<div>What is cheap, how many do you intend to build, will you build them all yourself or do you need to have them able to be built by others?</div><div><br></div><div><div id="mb">How directional do you need it to be, and what is the ratio between the light you want to detect and background or other sources you need to reject?</div></div><div id="mb"><br></div><div id="mb"><div id="mb">A lens on top of a photo diode, combined with a cover on top of the photo diode with a tiny hole in it might work. A pinhole instead of a lens?</div><div id="mb"><br></div><div id="mb"><div id="mb">A long tube is simple, but it has to be long *relative to the size of the light sensing element*. If you have a tiny tube then it can be shorter. A thick piece of plastic with a small hole drilled in it? If the hole is tiny relative to the plastic thickness that might be enough. Won't let it much light of course, but that might not be an issue. </div></div></div><div class="mailbox_signature"><br>Thanks,<br><br>gopi@iPhone<br></div><br><br><div class="gmail_quote"><p>On Mon, Jun 10, 2013 at 2:52 PM, Christoph Maier <span dir="ltr"><<a href="mailto:firstname.lastname@example.org" target="_blank">email@example.com</a>></span> wrote:<br></p><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;"><p>Can anyone on this list give me recommendations (nudge,nugde, Mitch
<br>Altman) how to build cheap photosensors (wink,wink, Jonathan Foote)
<br>that are highly directionally sensitive?
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