laser17This experiment is for advanced students.Did you know that when you talk inside a house, the windows vibrate very slightly from your voice? If you stand outside the house and aim a laser beam at the window, you can pick up the vibrations in the window and actually hear the conversation inside the house.


Remember how windows split a laser beam in two from the Laser Basics experiment? That’s the basic idea behind it. First, I’ll show you how to build your own space-age laser communicator, then you can work on your spy device.


The first thing we’re going to do is take the music from your stereo or MP3 player and transmit it on a laser beam to a detector on the other side. The detector has an earphone attached, so someone else can listen to the music from your laser. Weird, huh?


Here’s how to build your own:


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30 Responses to “Space-Age Laser Communicator”

  1. It is best to use a laser pointer, because the pointer has the circuitry to properly drive the laser diode.

  2. ericksonnationmom says:

    for the laser could i use a diode module red laser?

  3. Unfortunately you do need a laser for this experiment – a flashlight will not work. It has to do with how the light is produced.

  4. One more question I do not have a laser so is their anything that I can substitute with. Shayaan

  5. That’s a good question, I am going to ask you to do an experiment for me. Since there’s enough current for magnetic earphones (the regular earphones with wires attached to a plug, not bluetooth), try using it in parallel with the photocell and tell me if it works. I *think* it should, so let me know what happens?

  6. simmons_jr says:

    Does it need to be a crystal ear peice?

  7. trganzhorn says:

    OK! So witch lead of the LED should i solder to the black wire from the battery pack? Or does it not matter?

  9. trganzhorn says:

    What should you do if you have a non bipolar LED?

  10. The video and the parts list is correct – you want a 220 Ohm resistor. Jameco put in a “standard picture” of the resistor because there are so many of them (it’s not even a real image of what you’ll be getting), but if you check the title and description, the size is correct (220 Ohm). Does that help? Thanks for asking – that is really confusing esp if you haven’t build one of these beofre!

  11. trganzhorn says:

    In the video you said that you need a red-red-brown resister. But in the material link goes to a brow-black-orange one. Which one should I get?

  12. The way it looks is not nearly as important as what is inside. The audio transformer from Radio Shack is this one:
    https://www.radioshack.com/products/radioshack-audio-output-transformer?variant=20332216325

    and you can also get it from Jameco:
    https://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10001&productId=2210511&langId=-1&catalogId=10001&ddkey=https:CookieLogon

    Have you seen the replacement parts spreadsheet? It has all the numbers you need on it with order links:
    https://www.sciencelearningspace2.com/2016/08/radio-shack-component-replacements/

  14. No, you can also just point a laser at the window and watch for the reflection spot on a wall, and watch how it moves slightly when noise happens inside the room. That will show you vibrations are happening. If you want to actually hear the conversation, then you need to modify the experiment a bit.

  15. Malcolm Smith says:

    Hi Aurora,
    Do you have to use the Space-age laser communicator to pick up the vibrations in the Windows?
    Thanks! Juliette-14

  17. Yvonne Myers says:

    Hi Aurora! I am having trouble finding the audio transformer. Our Radio Shack didn’t have one that looked like the one in your video and I’m not certain which one to get from Jameco. Could you provide me with an order number please?

  19. Shelley Harwood says:

    Hi Aurora!

    Can you chain multiple CDS cells together to make a bigger target?

    Thanks!

  21. Dan Archer says:

    I found another laser

  22. Dan Archer says:

    My laser has the spring on the back of the battery compartment how do I make it work?

  23. Arnav Wadehra says:

    Ok thank you 🙂

  24. Yes you can just use the amplifier. Just connect the two wires to another audio plug instead of the earpiece and plug it into the amplifier.

  25. Arnav Wadehra says:

    Could I use only the amplifier instead of using the crystal earpiece? If I could then how should I hook it up to the receiver?

  26. Trinity Wasankari says:

    I am 9 so i could not do this project it looks cool thank you though!!

  27. I’ll bet you can combine the solar cells from Unit 12 with this project and figure out a battery-free version! 🙂

  28. Lydia Fancher says:

    can it be solar?

  29. The 220-ohm works best – it’s a red-red-brown striped resistor. You should be able to find one at radio shack or equivalent, as you’re also going to need to find the audio transformer and earplug. Does that help? I believe the one in your kit was meant for the crystal radio project – what are the colors on the resistor? (Start from the non-gold end.)

  30. M Vanderkolk says:

    Do you have to have a 220-omh resister or can you use the resister you get in the International kit