[time-nuts] Generating a solid PPS from 10Mhz source

Bob Camp kb8tq at n1k.org
Mon Jan 18 10:11:56 EST 2016


Hi

Back in the 70’s I was involved in making LCD watches. The whole “photo” 
issue had not been fully through through. One day our chief marketing guy for
the project was driving around in Phoenix AZ. He looks down and notices that 
his watch is dead. Pops out a spare, puts it on, confirms it it working. Hangs his arm out
the window and …. that one is dead as well.

We changed the die coat on the ASIC to an opaque version soon after that …

Light does indeed interact with semiconductors. It happens even on circuits that
you would not *think* are photo sensitive. Physics is nasty that way ….

Bob

> On Jan 18, 2016, at 6:45 AM, Poul-Henning Kamp <phk at phk.freebsd.dk> wrote:
> 
> --------
> In message <569BC23A.3030400 at arcor.de>, Gerhard Hoffmann writes:
> 
>> LEDs abused as References:
> 
> This is one of the most stupid ideas ever, because LEDs works both ways.
> 
> (Back when LED wrist-watches first came out, people soon discovered
> that they would reset themselves when photographed with flash.)
> 
> If you insist on using LEDs as voltage references, the first thing
> you need to do is to dip the LED in something which shields it 100%
> from incoming light *including infrared*
> 
> -- 
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> phk at FreeBSD.ORG         | TCP/IP since RFC 956
> FreeBSD committer       | BSD since 4.3-tahoe    
> Never attribute to malice what can adequately be explained by incompetence.
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