[time-nuts] Precisione GPS based led clock

[shalimr9 at gmail.com]

Tom,

I checked the spec for the VFD display I am using with my GPS Monitor, but there is no spec for how fast the segments are updated. I know that the external interface is much faster than that of the LCD, even though the commands are the same and the two are generally compatible. Visually, the VFD display is much faster, but without a high speed camera, I am not sure how to check if it would be fast enough.

Looking at the number of pins on the display itself, it must be multiplexed, so that may not be fast enough for your application.

Didier KO4BB

Sent from my BlackBerry Wireless thingy while I do other things...

-----Original Message-----
From: "Tom Van Baak" <tvb at LeapSecond.com>
Sender: time-nuts-bounces at febo.com
Date: Thu, 3 Nov 2011 09:29:42 
To: Discussion of precise time and frequency measurement<time-nuts at febo.com>
Reply-To: Tom Van Baak <tvb at leapsecond.com>,
	Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
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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