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FreeTrack Forum > FreeTrack : English Forum > Support : Tracking System > point model - problems with resistor and LED's

RSS > point model - problems with resistor and LED's, powering with USB cable ..

RedLine	#1 09/12/2010 - 19h54 Top
Class : Apprenti Posts : 8 Registered on : 09/12/2010 Off line	Hi, im new here and i have my first problem with setting up my point model .. i buyed the IR LED's as follows: Vf = 1.5v 65mA i will use usb power to feed the led's.. V = 5v (actually 4,98v) i wanted to use 3 led's and give each of them a resistor so i made the calculations for 1 LED and it came out that i need a 62Ohm resistor i buyed a 65Ohms resistor and soldered 1 pin to the positive (+) pole of the usb cable and the other pin to the positive (+) pole of the led .. i soldered the negative (-) pole of the USB cable direct to the negative (-) pin of the led ... it does not work and if i test the voltage on the led's pin i actuallyget 4.98v (same as without resistor) .. why??????!?!?!?!?!?!?! i tested different resistors (of the same class and type ... 65Ohm) and they all give me 4.98v .. what do i do wrong?? thanks for the help ..
flyforever	#2 09/12/2010 - 21h08 Top
Class : Apprenti Posts : 10 Registered on : 09/11/2010 Off line	Ir LEDs have their polarity reversed. Negative is positive and positive is negative.
dewey1	#3 09/12/2010 - 22h03 Top
Class : Habitué Posts : 191 Registered on : 25/06/2010 Off line	flyforever @ 09/12/2010 - 21h08 a dit: Ir LEDs have their polarity reversed. Negative is positive and positive is negative. That statement is absolutely meaning less. The correct method for LEDs whether IR or not, is to look closely for a flat on the side of the LED. Do not go by lead length as some due. The flat side is the cathode which is the negative (-) side. To the original poster, see post #112 for a good pictorial of wiring in this link: http://forum.free-track.net/index.php?showtopic=1856&page=8 See this for cathode or minus of LED: Edited by dewey1 on 09/12/2010 at 22h05.
RedLine	#4 09/12/2010 - 23h17 Top
Class : Apprenti Posts : 8 Registered on : 09/12/2010 Off line	dewey1 @ 09/12/2010 - 22h03 a dit: flyforever @ 09/12/2010 - 21h08 a dit: Ir LEDs have their polarity reversed. Negative is positive and positive is negative. That statement is absolutely meaning less. The correct method for LEDs whether IR or not, is to look closely for a flat on the side of the LED. Do not go by lead length as some due. The flat side is the cathode which is the negative (-) side. To the original poster, see post #112 for a good pictorial of wiring in this link: http://forum.free-track.net/index.php?showtopic=1856&page=8 See this for cathode or minus of LED: hi! thanks for the fast answer .. i knew which lead is wich pole before and i soldered it up right i think (with the statement "the flat side of the led" you mean the bigger inner flat part of the led wich holds the reflector cup is that right?) my problem is that either the resistor is the wrong one or it is foulty (all 3 that i tested ?!?!?!?!) the LED's are working good (i tryed them with normal 1.5v batteries and they light up in freetrack) but something is wrong with the resistor and the voltage .. i get 4,98v from my motherboard usb port and when i solder the positive pole to the resistor and measure the tension on the other lead of the resistor and the gnd cable i get 4,98v too .. so there must be something wrong .. i made the calculation on the freetrack site and calculated for 1 LED as i wanted to use 3 resistors (one per LED) and came out i need 62Ohm .. 62Ohm wasn't in stock and so i get 65Ohm .. but they actualy do not lower the tension of 5v .. am i using the wrong resistors? are my calculations right? thanks! (is it right that i should get 1,5v at the leads of the LED whan the right resistor is installed? why does mine do not lower the voltage?)
RedLine	#5 09/12/2010 - 23h46 Top
Class : Apprenti Posts : 8 Registered on : 09/12/2010 Off line	since i'm getting nowhere i actually tried to reverse the poles (even if i were sure that i was right because on all the diagrams on the web i found the same statement of how to find the correct poles of a IR led) and now it works! i have negative where normaly positive would be (the smaller part in the led) and for some reason i am now getting 1,4v on the led's and not 4,98 like before .. it's ok now!
Gr3mlin	#6 12/12/2010 - 20h54 Top
Class : Apprenti Posts : 5 Registered on : 12/12/2010 Off line	thats correct, you will get 4.98vdc due to there being no load. as soon as a load is introduced the voltage will drop.
Matthewop	#7 21/12/2010 - 09h56 Top
Class : Apprenti Posts : 9 Registered on : 13/10/2010 Off line	so i am wrong before. e..i did't know it before!! True Blood Season 3 DVD \| The Glades Season 1 DVD Boxset

FreeTrack Forum > FreeTrack : English Forum > Support : Tracking System > point model - problems with resistor and LED's

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