Step 3: Rig the Reciever

Phototransistors work very similarly to microphones in that they vary the current they allow to pass through them when exposed to chaning light levels. So, treat the phototransistor like a mic, and attach it to the MIC port on a laptop, or to the MIC terminals of a preamp, then hook the output of the preamp to the input of an amplifier.

If you are using a preamp, you should be able to screw the leads of the phototransistor right onto the back of the device, but if you are using a laptop, you will need to tape or solder togeather the pins of the phototransistor to the wires of a stripped headphones chord. Remember the ground (-) lead of the phototransistor is the one that has a little flat spot on the plasitc. Look to the photos for help.
<p>Wow, super cool build! Will this work on double-paned windows (like ones for cold climates)? Also, will the subjects of your surveillance be able to see a laser dot? Thank you.</p>
hi , dear ,i am thankful to you for your this work done on this area , i need your help in this project as i am also doing my project in my university but i am doing on IR beam of 980nm and 50mW <br> i dont know how to detect this IR beam and then after striking on window i.e target how to demodulate this IR beam into audible sound. i seriously need help please
Which is cooler...<br /> <br /> stick C4 in any object, light it and it will instantly be cooler.<br />
This link isn't direct laser communication but it is a way to transmit data through laser beams (especially sound)<br/><br/><a rel="nofollow" href="http://www.metacafe.com/watch/2225704/make_a_simple_laser_communicator/">http://www.metacafe.com/watch/2225704/make_a_simple_laser_communicator/</a><br/><br/>It has only been tested by transmitting sound but other encoded data should work to.<br/>Also this actually is direct communication except it is transmitting data in area of affected particles that cannot be heard (the electromagnetic spectrum)<br/>
sorry,grammar error <br>
funny cause you only use 1 laser wire
These laser bugs are fun! Here is another nice one...<br><br>http://www.lucidscience.com/pro-spy%20gadgets.aspx<br><br>Now the neighbors are no longer safe!<br>
Where can I get a microphone preamp?
sending 2ch stereo over laser using polarized beams is interesting, the cheap plastic &quot;REAL-D&quot; 3d glasses you get from cinemas for about 75p ($1) would be a start.<br /> &nbsp;what about the receiver? a kinda 2way mirror at 45D to split the beam in two then use two phototransistors?<br />
You could use the linear polarization filters from traditional polarized 3D glasses. The Real-3D glasses however use a combination of quarter wave-plates and linear polarization filters to enable decoding of circularly polarized light. So, you are better off using the old (and cheeper) glasses, or ordering a larger sheet of filter from a supplier.<br /> <br /> If you want to see a working 2ch system in action, check out my blog post where a few guys and I&nbsp;tried it out. Rough schematics and video included:<br /> <br /> http://hotwigati.wordpress.com/2008/11/15/polarizing-optoacustic-mixer/<br /> <br /> Happy Hacking,<br /> &nbsp;Chris<br /> <br />
Or light a c4 parcel, throw it at the window with timing and you'll get what you want.<br />
Thos ol' 56Kbps modems; i got mine from there
radio shack $3
<a rel="nofollow" href="http://www.digikey.com">http://www.digikey.com</a><br/><br/>Search &quot;audio transformer&quot;.<br/><br/>(I am not affiliated with this vendor)<br/>
That's only true for backwards-compatible ones.
i got a question for you. where can you find an ir laser? any links?<br/>also i have a suggestion. there are some goggles you can make with theatrical gel that lets you see along the ir spectrum here is the link<br/><br/><a href="http://www.instructables.com/id/Homemade-Infrared-Goggles!-For-Under-$10/">http://www.instructables.com/id/Homemade-Infrared-Goggles!-For-Under-$10/</a><br/><br/>let me know what it does if you try it!<br/>
Ok you guys will think this is funny. If you know your being spyed on just constently move the window. These things work by <em>feeling</em> vibrations. So but somthing that buzzes on the window.<br/>
There was an episode of Burn Notice where they knew they were being listened to by laser so they taped a turned on vibrator to the window.
how appropriate........
Do you need the radioshack circuit board kit to make this? and is that a 50k ohm linear taper potentiometer? And i cannot find an infared laser, will red work?
No, you don't need the radioshack board. It was just a convinient platform to build upon. And I would recommend using a RED laser first, because infrared lasers can be dangerous (You can't tell when your eyes are being damaged!). - Good luck!
A few questions (they might be silly ones, I don't know, I'm not very scientifically minded...): - What if you shone your laser through an infrared filter? I guess what I mean is: do green/red lasers emit any infrared light that could be filtered? - If I were to use processed negative film as an infrared filter, would the laser burn a hole through it? - What strength lased did you use? - Would plugging the mic. jack into a MP3 player, rather than a laptop still work?
- lasers only emit a single wavelength of light, so a green laser emmits only a negligable amount of infrared.<br/>- depends on the strength of the laser (a laser pointer shown here, definately not)<br/>- I went into staples, office depo, and wallmart and looked at their laser pointers. Then i bought the cheepest one i could find that was actually a laser (some of the &quot;laser pointers&quot; just have a red led and their beam diverges very fast, so it is useless). Long story short, a rather weak laser.<br/>-the MIC output from the laser reciever needs to goto an amplifier or pick-up of some sort. Plugging it into an MP3 player will do nothing.<br/>However, you _can_ use the MP3 player's signal to modulate the laser beam at the transmitter, and you will hear the music at the reciever. For that, look at this project: <a href="http://www.instructables.com/id/EEPBZGCJP1EPH67K7Q/">http://www.instructables.com/id/EEPBZGCJP1EPH67K7Q/</a><br/><br/>&gt; they might be silly ones, I don't know, I'm not very scientifically minded...<br/>they are good questions nonetheless. what good is a scientist if he keeps his mouth shut.<br/>
"- lasers only emit a single wavelength of light, so a green laser emmits only a negligable amount of infrared." This is quite plainly rubbish. Sorry to be so frank. Green laser diodes do not exist; instead an infrared laser diode is used. This is called DPSSFD technology. (Diode Pumped Solid State Frequency Doubled) An infrared laser at 802nm pumps a tiny block of Nd:YAG to double the frequency to 532nm. Therefore unless it is a quality green laser it will not have an infrared filter inside it to remove the infrared that can be emitted. A supposedly green laser can generate 80% IR and only 20% visible green light. Also a laser needs to be at least 50mW before it will burn stuff. A cheapie laser (<$30) won't burn anything. Also a red laser will only emit a negligible amount of IR as a laser diode can easily produce light at 652nm. (red laser light) Also if you are wondering how doubling the frequency halves the number: Imagine a sine wave. If you make the peaks twice as close together the distance between them is half as much. Or, imagine a line of bricks (or anything). Say they're 30cm apart. If you make them only 15cm apart (doubling the 'frequency' or how often they are there if you walked past them) the distance is halved. Sorry for the long comment.
it may just be a typo pal, but you don't measure frequency in metres, you measure it in Hertz (Hz), wavelength is measured in metres (and naturally, nanometres as you get down to these levels). Again, apologies if you mistyped that, but it's fairly important.

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Bio: I am a student and hobbiest. I'm into physics, linguistics, sailing, electronics, hacking (not cracking), music, and the like. I post most of my ... More »
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