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FreeTrack Forum > FreeTrack : English Forum > Support : Tracking System > 20mA 3V LEDs and non-modded cam

RSS > 20mA 3V LEDs and non-modded cam, pls help a newbie who read the forums

sherab	#1 13/09/2008 - 02h04 Top
Class : Apprenti Posts : 5 Registered on : 13/09/2008 Off line	Hi guys. I did read the forums for the past two hours, but I am still quite ignorant on the subject. With three 20mA, 3V LEDs, and a camera that has not been modified (I would rather not modify it for now), what should my circuit look like? What battery should I use? What should be the total voltage? Is there any way I can avoid putting in a resistor? I would be very grateful if anyone could help. I discovered FT half a year ago, but I set it aside because I didn't know exactly how to exactly power the LEDs. Now the time has come, but I need some assistence, please. Thanks. Antonio
tristan68	#2 13/09/2008 - 07h53 Top
Class : Electronicien en chef Posts : 651 Registered on : 10/07/2007 Off line	Hello sherab 20mA, 3V LEDs An unusual value Are these IR leds ? red leds ? white leds ? Do you know their model ? what should my circuit look like? What battery should I use? That doesn't work this way. Usually, you have a battery, or power adapter, and we calculate the setup schematics and resistor value to make it work. Hint : if your leds are really 3v model, you'll need at least a 3.5v power supply or a battery pack able to provide more than 3.5v (usually a 3 cells or 4 cells battery pack). Is there any way I can avoid putting in a resistor? DEFINITELY NOT As already stated several time in this forum, leds are not light bulbs. Trying to use leds directly on a power source WILL overstress them and result in leds dying after a short time of use or leds frying instantly when you connect your setup, depending of the leds and your power source. A CURRENT LIMITING DEVICE (USUALLY RESISTOR(S) ) IS MANDATORY WHEN YOU WORK WITH LEDS. furthermore, resistors are cheap, simple adn common components. So using a resistor really shouldn't be an issue. So please could you : - confirm the led model or the led characteristics - tell us what kind of power source you plan to use so we can help you with the setup . cya
sherab	#3 13/09/2008 - 10h19 Top
Class : Apprenti Posts : 5 Registered on : 13/09/2008 Off line	Tristan, Thanks for your excellent reply. Illuminating. Now I understand some aspects better. Apologies. I know how it feels to read thru noobs questions when one knows the subject, at least for me ! I can confirm the LED specs (20mA, 3v). But I will go now to the only nearby shop and look for a lesser voltage LED. Will report later
sherab	#4 13/09/2008 - 10h30 Top
Class : Apprenti Posts : 5 Registered on : 13/09/2008 Off line	In the shop near here, the smaller voltage LED they have is 1.8V, next one up is 2.3V, then my 3V.
tristan68	#5 13/09/2008 - 11h51 Top
Class : Electronicien en chef Posts : 651 Registered on : 10/07/2007 Off line	hello sherab no need to change the leds, it was only unusual not false. Can you tell me what power supply you intent to use , so i can help you with the setup ? cya
sherab	#6 13/09/2008 - 13h00 Top
Class : Apprenti Posts : 5 Registered on : 13/09/2008 Off line	I just found a charger for an old phone that died. It provides 3.7 volts. Is it suitable for the job? Using the calc wizard on the website: 3.7V unregulated power supply, 3 LED cap, 1.8V LED, 20mA (I bought these too now), I get a resistor value of 150ohms. Now, (here you're gonna laugh) should I use one resistor for each LED (3 resistors total) or one for all? (You see the level I'm on!) Alternatively, I can use batteries, any type you tell me, ideally rechargeable but I see non rechargeable are preferred.
tristan68	#7 13/09/2008 - 17h43 Top
Class : Electronicien en chef Posts : 651 Registered on : 10/07/2007 Off line	Hello sherab. 150 ohms is the good value , according to your specs. About the number of resistors, the wizard should have also told you about this. For your setup, it suggested a parallel setup, thats 3 resistors then. In a parallel setup , you need to use a resistor for each led. About your wish to use batteries, you can use rechargeable batteries if you want to, it causes no problem. just remember rechargeable batteries only provide 1.2v output voltage per cell. cya
sherab	#8 14/09/2008 - 12h25 Top
Class : Apprenti Posts : 5 Registered on : 13/09/2008 Off line	Hey Tristan. If I use the following config, the wizard tells me I should use 125.5 ohms resistors. I have 120 ohms resistors. Is the margin acceptable? Power supply 3.7V LED 2.3V 20mA
tristan68	#9 15/09/2008 - 09h03 Top
Class : Electronicien en chef Posts : 651 Registered on : 10/07/2007 Off line	hello sherab I usually prefer to go the other way (using the next value in the resistors range , rather than the previous) but yes , the margin is still acceptable. btw : Didn't you say in your previous post you were using 1.8v leds ? cya

FreeTrack Forum > FreeTrack : English Forum > Support : Tracking System > 20mA 3V LEDs and non-modded cam

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