It would be very easy to use a constant current to drive the LED and simply
short it periodically to provide the blinking without supply current
variations. You would still have short transients in the drive circuit, but
these should be much easier to filter.
Didier KO4BB
Sent from my BlackBerry Wireless thingy while I do other things...
-----Original Message-----
From: Magnus Danielson <mag...@rubidium.dyndns.org>
Sender: time-nuts-boun...@febo.com
Date: Wed, 16 May 2012 09:51:00
To: <time-nuts@febo.com>
Reply-To: Discussion of precise time and frequency measurement
<time-nuts@febo.com>
Subject: Re: [time-nuts] Why are 1PPS signals so skinny?
On 05/16/2012 05:25 AM, Hal Murray wrote:
>
> rich...@karlquist.com said:
>> FWIW, the E1938A oscillator control board had a "happy light" LED that
>> flashed 1 time per second, and sure enough this corrupted the power supply
>> and affected some applications. We added a command to turn it off.
>
> Why should lights blink when they are happy?
>
> Your eye is real good at noticing blinking things. Why not use blinking for
> things that are broken and need attention?
>
> Of course, with a PPS, blinking is an obvious thing to do: 1 resistor, 1 LED,
> your eye does all the work.
>
> I built a converter from blink on happy to blink on sad. I've been happy
> with it.
If you have a timer trigger that invert the LED drive, when it gets
stuck for whatever reason, then you will notice the lack of blinking.
This is why happy blinking is being used. It's really a form of simple
software debugging tool in its simplest form.
You could get a watchdog timer that would trigger an unhappy blinker.
More hardware.
Cheers,
Magnus
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