FreeTrack Forum

So, i bought 3 infrared LED from radio shack (In the USA)
I was wondering if i can hook it up with 3 1.2v AA batteries without a resistor.

The specs for my LEDs are:
Radiant Powder Output (100ma) 16mW min.
Forward Voltage: 1.2V
Forward Current: 100mA
Wave Length: 940nm

If not, what resistor specs would i need to buy to fit my needs.
My battery source is either:
Rechargeable 1.2v AA batteries
or
Alkaline 1.5v AA batteries

Help please and also, i have a Logitech Quickcam express E1000, what do i need to modify to make it pick up my IR LED?
I dont think anyone else has the same webcam on here.

heyy welcome

if you go to:
http://www.free-track.net/english/hardware/calcled/

it should tell you the best setup for what ya using.

guessing the AA batteries will be in series, if so you add up the voltages for the power supply field.

so it will be 4v for the standard and 3.6v for rechargeable.

seeing as you might be using 1.2v i think you will want to go for a parallel set up as it will just be matching the combined forward voltage is the LED's were in series.

as for the resistance you will want to run the LED's at lower than their max current, so say 75mA or 50ma seems to be what people go for.

not if you are going to be changing between using normal and rechargeable batteries there's a little more thinking. work out the resistance for the largest voltage at the upper limit you want the LED's to be at

so say 4v@75mA you would need 3x39ohm resistors for normal batteries. but if you use rechargeable because of the resistors you will get a lower current going through when used. see what am saying?

as for the cam just do what i did, start up the program and have a fiddle about. from other posts can see what people did with settings, turn off auto exposure and setting the format and resolution. aiming to get steady 30fps and then tweaking the exposure and threshold till only the IR light is visible. i played about with a tv remote to get used to what i would need to change

good luck an hope i helped a bit

Thanks for  the help. That explains alot.
I still few question and i dont understand the results i got from the calculator.
So i should get 3x39ohm resistors if i use 3 regular batteries? Im guessing this is the non-parallel setup right?

If running on batteries you want to keep the current as low as possible to avoid having to keep replacing or re-charging the batteries. I connect my IR leds in series. The advantage of a series wired LED set up is that the current consumption is three times less than if they were connected in parallel.

Here in the UK you can buy LED Clip sockets with each LED socket having around 10cm of colour coded wire (Rapid Electronics). No need to solder the leds - just plug them in!  10cm of wire on each socket is more than enough for most Track clip designs.   I also run my IR LEDs at around 75 ma and use the USB to power them but a single in line resistor of around 10 ohms is usually fine for most and is all that you need to keep the batteries fresher for longer. With your LED's you could omit the resistor altogether given that they are 1.2V.  Connect them in series and power them from 3.6V battery pack.  The 3.6V will divide across each LED at around 1.2V per LED.   However, some LED's have a nasty habit of 'current hogging' and will appear brighter in your FT tracking screen - adding a low value resistor from either the positive or negative connection of the battery pack helps to prevent this. (doesn't matter which of the battery leads you put the resistor in - it still limits the current).

The only disadvantage of series wired leds is that if one fails you wont know which one it is as all will stop working.  Use a non IR LED's and plug it into each socket untill the culprit has been located and then remove the non IR LED and fit an IR replacement. Always best to order a few spare LEDS so that you have them if needed.

Do a search for LED clip holders or LED Sockets and see if any come up!

Hello,

I live in Canada and I'm having some difficult finding OSRAM IR LED.  I found something that looks equivalent.  But I wanted to confirm with the experts first.

http://parts.digikey.ca/1/1/22611-ir-led-950nm-17-deg-side-view-ln54.html this is what I found

I also wanted to verify if a 30% view angle is bad for freetrack vs the 80% view angle.  Sounds intuitive but I just want to confirm.

Edit:  Actually I found this item http://ca.digikey.com/1/1/211477-ir-led-940nm-80-deg-side-view-lna2603f.html and I'm wondering if this would be a sufficient replace for the recommended OSAM ones?

Thanks everyone

Type in 475-1470-ND in your DigiKey Canada search.
That is their part number for the Osram SH485P.

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=475-1470-ND

Digikey is located in Thief River Falls Minnesota. Fairly close to the Canadian border.

Thanks dewey1