FreeTrack Forum

Hi all.
Since some of us, like me, can not find in our local store the holly grail of freetrack-- i.e. the osram SFH 485 P, (which has an wide angle beam, around 80 degrees, perfect for a freetrack tracker) I thought to help somehow.
 I do not want to invent warm water, the metod described here is well known to freetrack users (infact I learned from this forum, back in the old days). I just want to help the newer users or the ones with less practical skills.

The most widespread ir diode is the one with narrow ir beam, available in every electronics shop I entered, can be found in any ordinary remote control, in toys or even in some optical mouse...in short the world is full of them   .Common caracteristics are: forward voltage 1.4-1.6 v; forward current aprox 20 mA
Either it's transparent or coloured, this little "animal" can  be recognised with ease since has a long 'body", unlike SFH485, which is clearly shorter.



  Exactly here is our trouble: the long plastic body acts like a converging lens channeling the infrared ray into a narrow (but relatively powerful) beam, about 20-30 degrees wide...can be perfect for a remote control, but when used for freetrack is almost useless because moving our head more than 20-30 degrees (relatively small move) will cause the tracker not to be visible for camera anymore.



So what can be done? Should we lose our track?? NO way!
One option is to sand the surface of whole body of led forcing the ir light to exit in any direction due to diffraction, sounds ok...but the main beam will still be channeled trough lens, and sanding will only render the ir led fainter...
 Another option is more drasticall : let's get rid of that "lens". Cut it.
Using a minisaw or a dremell like machine cut the plastic lens of a led, about1-2 mm above the led chip, BUT be careful not to reach the chip surface or else..or else you'll have one led less.






Now you should have a nice shorter led when compared with his brother. Already a much wider beam (80+ degrees) BUT with a slight loss of ir light intensity...practically negligible.



For a nice finished product, you can sand perfectly flat  the cut edge of led using smoother and smoother sandpaper and clarify the pastic, allowing the ir light to pass more easily.



IF you are quite a maniac, then you can try to restore (somehow) the rounded profile of the led: first using coarse sandpaper to make the shape,



then smoother sandpaper to "clarify" the plastic.



That way the beam will have some slight focus, improving led visibility.
Finished product...kinda look like that illusive sfh485..    




Every tracker built by me was constructed using common ir leds prepared by the metod above, and those are working flawlessly from day one, leds are visible to camera even above 90-100 degrees, way beyond freetrack limits.
So, anyone around the globe can build a tracker, with a little care, JUST BUILD IT.

Hope this little tutorial helped in anyway.
best regards.

Volans;

Great tutorial for those who cannot get the Osram SHP485P.
The pictures will help others immensely!

This is slightly off topic, but I'm wondering about some LEDs I have from an IR RC helo controller, theres 3 of them wired consecutively, it uses 6 AA batteries, and there's 2 resistors I can see that would connect to them, but cant be sure due to the IC in it, now I cant read these because they use slightly different colours then normal, one of them is with tolerance last (burgandy,black,gold,gold) and the second one is (burgandy,black,black) both seem to have cement cases, any clue witch one it most likely is?


EDIT

never mind, dosn't use a resistor, I now have a voltage regulator

nice tut... wish i would have done this rather than paying for SHP485P LEDs