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 <p...@phk.freebsd.dk> wrote: > -------- > In message <1818735266.3837388.1534666949...@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 > p...@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. > > _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
