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TVRV8S #1 20/02/2013 - 17h03

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Hi,

I am trying to build a serial 3 point system using a 5V USB or 6V power supply but, unable to find the SFH485P leds, I bought the following HIRL5040 from RS Components here in the UK which seemed to offer a wide viewing angle and high power output.

http://uk.rs-online.com/web/p/ir-leds/2678403/

Here are the specs:

http://www.uv.es/~esanchis/cef/Caracteristicas/HIRL5040.pdf

I cannot work out what the supply voltage for the LED is - is it the forward voltage 1.7V?

I plugged the numbers (Vs = 6, Vf = 1.7, Imax = 100) which I *think* are correct for my LEDs into the site below and the resistor it told me to get was 43 Ohm, which is rather more than the 6.8 shown in the SFH485P sticky thread. Is this right?

http://www.daycounter.com/Calculators/LED-Tutorial-Calculator.phtml

Any help much appreciated.
Stormrider #2 20/02/2013 - 18h33

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Hi TVRV8S,
I found this for you
http://www.conrad-uk.com/ce/en/Search.html;jsessionid=DBF0EF80913177C22B1AF22EA2525452.ASTPCEN24?search=ir+led&filterType=SFH+485+P&filterBrand=Osram+Components

In the review on that site you can reed he uses them for a flightsim.

These SFH+485P, I use with a 10 ohm resistor and usb-powersource.I can see them very good in freetrack and everything works flawless.But..................I think that it also depends on what filter you use to block the normal light and which cam you  use.
When I started with freetrack I bought resistors with different values for experimenting.I started with 30 ohm and ended up with 10 ohm.
Did you know that you can't see ir-leds lighting up with you eyes?You can check them with a (web)camera or with your telephone.

If you stay with those other leds, I think I should do the same. Order a few resistors of different values ( 6 ohm up to 43 ohm)
and probable you will end-up using  one of 10 ohm.
I hope this helps you a little.

greetz Stormrider
Edited by Stormrider on 20/02/2013 at 18h36.
TVRV8S #3 21/02/2013 - 10h59

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Hi,

Thanks for your feedback.

I am going to stick with the LEDs I have as I have wired it all up. I just need to figure out what resistor I need for a 5V USB power supply.

Can anyone help with that?

I'd rather get it right rather than just put one in and hope for the best. My main problem is that I can't work out what the supply voltage is supposed to be for the HIRL5040.

Is it the forward voltage of 1.7V?

Thanks.
Steph #4 21/02/2013 - 15h05

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In theorie:

Serial circuit:

R = ( 5V – 3 x 1.7V) / 0.08A      (100mA is max. I take 80mA)

R = You do not need one (or get a 1 Ohm to protect your circuit.)

Or parallel circuit:

R = (5V - 1.7V) / 0.08A

R = 41.25 Ohm

You need 3 x 43 Ohm (1/4W min.)
TVRV8S #5 25/02/2013 - 14h24

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Steph,

At your suggestion that I did not need a resistor, I plugged in the 3 leds that have been wired up and they became VERY hot.

I note the forward voltage of the LEDs in their spec is TYPICAL 1.45V with MAX 1.7V, so I guess I do need a resistor after all.

I have found a place in the UK called bitsbox.co.uk that can send out small quantities of parts at a decent delivery price. Farnell, RS and others have extortionate delivery costs unless you're buying lots of stuff.

I have ordered some 6.8 and 10 ohm resistors.
Steph #6 25/02/2013 - 16h41

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At your suggestion that I did not need a resistor, I plugged in the 3 leds that have been wired up and they became VERY hot.



In serie or parallel?

The best way is to measure current flow, but if you add a 6.8 Ohm resistor (in serial circuit) it will be ok.

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