FreeTrack Forum

So I'm looking to build a three point cap, but I don't know the first thing about electronics, which, needless to say, is a hindrance.

I was looking to buy these LEDs

http://www.westfloridacomponents.com/mm5/merchant.mvc?Screen=PROD&Product_Code=LED028&Category_Code=InfraredLEDs&Store_Code=wfc

With this AD/DC adapter, or one like it.

http://cgi.ebay.com/A-C-to-D-C-Plug-in-Adapter-DC-6V-300-mA_W0QQitemZ310053062423QQcmdZViewItem

So I have a couple of questions.

1. What kind of resistor, if any, would I need for the above set up? I tried the LED Wizard but I was more confused than when I started.

2. If I swapped out the above AD/DC adapter for one that is 4.8V at 250 mA, would that be enough power, if yes, would it need a resistor, if yes, what kind?


Thank you for your help in advance.

Hello Leokian, and welcome aboard  


About the leds :

They're 940 nm leds, so they'll be difficult to see for some webcams , without IR modding the webcam.
If you can find 880 nm IR leds , thats a better choice.

40° viewing angle is a bit narrow for freetrack, but you can easily widen this angle by filing the leds, so thats ok.

The max current for these leds is 100 mA, but you only seldom need to operate the leds at max current.

I usually suggest operating at half power, thats more than enough for most of the cases.

So we have :

Led forward voltage : about 1.3v (at 50mA)
led forward current : 50 mA

About the power adapter :

Its a 6v 300mA unregulated power supply
Its ok for use with freetrack.


Resistor calculation :


So we have :

setup : 3 points cap
power supply type : unregulated
power supply voltage : 6v
led forward voltage : 1.3v
led forward current : 50mA

If you use the wizard with those values, you'll get :

Assembly mode : serial assembly
You'll need 3 leds and 1 resistor

The resistor value is 82 ohms

The resistor wil have to sustain a power dissipation of about 0.19W, so you can use either a 1/2W or 1W resistor.
(Don't go for a 1/4w resistor, max power is a bit too close to the 0.19W, better go the safe way, and resistors are very cheap components, so its ok).


Resistor model : ie : 82 ohms 5% 1/2w carbon resistor.


hope this helps

cya
.

Ok, thank you.

A couple more questions.

How do I regulate how much power gets to the LEDs, as in, how do I run it at a certain amount of mAs?

Will the LEDs running at 940 nm be a moot point if I remove the IR filter on the camera?

If I file down the LEDs, would I have to give them a matte finish?

Hello Leokian

How do I regulate how much power gets to the LEDs, as in, how do I run it at a certain amount of mAs?

Thats the job of the resistor. You choose the current, and then calculate the appropriate resistor.

The resistor depends of :
- your led characteristics
- the desired current
- your power supply characteristics
- the assembly type

The led wizard does this for you, so you don't have to bother with choices and formulas.

Will the LEDs running at 940 nm be a moot point if I remove the IR filter on the camera?

When working with 940nm leds, some webcams can see the IR light, other have to be IR modded to be able to perceive this kind of IR.

But once IR modded, EVERY webcam can track 940nm IR leds correctly.


So, if you're lucky, you won't even have to IR mod your webcam. But if you need to, your webcam will for sure track your leds correctly once modded.

If I file down the LEDs, would I have to give them a matte finish?

Just use fine sandpaper to finish the work.


cya

Thank you very much for your answers.

EDIT: Also, am I correct in thinking that "IR Modding" is pretty much just removing the IR filter?

yes, IR modding is just removing the IR Filter.