Trying (and failing) to make a LED circuit for TrackIR clip

Technical Support
#1

TrackIR is very helpful, but pricey, so i decided to make my own. The modified camera and clip body is done.

I am trying to make a Trackir clip and after assembly i found out the LEDs do nothing.
LEDs used: https://www.conrad.cz/p/osram-sfh-485-p-ir-reflektor-880-nm-40-5-mm-radialni-153831
Technical specification: https://asset.conrad.com/media10/add/160267/c1/-/gl/000153831DS01/list-technickych-udaju-153831-osram-sfh-485-p-ir-reflektor-880-nm-40-5-mm-radialni.pdf

Originally i used 18 Ohm resistors, (the idea was for the LEDs not to be too bright.) After i tested them, i instaled 10 Ohm resistors. They are salvaged from old electronics, i think they are 10 Ohm based on the markings: brown, silver, black, black, brown. The 10 Ohms come from a led resister calculator: http://ledcalc.com. The whole thing is powered by two AAA batteries.
My soldering isn’t very good, but should be good enough. The only think i can think of is that i chose the wrong LEDs.

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#2

Hi Airtria, it has been a while since I made the one I have but it works perfect. I can’t find the link or the site of the bulbs that I bought. I did find this and I recall that this was really handy: A complete guide to set up Head-tracking (Opentrack) - Manuals, Tutorials, Guides and Tips - IL-2 Sturmovik Forum

I’m terrible at soldering aswell but I’ve not had any issues, I plug it into the USB port and use an old ps3 camera.
If you’re also using a ps3 camera then you’ll find some sites that say the newer models don’t work. They do, you just have to place the IR filter from the floppy drive over the outside and glue to frame.

The biggest issue I’ve had is securing the device that holds the lights to my headset. I’ve got an Asus Rog Centurion and the frame is too thick above the ear pieces. I tried almost everything and have a temp solution (which will likely end up being permanent because it works).

I have a spare ps3 monitor mount if you need one? If you’re in the UK it’ll not cost much to post.

The whole setup cost me £23 which I count as a win.

#3

Are the batteries in series or parallel?
Looks like your LED requires a minimum forward voltage of 1.5V (at 100mA).

Parallel:
If you are using a pull up resistor, you are likely not meeting that voltage differential requirement.

Series:
You likely have an error in your circuit (soldering or otherwise)
Note that resistors are actually very fragile - you may be better off getting some new ones instead of salvaging them.

Side note: The correct way to drive LED brightness is with a PWM circuit, not through voltage modulation.

I have a background in electromechanical engineering and am happy to help if you need any assistance debugging (time permitting).

#4

The batteries are in a holder: https://www.conrad.cz/p/micro-bit-ki-2271-bateriovy-drzak-2x-aaa-d-x-s-x-v-53-x-25-x-13-mm-1665590, pretty sure they are in a series. With the 18 Ohm resistors, is the LEDs not lighting up at all an expected result?

#5

That looks like it would be in series.
So i would expect the LED to power up.

Worth noting the IR LEDs are not in the visible spectrum so … if you aren’t using a camera to check luminance you’re not going to know if its on or not.

Fun tip - phone cameras will pick up most IR emitters.

#6

I am checking if the LEDs are powered up with a phone, that can see IR, not all phones can. I have tasted the camera for the tracking with a remote and it can see IR. The camera is a PS3 EYE camera with tape from an VHS. The calculator recommends 10 Ohm, 0.125W resistor, after a lot of googeling i found those. I will order the resistors and new LEDs just to be sure, should arrive on tuesday.

#7

If the tape is the issue, if it’s to thick then try the inside.of an old floppy disk. There’s people that sell them on eBay or I could send you the remaining part of the one I used.

#8

As i said the camera is, as far as i can tell, good to go. It blocks all visible light and captures IR.

#9

Finally an update. After switching the resistors. LEDs and camera, (i ruined the first one when removing the IR filter), the system works. One problem is that when the LEDs are facing the camera, they get blown out. Only idea i have is to cover their center with something. Yaw works just fine, pitch is basically all the way down or up.

#10

Sand the LED’s slightly, make them glow more like a lamp than shine like a bulb.

#11

JayC is spot in there. Some bulbs can be sanded down (very gently) so that the light shines through the corners.
It might be possible to purchase bulbs of a different shape? I recall reading about sanding but never considered the bulb shape. I just got lucky

#12

Thank you for all the tips and help. Before committing to sanding the LEDs i tried covering their front with an aluminium tape and they work flawlessly. All in all after making it as hard as possible for myself i have a fully working head tracking. The only thing left is to get used to it and star using it naturally.

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