[time-nuts] Precisione GPS based led clock

Pieter ten Pierick time-nuts-mail at tenpierick.com
Thu Nov 3 14:01:03 EDT 2011


Hi,

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

I had the same idea, although my idea was to just make it completely
binary and use OCR on the photograph to find the time.
Maybe adding 2 surrounding always-on other colored LEDs to frame the
sequence would be nice?

Greetings,
Pieter.

>
> Robert G8RPI.
>
>
>
>
> ________________________________
> From: Tom Van Baak <tvb at LeapSecond.com>
> To: Discussion of precise time and frequency measurement
> <time-nuts at febo.com>
> Sent: Thursday, 3 November 2011, 16:29
> Subject: Re: [time-nuts] Precisione GPS based led clock
>
> I also have had need of a high resolution display clock for
> photographic time stamping.
>
> For those of you working on this make sure not to use a
> LCD or VFD display. The response time is too slow. Also
> you can rule out any sort of TV display.
>
> If using LED make sure not to multiplex the digits. This is
> a common trick, especially when using microprocessors,
> and works well for human eyes, but fails completely with
> high resolution photos.
>
> So having ruled out everything but direct drive LED the
> only other concern is to make sure the decade counters
> which drive the display are synchronous or at least that
> all the digits are latched at the same time. Otherwise you
> get false readouts due to ripple carry or sequential scan.
>
> Be careful using a microprocessor for this. For millisecond
> displays you need a total of 21 pins; for microseconds you
> need 42 pins. An external serial-parallel (e.g., shift register
> with latch) chip might be safer since neither a PIC nor an
> Arduino can update that many pins in one instruction.
>
> /tvb
>
>
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