[time-nuts] TNS-BUF update

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sun Aug 19 15:01:57 EDT 2018


There are some NIR sensitive photodiodes that take advantage of the NIR transparency of some black epoxies.
Bruce
> On 20 August 2018 at 02:48 Dana Whitlow <k8yumdoober at gmail.com> wrote:
> 
> 
> 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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