[time-nuts] TNS-BUF update

Dana Whitlow k8yumdoober at gmail.com
Sun Aug 19 10:48:12 EDT 2018


Be watchful about the black epoxy.   It may just be a dyed (otherwise
clear) epoxy,
and some of the black dyes in common use pass near IR quite readily.  This
would
probably be most troublesome if the ambient light source were of the
incandescent
persuasion.

Also, small diodes in clear packages can also make photodetectors.  I once,
in
desperation at a customer's site, successfully kluged a slightly
sub-nanosecond
detector out of a 1N914 (or one of those types like that) and a 9V battery.

Dana


On Sun, Aug 19, 2018 at 8:15 AM, Didier Juges <shalimr9 at gmail.com> wrote:

> That's a very good point. I have used LEDs as photocells many times, the
> first time was in 1974 when it was easier for this university student to
> get LEDs than photocells.
>
> I have also made a bi-directional optically isolated data link using a
> single fiber optic cable and two fiber optic transmitters (LEDs) in the
> HFBR-500 series.
>
> A couple coats of black paint, or a dab of black epoxy covering the LED
> should work. Include the back side of the PWB for good measure, this is
> time-nuts :)
>
> Didier KO4BB
>
>
> On Sun, Aug 19, 2018, 3:38 AM Poul-Henning Kamp <phk at phk.freebsd.dk>
> wrote:
>
> > --------
> > In message <1818735266.3837388.1534666949194 at webmail.xtra.co.nz>, Bruce
> > Griffit
> > hs writes:
> >
> > >It exploits the fact that for a RED LED at least the difference
> > >between the LED forward voltage and the transistor Vbe is ~ 1V and
> > >has a fairly low tempco and has low noise (at  least for RED LEDs).
> >
> > ... in darkness.
> >
> > When using LEDs this sort of way, they should always be totally
> > shielded from all external light.
> >
> > --
> > 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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