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laser transmitting sound over 1 mile

Discussion in 'LEDs and Optoelectronics' started by ahmed fathi, Jun 25, 2013.

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  1. ahmed fathi

    ahmed fathi

    Jun 25, 2013

    I am an engineering student , beginner in electronics , and I wanted to ask :

    If I try to make a transmission of sound using laser over 1 mile in the darkness, and about 50 meters in the light , how much would something like that cost , and where to start learning about what to do ?!

    to clarify : it is some kind of competition between students , ending in about two weeks , between teams not individuals

    thanks in advance
  2. poor mystic

    poor mystic

    Apr 8, 2011
    A very good practical worker with an excellent knowledge of physics and access to a decent workshop might succeed at low cost in a few days. A beginner might spend huge sums and several months, and blind himself or someone else - all for no result.

    To build such a project requires knowledge of communications systems, electronics, and laser physics.
    Lasers are very dangerous. I hope you are not thinking of actually building a system?
  3. ahmed fathi

    ahmed fathi

    Jun 25, 2013
  4. ahmed fathi

    ahmed fathi

    Jun 25, 2013
    and it is supposed to be for students , to raise their practical performance ..

    If you see no way to eliminate these serious dangers, I will ask them who suggested these conditions not simpler ones :)) .. Can't we use some laser pen , more powerful than the small common one but not that dangerous , or something like these lights used to emit light in the sky in celebrations or something ?
  5. davenn

    davenn Moderator

    Sep 5, 2009
    yes you could use a laser pen, tho there are other laser diodes that have a little bit more power you may find a laser pen is ~ 1 or 2mW where the max allowable in most countries is 5mW and 5mW laser diodes are readily available.

    you need to be able to modulate the diode power supply with the audio signal
    the audio signal just needs to be an electric condensor microphone and a 2 transistor preamplifier

    if you do use a laser pointer, then you will have to refocus its lens for convergence at a longer distance
    If you get another laser diode module, it needs to be one that comes with a collimation (focussing) lens

    at the receive end, you need another lens, a photo transistor or photodiode and appropriate circuitry to demodulate the audio from the laser signal

    The one used for into sky are a lot more powerful and are quite dangerous. For saftey you are better off staying with the low power ones

  6. poor mystic

    poor mystic

    Apr 8, 2011
    Nice one Dave and Ahmed - I hope I get to see how this comes out.
  7. wannabegeek


    Aug 17, 2011
    I'm working on a similar project....just for fun on my own...I PWM a 650 nm module pen laser with a 555 timer...would love to build a real driver of my own when I have the time...

    I use a cheap crystal mic and a biased op amp to center the signal to the 555's pin 5, works fine. I use a radio's ear phone out for testing.

    Sam's Laser FAQ is awesome...I so want to build a current source with optical feedback driver...just the basic ones are good practice for me.

    anyways....I would like to get my signal to go pretty far too, and at this point I have two issues...1) Need a Rx side lens and 2) I think the off set in my OP07 is preventing me from getting cranking up my gain on the photo diode. Gain is fine for now, but would like the option of going higher...I tried using a pot as noted in the OP07 data sheet but my 10K linear pot is not cutting it.

    Works great at just 17mA and no Rx lens at 50 feet.

    UPDATE: Found a funky old scratched plastic magnifying lens that looks like it could be from a drug store eye glasses repair decent.
    At 60 feet and 30mA, the 5mW 650 nm laser was about the diameter of a quarter. Didn't need the lens but it helped.

    Good luck !

    BTW, start with IR LED's way cheaper and safer...I was able to directly convert my Tx from IR LED straight to laser diode with no modifications.
    Last edited: Jul 1, 2013
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