MintyBeam: Bug a room and transmit voice over a laser beam (also a Super Spy Ear/Stethoscope)

Contest Winner
INTRO: This instructable will show you how to make a laser voice transmitter and reciver housed in the infamous altoid tin (or any other clandestine container). If you choose, the receiver can be modified to also work as a Super Spy Ear AND an audio amp for your iPod etc. You can choose to make a RED, INFRARED (invisible), and GREEN version! The red is the easiest, smallest and cheapest to make and transmits almost 4 blocks (2/10ths of a mile), the infrared has obvious invisible top secret spy applications and lastly the green transmits CRAZY far and looks cool. You can power these circuits with a standard 9volt battery for several hours or choose to use a 23A which fits nicely into the altoid SMALLS tin but only powers it for about 25 min on full power...oh and the transmitters are adjustable so you can have a lot or a little laser light come out depending on how far/bright you want it.

THEORY: A LM386 audio amp chip takes voice from an electret condensing mic and modulates the intensity of a laserbeam, then the receiver uses another LM386 chip connected to a phototransistor to demodulate the laser and drives a speaker, headphones, or any other audio out (into a computer would be cool to filter sound!)


1-40 of 66Next »

Use 18650 Li-ion batteries instead, buy a battery holder from ebay and you'll have lots of power.

exagerated2 years ago
hey my circuit uses a lot of energy and the 9 volt battery lasts upto 30 mins plez help me to make it last little longer

You can wire additional 9 volt batteries together in parallel!

I know way late response but here is a simple link also.


good job!

Can i use the phototransistor which appears dark bluish black colour PLZ REPLY BACK!!!!!! I want to make this for my science fair!!
I like your project very much and want to build it badly!!!!!! I have some doubts
1 Can i use a 50mW laser with this circuit?
2 The laser is a 3v powered laser so if I use it with 9v in the circuit wouldn't it get burnt?
3 Is there any precautions to take to prevent burning the laser? By using something like a 4.5 v or 3v
4 Can i use a ir receiver with the laser?
5 Can i use a led and a Cds LDR instead of laser and phototransistor?
sgases2 years ago
i made the receiver circuit and im getting noise sound from the speaker. im only using a photoresistor and traditional 10K potentiometer :| help me please
zaphodd422 years ago
i know its been a while since this post, but i just finished my own version, totally based on your ideas! i had a blast and learned a ton. i used etched PCBs (because i just learned how), and modified some gorilla pods to magnetically mount the tins to them. in the photos, youll see i made a "collector dish" from polymorph plastic. thanx for a great 'ibble. on to the next weekend project!
exagerated2 years ago
hey also 1 more problem that my laser isnt that bright which it should i have tried changing the battery but that doesnt worked for me
hey.. can i use an ldr instead of phototransistor????
or a TSOP 1738 ?? will it work instead of phototransistor??
can i use anyother light source instead of laser diode??
drdan152 (author)  allsparkunleashed3 years ago
Good question !!!! My ORIGINAL idea was to use an IR led and it worked great but only transmitted like 6 inches then burned up the led after about a min ..... So maybe not so great ..... I even got a nice show of sparks and burned plastic kinda cool ..... I think the circuit just has too much amplification for an led but I wonder if a regular old light bulb or maybe a heavy duty led that take more voltage would work ..... Lemme know know If u try it :-)
better use an IR led.better for spying because it's not visible for human eye
but very low range rit??
10k Variable micro Trimmer is what I am not getting,

please tell me which one to buy is it this....


OR this


Please Reply

Please Reply or send the Link for the Part which I should Buy  ! !

Thank You !  ! :) :)
The first one is out of stock.....just had been to that shop

Can i use the second one instead ?
drdan152 (author)  akshay+jadhav3 years ago
Yeah sure it's just not as small :-)
I am doing this project,
So sir I do need ur help

I got a laser module which can barely handle 3V,so whenever i connect it just damages itself......so any idea how I could lower the voltage or any modification as per ur suggestion ?

drdan152 (author)  akshay+jadhav3 years ago
The first one is perfect !!!! Get that one or equivalent.
B.F.L.M3 years ago
So, Theoretically speaking, would this work if you removed/disabled the mic (maybe by adding a switch) and bounced the laser beam from the transmitter off of a window and into the receiver? Would you be able to hear whats on the other side of the window?

I would love to build this but i want to know if the above works so I know if i want to include an on/off switch for the mic on the transmitter.

Many Thanks,
{[Happy Building]}
drdan152 (author)  B.F.L.M3 years ago
That would be soo cool but in all my reasearch on "laser listeners" as they are called they really don't work all that great or at all and the aming is insanely hard and impractical and frustrating! Thats why i came up with this design is so i can still use lasers as a room bug. I guess theoretically YES you could experiment with it and is should work but im not sure how close you would have to be to the window and the window would have to be a certain kind so that it would vibrate with sound. If your goin to try it out i would build the reciver FIRST and then use a normal laser pointer in a constant on position and try bouncing the dot off the window into the reciver....and see if its worth adding an on off swithc to the transmitters mic!

Have fun experimenting!!!!
Excellent! Thank you very much ^-^

Many Thanks,
{[Happy Building]}
jdaley997023 years ago
Could you use a cone type shape or possibly old satelite dish to collect the beam and then put the photo resistor where the signal collects? I guess that would defeat the small size of it but for longer distances that may give a larger target and easier boost
why can't you use a concave mirror?????????
drdan152 (author)  jdaley997023 years ago
Theoretically yes ..... I have even seen like a white PVC pipe that collects the light into the phototransistor at the other end ..... A fresnel lense also seems to work really good at collecting light ..... U can get an 8 1/2 by 11 inch at a bookstore !!!!
drdan152 (author)  drdan1523 years ago
What's crazy is this thing seems to work BETTER when the laser light has had a chance to diffuse at long distances
Hmm I wonder if the diffusion leads to the extra static being lost because it's not the main part of the sound being transmitted?
hii.. i got the laser and still i am getting a humming sound of different frequency.. i am not geting the corect sound.. wen i touch the mike the sound changes a bit... thats all.. what should i do??
drdan152 (author)  allsparkunleashed3 years ago
How far away from the transmitter is the receiver ? Sometimes if your too close it won't come through clear ..... Farther away is better ..... So try aiming it from farther away and experiment with the alignment ..... If that does not work can you send me some pictures of the pcb you made and maybe I can look at the soldering and tracing ..... And see if I can spot the problem ..... I've made like 10 of these things and they always worked great ..... So maybe you have a wire crossed or your too close ? My email is danielstroupe@hotmail.com if u can send me pix
hii.. i completed the receiving part.. and i almost cmpleted the transmitting part. oly thing i need is a laser.. am on my way to buy one..
mean while i thot of using an infra red led instead of laser.. and whenever i bring the ir led clos to the receiving part, its making a humming sound..like a bee humming.. i am not getting a perfect sound from the mic even if i adjust the 10 k pot.. will this problem b solved wen i replace the ir led with the laser??
drdan152 (author)  allsparkunleashed3 years ago
Hey !!!! It sounds like you built the receiver well and it works ..... It likes to hum like a bee when it senses light it beeps too ..... When I used an IR LED
it screeched and I occasionally got clear audio then it burned up and i got humming then nothing. I'm sure If u use the laser all will be fine :-) which laser are u gonna use ? Red ? IR ? GREEN ? If u live in the USA most grocery stores sell a laser cat toy in the shape of a mouse that has a really nice laser diode with wires attached already ..... You just have to hack it to bypass the off button.
can u help me in tuning the right frequency??

is this enuf??
drdan152 (author)  allsparkunleashed3 years ago
Just looked at your link to eBay ..... That laser is PERFECT for this project.
ok thanku...
i am from india.. i am planning to buy red laser.. 650nm.. i tried to buy from amazon but ther is no shipping to india. i tried to search on ebay but i am not able to find one that suits this.. there is not a thing called laser in electronic shops.. where can i find one??
hii.. my work is almost complete.. i went to a shop to buy some photo diode and photo transistr.. wen i reached my workshop, both these wer mixd together.. both are identical.. both look the same.. i dont kno which is which.. can u help me??
also, can we use an ir led intead of laser?
drdan152 (author)  allsparkunleashed3 years ago
Oh no !!!! I think I know what you mean ..... Some times when you buy a phototransistor it has a ir photodiode with it ..... But they both look the same sometimes And are easy to mix up ..... You could try to put 3 volts to each with 2 AA batteries and then try to view them with a camera to see which one is emitting IR and which one doesn't ..... The one that doesn't is the phototransistor. If you have an iPhone or a friend with one , the REVERSE camera works GREAT on detecting IR from LEDs.

As for replacing the laser with a diode ..... I tried it and it only worked for about 30 sec then burned up the diode.
sciencetor23 years ago
hey just a thought, since you won a pair of night vision goggles in the grand prize pack, they will make it a lot easier to aim the infrared laser, as they can see the light :)
drdan152 (author)  sciencetor23 years ago
Why YES it would !!!! I didn't even think of that !!!! Sweeeet ..... Thanks for
Your post :-)
1-40 of 66Next »