IR led carrier wave

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Hey All

Can some one explain what is a carrier wave and how i use it,i want to transmit data using a ir led (for a long range some thing like 4-5 meters or more if possible)

and how can i use it with my avr?

(sorry for my English :) )

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OK thx for the info
but it don't explain what is a carrier wave and how I use it?

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Is this a homework question? I didn't read all one million links on google for 'carrier wave', but the first two looked pretty clear.

Imagecraft compiler user

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Its not a homework question...
and i read the first 4-5 links on Google :)
The thing is i cant understand how i can create a carrier wave using avr(or some other circuit)and how i decode it???

Its look like a total newbie's question :lol:

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well what kind of carrier wave?

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A 'carrier wave' is just a 'beep' or 'tone' of sound, light, or radio waves. A steady signal. For it to 'carry' some information, it must be modulated in amplitude or frequency. Multiplication of the carrier signal times the modulation signal will impose the modulating signal on the carrier. An example is morse code... the carrier is a continuous wave tone of rf at 6mhz. The brass key is the modulating signal. When the key is open, you multiply the carrier amplitude times 0. When the key is pressed, you multiply by 1. This is called on-off keying.

Imagecraft compiler user

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for IR on-off keying ins used, meaning that one state is sent by transmitting the carrier wave, the other state is transmitted by the lack of the carrier wave. Note I said state and not bit, that is because depending on the protocol, a bit is transmitted by using one or both states of varying duration, or sequence.

For IR to create the carrier you simply blink the LED on and off at the desired frequency.

Writing code is like having sex.... make one little mistake, and you're supporting it for life.

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Carrier wave in the context of an IR source can lead to confusion.

Normally, a carrier is a signal (usually electromagnetic, but sometimes on wire or cable) that is modulated by the information being transmitted. You can turn the carrier on and off (sometimes called OOK, or on-off keying) for which Morse Code is an example, but data can be used, also. You can vary the amplitude (amplitude modulation, or AM, commonly used for medium and short wave broadcasting). You can vary the frequency (FM). All of these can also be used for data.

Now, when you get to a light source (which infrared really is), the light IS the carrier. It is very hard to frequency modulate it, so amplitude, especially OOK, is usually the choice.

But, it does not stop there. You can superimpose one carrier on another (use one to modulate the other). Thus, you COULD modulate the IR source at a high rate (say, on and off and some 1,000 to 1,000,000 times a second); this would be a subcarrier. Then modulate various properties of THAT subcarrier (key it on and off, vary its frequency, etc).

Such a carrier could be easily generated directly by a microprocessor.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Here's a project that should be a good example on IR and carrier frequencies:

http://thebloughs.net/hobbies/el...

Cheers,

Tom

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The only reson to use a carrier for a IR system
(normaly about 40KHz) is so the receiver can AC couple
the input, so it can see if the tone is there or not.
You need to do this because the IR ligth isn't constand , sunshine, ligth bulb flame etc.
But all of those change slowly.
To round up: even if you use OOK you actually look
for 40KHz or nothing

Jens

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AVR based generic infrared transceiver http://www.embedds.com/avr-based-generic-infrared-transceiver/ might be worth a look at.

[edit] the actual project is at http://www.lochraster.org/unzap/
Theory etc is at http://www.sbprojects.com/knowledge/ir/ir.htm[/edit]

C. H.
-------------------------------------------------------------------
It's only waste if you don't use it!

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BIG thx to every one that helped me!!!
I will post my small project later(when the project will be ready ):)