FreeTrack Forum

Hi,

Thanks for the great programme. I haven't tried it yet but it seems really really great!

I plan to use the SFH485P LEDs as stated on this website. The ratings for these LEDs are as follows:

   * IR EMITTER, 5MM 880NM
   * Wavelength, typ:880nm
   * Current, forward If:100mA
   * Angle, viewing:160°
   * Case style:Radial
   * Angle, full:160°
   * Angle, half:80°
   * Current, If av:100mA
   * LED / lamp size:5mm/T1.3/4
   * Pitch:2.54mm
   * Radiant intensity:48mW/Sr
   * Radiant intensity, max:6.3mW/Sr
   * Radiant intensity, min:3.15mW/Sr
   * Time, t off:0.5µs
   * Time, t on:0.6µs
   * Voltage, Vf typ:3V
   * Wavelength, peak:880nm
   * Colour, LED:Infra red

These stats are taken directly from the Finnish Farnell website where I plan to buy these LEDs.

I was wondering since the Voltage is 3V is it safe to assume that I do not need any resistors if I use a 3 Volt battery (1,5volts x 2)?

Also if I use 2 x 1,5 volts batteries then I guess the batteries should be behind each other (in series) in the circuit and not in parallel?

BFC

Hello Bluefightingcat

1) Farnell has a known error in its database :

the SFH485P has a forward voltage of 1.5V , not 3V

2) It's NEVER safe to operate leds without current limiting system, eg resistors.

So , ALWAYS use resistors

3) Don't exceed 70mA operating current when using SFH485P, the 100mA max is given only in a specific use (PCB mounted).

4)

I guess the batteries should be behind each other (in series)

Yes. serial wiring, to get a 3V equivalent battery.

5) for resistor choice, use the wizard with the following values :

power supply : 3V
power supply type : batteries
led forward voltage : 1.5V
led forward current : your need (between 20mA and 70mA)

cya

Hi,

Thanks for the answer!!

One other question. I am going to try and build a 3-point system. I was looking at the manual and at the photos and I am a little confused about the setup. Should the 3 LEDs be in a upside down T shape or should they be in a line on the same plane? (compared to the 4 point system which LED would I remove?)

Also on the website it says:

As an infra-red filter, a good tip is to use two or three dark photograph negatives (or better, not exposed) superimposed and installed in front of the cam lens.

So its ok to use unexposed film? So I just need to buy normal camera film and then rip out the film and use that??

BFC

bluefightingcat @ 21/01/2008 - 11h58 a dit:

Should the 3 LEDs be in a upside down T shape or should they be in a line on the same plane?

The cap model is an inverted T shape and the clip model is a flat plane.
Check the software to get an idea of each tracking mode and the associated model.

(compared to the 4 point system which LED would I remove?)

The front middle LED.

So its ok to use unexposed film? So I just need to buy normal camera film and then rip out the film and use that??

No, the film needs to be developed, but doesn't have to be exposed however it is a MUCH better filter when it's been exposed. For best results take a photo of a fluorescent light for about 5 seconds with the camera's aperture fully open so that the frame is completely over-exposed.

Hi,

Thanks for the answers. Which setup up (cap or clip) would you recommend for FSX? Or is it just a matter of personal preference?

Also regarding the filter. Would it not be enough to buy a film, rip out the film from the roll hold it in front of a light for a while and then send it to be developed. (The reason I am asking is that I don't have access to a film camera. All my cameras are digital).

BFC

bluefightingcat @ 21/01/2008 - 12h57 a dit:

Which setup up (cap or clip) would you recommend for FSX? Or is it just a matter of personal preference?

The clip is for headphone users. It doesn't have a NAN bug and allows for some parasitic translation reduction.

Also regarding the filter. Would it not be enough to buy a film, rip out the film from the roll hold it in front of a light for a while and then send it to be developed.

Just pull the film out under a fluorescent light, expose it for 5 seconds then put it into a dark container like a black garbage bag and reel the film back into its case. When getting it developed don't forget to mention that you don't want any prints. :P