[time-nuts] FE5680 missing PPS soln
robkimberley at btinternet.com
Fri Feb 3 13:42:29 UTC 2012
You need to check your maths...
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Attila Kinali
Sent: 03 February 2012 12:55
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] FE5680 missing PPS soln
On Fri, 3 Feb 2012 09:50:52 -0000
"Rob Kimberley" <robkimberley at btinternet.com> wrote:
> Mine was a green LED out of the junk box, but I did use 330R in
> series. 1k8 seems rather large.
Then i'm not surprised that your FE-5680 refused to work :-)
Just calculate: 5V supply, approx 2V LED voltage -> 3V over the resistor.
3V/330R = 90mA. As i wrote already, the 74AC240 has it's absolute maximum
rating at 50mA. For a general logic output, i wouldn't recomend to draw more
than 10mA (as Bob Grant wrote, the lock signal doesn't seem to pass trough
the 74AC240). Hence, i would say that 330R seems rather small :-)
Keep in mind that you drove circuit at over current for quite a long time.
The circuit is most likely damaged (if they dont have an over current limit,
which i doubt). If for an unknown reason the lock signal fails in the
future, it might be due to this.
The trouble with you, Shev, is you don't say anything until you've saved up
a whole truckload of damned heavy brick arguments and then you dump them all
out and never look at the bleeding body mangled beneath the heap
-- Tirin, The Dispossessed, U. Le Guin
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