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FreeTrack Forum > FreeTrack : English Forum > Support : Tracking System > LED's powered off USB will not light

RSS >  LED's powered off USB will not light
mutti_wilson #1 29/12/2012 - 02h21

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Registered on : 15/08/2008

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I am using LED's from Radioshack the same as the post below. Same resistor, in a series etc.

Yes they will work.
The LEDS will probably need to have the lens sanded and polished to increase beam angle.

Series circuit with USB power:
1.28 x 3= 3.84
5.0-3.84=1.16
1.16/.05=23.2 Ohms for 50 mA

Use a 1/2W 5% resistor in the range of 20 Ohm to 22 Ohm.

20 Ohm will be 58 Ma current.
22 Ohm will be 53 Ma current.

You could use 10 Ohm resistors and series wire for 20 Ohm.

http://www.radioshack.com/product/index.jsp?productId=2062565

I cannot get them to light up. I have 5V at the power adapters (tried 2), everything ohms out, and I have a proper 22OHM measured resistance. I have checked and double checked the polarity on the LED's, and they are exact. Could an LED burn out and if so is there any sign of them doing so?

Thanks!
dewey1 #2 29/12/2012 - 03h30

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Registered on : 25/06/2010

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mutti_wilson @ 29/12/2012 - 02h21 a dit:


I cannot get them to light up. I have 5V at the power adapters (tried 2), everything ohms out, and I have a proper 22OHM measured resistance. I have checked and double checked the polarity on the LED's, and they are exact. Could an LED burn out and if so is there any sign of them doing so?

Thanks!



940nm IR LEDs will not be visible to the human eye.
You may need to use a camera to "see them".

If you have a voltmeter, check the voltage across each LED.
Edited by dewey1 on 29/12/2012 at 03h33.
mutti_wilson #3 30/12/2012 - 02h13

Class : Apprenti
Posts : 5
Registered on : 15/08/2008

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This is pretty funny. I wasn't even thinking about them being invisible. Once I checked with the camera I found them on. I got my profile worked out and it is working great. Thanks for the reply. I hope someone finds it useful!

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