[time-nuts] Precisione GPS based led clock

Tom Van Baak tvb at LeapSecond.com
Thu Nov 3 14:56:49 EDT 2011

> How about using Binary for the last couple of digits? 4 LEDs
> for a digit in BCD. Saves on pins and wiring.

The pin savings is minor (10 bits of binary is 12 bits of BCD) and
the inconvenience to the user viewing the photograph is great. So
I rejected binary. Remember even 1950's frequency counters were
nice enough to display in decimal (1-of-10 neon lamps or dekatron
or nixie tubes).

If you're comparing LED segments vs. binary then, yes, it's a 7:4
advantage to do binary. But again, unless you are trying to create
a novelty or museum piece it's worth avoiding binary displays.

If you drive 7-segment LEDs with 4511 chips you get the latch, a
7-segment decoder, and the LED driver for free.

If you use 16- or 24-bit serial-parallel-latches or "port expanders"
then you only need 2 or 3 pins of the microcontroller. Use one or
more '595 or look at the wonderful chips by Unitrode/Allegro.

BTW, if 1/100th second is all that is needed for the photograph,
don't discount analog dials; that is, a synchronous clock with hour,
minute, second, and [60 Hz] cycle hands.


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