FreeTrack Forum

I went to:

http://www.free-track.net/english/hardware/calcled/

And

http://www.free-track.net/fichiers/support.pdf

And entered the following values.

I have a regulated DC power supply 5 volts, 300mA from Digikey
I have 3 SFH485P  (880nm 5mm flat led).  1.5 forward voltage, 100mA forward current.

I am entering the values for EACH individual part, corrrect?  (i.e., I'm not entering 4.5V forward voltage and and 300mA forward current for all 3 LED's... correct?)

When I used the only calculator, I got a drawing with the led's and resitor in series...with the resistor value of 5ohms (current of 98mA, disp. power of .05 Watts).

When I used the calculator in the support.pdf document, I got a drawing with the led's and resistors in parallel with the resistor value of 35ohms.

I don't understand the difference.  Are both acceptable or is one better than the other?

Thanks

Ted

Hello trwagner1


to make things simple :

- the led calc in the PDF document is older, and was made when we hadn't tought about all possible settings. It shouldn't be used anymore since the website calculator is available.

- you plan to drive your SFH485P at 100mA. This is too much. There are several threads talking about this but i'd recommend the following values :

If you webcam is IR modded, use 25mA  to 50mA (25mA is enough in most cases)
If your webcam isn't IR modded, use 50mA to 75mA.

Don't drive your leds at more than 75mA , it would overstress them.

cya

Ah!  ok, so, then, I just plug in 25mA in the calculator and voila, shows me what I need to use as far as a resistor goes, correct?  Which, gives me a resitor of 20 Ohms.

Ted

Correct  

Enjoy your setup.

cya

- you plan to drive your SFH485P at 100mA. This is too much. There are several threads talking about this but i'd recommend the following values :

If you webcam is IR modded, use 25mA  to 50mA (25mA is enough in most cases)
If your webcam isn't IR modded, use 50mA to 75mA.

Hardware-FAQ says:

My LED's specification says it's forward current is 100mA. So that's what i should input in the LED Assembly wizard?
This value is LEDs maximum rating, meaning that it's the maximum current that won't damage the LED. Anything higher may cause permanent damage.
Here are some example recommendations for current values for IR LEDs depending on webcam:

     visible light filter - about 25% of maximum rating. (SFH485P : 25 mA)
     * stock camera (with IR filter present) and visible light filter applied - about 50%-70% of maximum rating (only use the higher value if the lower isn't too bright). (SFH485P : 50-70 mA)
     * illumination for reflective tracking (the camera has to be fully IR-modified: ni IR filter and added visible light filter) - 90%-100% of maximum value. When using such high values it's the best to mount LED in a PCB for better heat dissipation. (SFH485P : 90-100 mA)

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