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 <[email protected]> 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 <[email protected]> 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 <[email protected]> > > wrote: > > > > > -------- > > > In message <[email protected]>, 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 > > > [email protected] | TCP/IP since RFC 956 > > > FreeBSD committer | BSD since 4.3-tahoe > > > Never attribute to malice what can adequately be explained by > > incompetence. > > > > > > > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to http://lists.febo.com/mailman/ > > listinfo/time-nuts_lists.febo.com > > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there.
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