FreeTrack Forum

I purchased 8 of the SPH485P IR LEDs, and a 6 VDC switched battery pack (4x1.5V AA). And I wired the LEDs exactly as shown, in series. NOw, this is a 6 VDC supply instead of 5 (USB) and I used 11 ohms (3x33 ohm in parallel).

The LEDs do not have enough current to light. I proved that each one was working by putting the leads of my ohmmeter (set to the Rx1 scale) on the leads, and could see the glow on my camera (incidentally, the Microsoft HD5000 camera works very well without any modification, and with a piece of floppy disc as a lens filter - I'll add that to the camera thread). The ohmmeter provides 1.5 VDC, buffered by in internal resistor, so the LED lit at about 1/2 brightness, but still very noticeable on the camera.

So I know that all of the LEDs are good and will produce IR light with a 1.5 VDC source. Still, 3 of them in series with an 11 ohm resistor with a 6 VDC supply will not drive them. These things have a 5 volt reverse voltage and 100 ma forward current. So what's wrong with the schematics posted up here? They don't work for me, so I must be missing something.

I even tried the set-up using the USB power (5VDC through a USB cable and a plug-in adapter) and it still doesn't work.

Check the current with your multimeter.
Check without the floppy filter, (this filter is a bad solution because it blocks part of ir-light too.)

I feel more than a little embarrassed to admit what was wrong. As I stated, the ohmmeter did manage to turn on one of the LEDs, so I knew the LEDs were good. But I decided to try a simple test of putting one LED across a 1.5 volt AA battery (if the ohmmeter worked, a battery should do just as good, if not better), so I took the + lead on the LED and held it to the + end of the battery and touched the - wire to the - end. Nothing!

Cmon! It worked with the ohmmeter, so I did THAT test again, and it lit. Back to the AA cell. Again, nothing. I was mad, so I decided to reverse the leads...what could it hurt, and I have 8 of them to play with.

It lit up like a Christmas tree! I went back and set up the original circuit, with 3 LEDs in a series circuit with a 33 ohm resistor, and connected it up to my 6 volt battery pack - backwards/reverse polarity (I thought)! All 3 lit up very nicely!

I went back and looked at the datasheet for the SFH485P LED, and it shows the longer of the 2 leads (flat side) as being the anode ( - lead), and I just went with the common idea of it being the cathode (+).  After wracking my 66-year-old brain for 3 days, I feel really foolish, but also glad that now I can proceed with making the mount. Now I need to figure out whether the 3-LED cap model, or the 3-LED vertical clip mount, is the better device.

Any input on that one?

I went back and looked at the datasheet for the SFH485P LED, and it shows the longer of the 2 leads (flat side) as being the anode ( - lead), and I just went with the common idea of it being the cathode (+).

...you're not the first. I always check the inside of LEDs for cathode and anode as you cannot rely on the leads.

Hoi Gary,
as an answer to your question what will be the best, a capmodel or a clipmodel.I got the best results with a three point capmodel. The three point capmodel  was easy to make and easy to configurate.
I use a Travel charger batterypack with usb output  as a powersupply, 10 ohm resistor and it works great.
With this setup  I can choose if I want to use a headphone or not.When it is mounted on your headphone you always have to use it.Most of the time it is more fun to hear it from the speakers.