mean  
centiseconds?

I count 16 by 7 pins for conventional multiplexing, although 16 digits  
is perhaps pushing the number of digits that can be easily  
multiplexed.  Cheating might be possible; I suspect you can hardwire  
the first two digits of yyyy, for instance, and you might as well HW  
the lsd of fractional seconds to an 8...  But it's probably not worth  
it...

Charlieplexing would rule out most multidigit displays, which would  
probably be a bad thing when you have this many digits  (although,  
you're also not using standard formats, so perhaps you don't have that  
option anyway.)  Charlieplexing is also more useful when you have  
fewer total segments and can get away with small numbers of  
simultaneously lit LEDs...

Throw in some cheap 16F59s as display controllers, and go with the  
"one to two comm lines per display controller" philosophy...   
Multicore is all the rage.

BillW

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