Society of Robots - Robot Forum
Electronics => Electronics => Topic started by: andd64 on June 09, 2009, 04:42:17 PM
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This maybe a stupid question, but what's the difference between an IR emitter and IR led? I'm making a multi-touch screen, and i need a bunch of IR leds, but i heard of this IR emitter that's much much cheaper http://www.newark.com/vishay-semiconductor/vsmg3700-gs08/ir-emitter/dp/31M2973?_requestid=250017 (http://www.newark.com/vishay-semiconductor/vsmg3700-gs08/ir-emitter/dp/31M2973?_requestid=250017).
Does anyone have a good place to buy cheap IR leds from? Lets say about 100 of them. Digikey and dealextreme are two I'm thinking of using right now.
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Hi,
This maybe a stupid question, but what's the difference between an IR emitter and IR led?
The spelling.
LED (all caps, as it's an acronym) means Light Emitting Diode.
Does anyone have a good place to buy cheap IR leds from? Lets say about 100 of them. Digikey and dealextreme are two I'm thinking of using right now.
What wavelength and what angle of half intensity do you need?
eg. 60 Degree IR-LEDs
850nm = $45 for 100 LEDs
940nm = $9 for 100 LEDs
Sometimes it's cheaper to use a (few) more powerfull LEDs, but I guess that won't work in your application (too bad, since you can have a 20W IR-LED :))
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Hey Soeren,
Wavelength can be 780-940 nm, angle about 48 deg, less than 60 deg, intensity minimum 80 mw. The link i posted for the emitter looked different than the IR led's though?
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To be able to use an IR led effectively it needs to be modulated.
That is it needs to be turned on and off at a certain frequency.
Do not confuse this with the frequency of IR this is the frequency of turning
the LED on and off just like you would do with a normal light LED.
The reason for this is that the receiver can then have a filter that
would not accept except the frequency of the Emmitter so that it will
be able to avoid normal IR that comes from lamps and sunlight etc.
So with this setup the Receiver and Emmitter would have a correspondance
that would make the receiver sure that when it receives the on and off
the emmitter is giving it will respond with assurance that it is a real signal.
an LED just transmits a (when it is on) a continusous signal and thus
if there is some other source like the sun or a bright lamp then a receiver
that just looks for IR light might be confused and thus will respond incorrectly.
But strictly speeking an IR LED is also an emmitter, but I think this is difference
that some people may use to distinguis between an unmodulated IR LED and
a modulated one.
Sam
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The link i posted for the emitter looked different than the IR led's though?
They are still IR LED's just in a different package casing. The ones in that link are designed to fit flush to a surface. Sometimes applications dont need standard dome type led's so others are available. You can also get tri color leds with the same package casing.
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Hi,
To be able to use an IR led effectively it needs to be modulated.
That is it needs to be turned on and off at a certain frequency.
Do not confuse this with the frequency of IR this is the frequency of turning
the LED on and off just like you would do with a normal light LED.
The reason for this is that the receiver can then have a filter that
would not accept except the frequency of the Emmitter so that it will
be able to avoid normal IR that comes from lamps and sunlight etc.
So with this setup the Receiver and Emmitter would have a correspondance
that would make the receiver sure that when it receives the on and off
the emmitter is giving it will respond with assurance that it is a real signal.
It is said, that to the one who's only got a hammer, every problem looks like a nail.
IR is used in so many apps and while some of them (mainly remote control and the like) use a carrier wave, other apps would only be worsened by the carrier.
Not every app use an integrated demodulating remote control receiver !
But strictly speeking an IR LED is also an emmitter, but I think this is difference
that some people may use to distinguis between an unmodulated IR LED and
a modulated one.
Not only strictly speaking, but speaking in every which way (but nonsense), LED means Light Emitting Diode as I wrote. This is not a case of "some people" inventing their own terms, but simply that the term emitter is sometimes used alone to distinguish it from a receiver, when the subject is allready known to be about LEDs and photo diodes.
Modulated vs. unmodulated (i.e. carrier wave or not) has nothing to do with it being an emitter.
Now I'm running out of ways to drive the point through, so please read it twice, if it still gives you any doubts, or look up the word "emit" in a thesaurus.
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Basically :)
IR emmiter is something that emits infrared :) for example - a heater is an infrared emmiter, and your body is also infrared emmiter
IR LED is a piece of semiconductor covered with plastic that emmits infrared wave with predefined parameters (wave length, width of beam, power)
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Hi,
IR emmiter is something that emits infrared :) for example - a heater is an infrared emmiter [...]
It might have escaped you, but if you read the original post, you should have seen that we're not talking heaters, clothes irons, live mammals, the sun or whatever, but the specific "emitter" (one "m" and two "t"s) shown in the link: http://www.newark.com/vishay-semiconductor/vsmg3700-gs08/ir-emitter/dp/31M2973?_requestid=250017 (http://www.newark.com/vishay-semiconductor/vsmg3700-gs08/ir-emitter/dp/31M2973?_requestid=250017)