Ultra-Sensitive Spy Ear

Have you ever tried to listen to a conversation on the other side of the wall? Or perhaps one across the street? Well, now you can!

Step 1: Materials

Most of the parts used in this project can be found in your local Radio shack.

Materials:
- small project box
- prototyping board 
- N-type battery holder
- A23 12v battery 

- LM386 op amp
- 100k Ω resistor
- 100k Ω variable resistor 
- 0.1 μF capacitor
- 0.22 μF capacitor
- 1 μF capacitor
- 100 μF capacitor
- electret microphone

- switch (optional)
- block connector (optional)
- 3.5mm(1/8") audio jack (optional)
- heat shrink tubes (optional)


Note: The values of the components listed above are not critical and may be replaced with other values, but testing them in the circuit on a breadboard before building would be a good idea.

Comments

[anubhavtalukdar007]

Can anyone give me a schematic of a spy ear circuit with 6 volts as source???

[hrhtml99]

Can someone please help me? I have constructed this and double checked everything, but it does not work. All i hear is a clicking buzzing sound! Please help!

[hrhtml99]

Please help! It can only pick up audio if i am talking like 1 inch away from the mic, i have checked my circuitry, and i have fiddled with the volume! Please help!

[anubhavtalukdar007]

Where will i get a LM386 chip?

[anubhavtalukdar007]

In India we don't have RADIOSHACK-like stores, so I want your help.
Thanx in advance for answering!

[ernie666]

Try www.digikey.com

[anubhavtalukdar007]

ernie666-
I hv a question- I got the lm386 but wat can i use instead of the 1uf tantalum and 0.22 uf capacitors? i dnt hv dem!!

[anubhavtalukdar007]

ok thnx dude
!

[Enjoying Electronics]

One question. Which side is the front of the IC? I'm assuming its on the right of the schematic. What is the pin load out? Where is 1 and where is 8? Thanks (I'm new to this :D)
Would a 9v battery work fine?

[ahebbar]

Can spy ear be done with wireless earphones???

[ernie666]

I don't see why it can't be done. You should try it

[KhajagB.]

thanks :)

[pavithraa]

we didn't get any output for this circuit with 9v. whether we need to change any resistor or capacitor value? advise us with value.

[ernie666]

You might want to check your circuit. LM386 chip has a wide supply voltage range. Maybe you connected the capacitors or microphone the wrong way, or maybe a component is broken.

[pavithraa]

reply us as fast as u can

[Alatec]

On the schematic, what are the pin numbers?

[ernie666]

oops. I forgot about that. The bottom left pin is pin 1 and the rest of the pins are numbered like it would be on a regular 8 pin DIP chip if you were to look straight down on it from the top

[DoctorDv]

You should enter this in the kit challenge. You would have a chance!
-Doctordv

[ekay3]

hey! I just wanted to ask that how much was the distance from which you can catch the sound and don't the wall's muffle the sound? I'm making it as my final semester project so want a pronto reply. :) waiting...

[nodoubtman]

I'm sorry, i tried that with hooking up a speaker, i heard nothing sorry.. :(

[KhajagB.]

can i use instead of 12V...9v ! if i replace the resistors with another numbers
?

[ernie666]

yes with 9v and different value resistors, but you should probably test them first because too much input power could cause distorted output

[KhajagB.]

or the capacitors!? plz reply ASAP

[ernie666]

yes

[Arjun123]

guys try shielded cable for noise interference definitely u will get results...

[Ram g]

its good

[slamdaddy]

The problem I've always had with anything that allows you to pick up sounds at a distance is that they amplify the background noise as well.
Would it be possible to add something similar to the technology used in noise-cancelling headphones to cancel out at least the sounds generated closer to the microphone?

[ernie666]

Noise cancelling headphones simply block sounds around you, so no this could not be used to solve this problem. If the noise is at a certain frequency, you could add a high/low pass filter, otherwise I don't think this problem could be solved without software. But you could focus on what you want to hear by adding a parabolic reflector like blinkyblinky suggested.

[slamdaddy]

I used a parabolic dish but still there was background noise, most of which came from much closer to me than the sounds I was trying to pick up. I didn't mean use noise cancelling headphones themselves to counteract this, I meant employ the technology that they use and integrate it into the circuit.
As I understand it noise cancelling headphones use a small microphone to pick up sounds just outside the headphones then play the inverse to cancel out the external noise with destructive interference. Would it not be possible to integrate this somehow in order to filter out the noise coming from closer to you so you're just hearing the sounds from further away?
Other than that, I think you're right and having various filters to tune out the frequencies you don't want would be the way to go.

[ernie666]

That sounds like a brilliant idea but I can't think of how to do that just yet. I'll try to figure out how to do this, and if I ever do, I'll write about it.

[slamdaddy]

Thanks, that'd be really awesome. I wish I could help but electronics is still on my to-do list.

[Pranjal Joshi]

can i connect signal output to 2 pins of earphone to turn on speakers in both ears?? reply fast

[ernie666]

yes

[xman2]

thanks you

[blinkyblinky]

Very nice, simple circuit. You should add a parabolic reflector for more sound collection...maybe a satelite dish or paper plate with foil?

[ernie666]

Yes, you could if you want.

[patito]

Sorry to ask this, but is it normal that the variable resistor is connected to positive and negative? It's like if a 100K resistor connected to a 12v battery.
I've searched the lm386 documentation, and there's no direct connection between positive and negative, only a capacitor.

[ernie666]

yes it is fine like that. the variable resistor is there to control the magnitude of the signals.

[zfuria]

I have already made 2 sets...1 has gt IC741 and the other has got IC 741 and LM368....bt the 2nd 1 is powerful....ut i cannot hear d sounds of d adjacent room clearly....the falling of pin is not heard at all.....so i your project is your sound that clesr and loud.....n wat about the disturbance created by microphone when kept near speakers?????i have ataached small 5 V speakers to it......

[ernie666]

walls my cause some disturbance to sounds from adjacent rooms. Speakers also cause some disturbance but I haven't figured how to solve this yet. I could hear pins drop in adjacent rooms because we have hardwood floors.