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Modulation for infrared headphone circuit

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marcoamir

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our project is infraredheadfone
we tried to send directly the audio signal, but actually we have a problem that IR LED and detctor should face each other ( it gives a distance o arround 1 meter but the MUST FACE EACH OTHER DIRCTLY)
note we are using te detetor thatlooks like a LED ( black one and have 2 legs)

So we knew that we have another detector ( have 3 leg , and X shape ), but we knew that it'sworking on 38KHz range which is above audio range............so we must have a modulation


so noww what modltion souldwe use, we need advices and CIRCUITS, we hav no time .. project delivery in 2 days please heeelp
 

Infared headfone

The detector which requires modulation is no use for your application. Your original circuit needs more receiver gain and/or more LED power. You didn't say how you were modulating. FM on a carrier would be my suggestion.

2 days isn't long enough to design & build a decent circuit.

Keith
 

Re: Infared headfone

keith1200rs said:
The detector which requires modulation is no use for your application. Your original circuit needs more receiver gain and/or more LED power. You didn't say how you were modulating. FM on a carrier would be my suggestion.

2 days isn't long enough to design & build a decent circuit.

Keith

thx for replying
but
1- i dont understanded : ""]The detector which requires modulation is no use for your application."
2- how to make FM modultion can u help me with a design
 

Infared headfone

It would be useful to see a circuit of what you have built that works. The best chance of doing something quickly would be to modify it with more gain.

Keith
 

Re: Infared headfone

What keith1200rs is telling you is that IR detectors for remote control are of no use. There are two reasons:
1. They normally have built in 38KHz carrier filters to make them insensitive to all but remote control transmitters.
2. A 38KHz carrier is too low in frequency to carry useful quality audio. If you are sending 8-bit data (remember they have digital outputs so you can't use analog) the byte rate cannot exceed 4750 bytes per second and Nyquist's theorems tell us the highest modulation frequency would be 2.375KHz. That would be less than telephone line quality and monophonic.

Your options are higher power IR LEDs, the ones with a deep red visible glow are used commercially for IR communication either using analog modulation or an FM carrier. Bear in mind that analog modulation (AM) will make your receiver susceptible to input from fluorescent lights and other 'flickering' sources.

Brian.
 

Infared headfone

Brian,

Thanks for the explanation - my thumbs get tired after a few dozen words!

The common filter IR detectors are limited to 2400 baud I think.

Keith
 

Re: Infared headfone

Actually, I typed the reply and tried to send it only to find Edaboard had gone off line for a couple of hours.:x I think there's a weekly down-time for maintenance so I had to copy and save it to a file so I could upload it later. I too have 'thumbs' trouble, they go with my worn out brain I think. :D

Brian.
 

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