[time-nuts] FE5680 missing PPS soln

[Don Latham]

I'm using a 556 dual timer, one section as an inverter to drive a lock
led, and the other section as a pulse stretcher to drive a 1 pps led.
Let's get on with it.
Don

Attila Kinali
> 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.
>
> 			Attila Kinali
> --
> 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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Dr. Don Latham AJ7LL
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