Instructables

LASER MICROPHONE

Have you ever needed to hear a conversation in a room you are unable to access or bug easily? If so, and if that room has a window, you can using a laser microphone.

A laser microphone is a device that uses the vibrations of a window or similar pane of glass or plastic to record sounds near said window. A laser is pointed at a window and a photocell is placed where the laser's reflection lands. That photocell is then connected to a recording device. The vibrations of the eindow causes slight movements in the laser's reflection which, in turn, cause small fluxuations in the photocell microphone's current. This may seem complicated but it can be done cheaply and easily.
 
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Step 1: Things Needed

The things you need for this build are very easily obtained and cost me about $10.

TOOLS
Soldering gun( or just electrical tape if you're being really cheap)
Scissors( if you're using headphones)

COMPONENTS
A laser pointer $1.50
A photocell $.30
A bad pair of headphones or, as I used, a speaker cable ending normal headphone jack $3.80
A tripod $0.00( already had one and isn't needed)
Recording device or computer with recording software
vjackson42 months ago
its working with an led
but wen i connected a speaker to the breadboard its not givin any reply
shaggydoo1218 months ago
Also can I just plug the cord into a speaker so I can hear it ?
bioboy725 (author)  shaggydoo1218 months ago
In all honesty I am unsure. I had trouble when testing this and rushed to enter it in a contest. This instructable is practically unfinished and I have been meaning to remove it until I have had the time to fix it. Sorry for being unhelpful.
shaggydoo1218 months ago
Please explain placement of the photocell . I'm new to this and want to build one but first I need to understand it.
Couldn't you pull an infrared laser diode out of an old cd drive?
I just got in a 480mw IR laser to try one of these. Will be making a guide as I do It. I have worked with the real thing once before I retired form law enforcement. Aiming the IR lasers are the fun part. We used a digital video camera but your phones camera can see IR qlso.
50-501 year ago
I am so anoyed at you for beating me to this idea, I was going to enter this but needed to order more photocencors.if you could better explane how this works you have a very big chance of winning.
Ian01 50-501 year ago
You might beat this if you find a way to make it ignore ambient light. (Hint: TV remotes do it.)
bioboy725 (author)  Ian011 year ago
One of the last steps already mentions infrared lasers. I just didn't have the time as I was going on a school trip and couldn't wait for the stuff to be shipped.
I didn't mean lasers. I meant modulation.
bioboy725 (author)  50-501 year ago
Well thank you for the feedback. I knew someone else would have the idea so I kind of rushed it. I bought everything that day and did it all quickly. I am working on improving the instructions now so I hope that helps.
Tanmay Das1 year ago
You can also use an infrared laser and receiver instead of ordinary laser.
IR is invisible to the naked eye so you won't get caught and also any other outside light will not interfere with the receiver.
bioboy725 (author)  Tanmay Das1 year ago
I mentioned that at the end but I was rushing to get this up before anyone else could, so it was poorly worded.
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