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Picture of Hack The Spy Ear and Learn to Reverse Engineer a Circuit
This instructable introduces the venerable Spy Ear in details and my way to reverse engineer a circuit.

Why does this device deserves its own instructable?:

-You can buy a Spy Ear for a dollar!

-It can amplify sounds up to 60 dB or a factor of a 1000.

-It has a self limiting property and adjusts the gain so that the amplified signal volume is always just right.

-It runs of two LR44 1.5 volt button cell alkaline battery, so it's perfect for portable projects.

-Many of today's projects, such as in robotics, require analogue front end for sensing the environment and the Spy Ear circuit is just right to fill in as a multi-purpose front end amplifier.

-It is simple enough to reverse engineer.

-I am making another instructable using this device.

So the Spy Ear is a fantastic cheap,small and rugged circuit for modding and hacking

Check out my other Instructables:
Super Easy E-mail Encryption Using Gmail, Firefox and Windows
Make a Voltage Controlled Resistor and Use It
Make a Ball Mill in 5 Minutes
Make a Rechargeable Dual Voltage Power Supply for Electronic Projects

Step 1: How to Reverse Engineer a Circuit

Picture of How to Reverse Engineer a Circuit
This step shows you how to reverse engineer the circuit.

1. First take a picture of the front and back of the circuit.

2. Trace the pcb layout on the back using a graphic program like photoshop. Try using the "bucket fill" tool first. if that doesn't work color it by hand.

Don't color the whole pcb layout. Leave the areas where a solder is made clear, so that you can figure out which component's leg goes where.

3.Copy the pcb layout you made and paste it on top of the device's front picture. Flip it horizontally and adjust the scale and position so that the trace is super-imposed exactly on top of the components (see picture below).

4.Then comparing the different pictures and looking at the actual circuit, draw in the components' symbols from node to node. (see last picture).

5. Next, you'd need a circuit drawing program to rearrange the rough circuit that you drew by hand (see next step).

Count the components. Use the count as a checksum when you reconstruct the schematic. It is easy to forget something.

T0BY2 years ago

I am very impressed!

rickyjoy made it!4 years ago
Also,i had an talk with the chinese guy of which i
discussed with you before ,who works in the micro earpiece manufacturing
company,after a long talk he agreed to send me an beta circuit which is
used in this earpiece.He said i wont help you assembling or parts
finding. I'm just giving this circuit diagram and rest you work on it.

I had to pay him $ 93 for this circuit :(

Here is the circuit link to earpiece he gave.

Download Link to spy
earpiece circuit diagram:

Can you give me a schematic of the spy ear with 6v as the source? i m dying to get one!! plz giv me! thnx in advance!!
in step 4 , the capacitors that you have marked 2x100 uf did you use tantalum capacitors which have the number 107 written on them???
achraf527 years ago
Do I really need that transistor or use any type .
Biotele (author)  achraf527 years ago
yes any transistor will work.
Great you helped me from having to buy those type as I have so much ones but no one is this type, now I only have to grab capacitors and resistors and put them together .
static7 years ago
Back in the day, and even in the modern era I simply shine a pen light from the solder side through to the component side, to aid in tracing out the circuit. There are time when you will need a stronger light though, and that fatigues the eyes quickly, even young eyes. Nice idea here, but bucket fill generally gives me fits. I have learned to use [control]+S often.
Biotele (author)  static7 years ago
yes bucket fill is a pain. I am investigation using raster to vector programs as way to automatically trace the lines.
Dave543218 years ago
Wow that's great, here is another diagram of the Spy Ear from area 50
it allows you modify the Spy ear by removing a transistor and powering
it by the computer to make a super duper sensitive Condenser Mic
which worked well for me as I wanted a better mic than I could find at
radio shack.

here is the link to several directional Mic's the last one is the Spy Ear and also includes
the schematics.

also the .1 uf caps don't appear to be electrolitics so observe the DC potential
in this circuit when using electolitic caps by putting the + to the higher potential
so they don't blow up, which I doubt at that low voltage.
Biotele (author)  Dave543218 years ago
this is awesome. they also use the photoresistor/led pair from my other instructable as ACG.
I think you mean AGC automatic gain control. I don't know how the
photo resistorwould work in that circuit.

What lead me to the spy ear was I wanted to make my computer
mic actually put out some audio to make a series of affermation
statements to play while I sleep under my pillow. The little condenser
mic's that are powered by the computer audio circuit board lack
sensativity so you must speak closely to the mic and you pick
up a lot of unwanted noises made by the mouth that are not normally
heard in conversation.

What is the title of you other Instructable ?
burdockwing8 years ago
i have noooo idea what you are talking about its literally like you're talking gibberish
techh28 years ago
why this circuit dosent work please send me explication for this circuit plz plz i ned this circuit
Vaxinius8 years ago
Im trying to open your schematic in LTSpice and all I get is a bunch of text grid locations in a list. Need a bit of help with this. Bit new to this program but im familiar with programs like it. When i download the file it saves as a .tmp? Should that happen?
Biotele (author)  Vaxinius8 years ago
just rename them with their proper names "spyear.asc" and "", then open them with ltspice.
nope even when i rename the file i still get a spice error message that says theres "multiple instances of [symattr]"

then it lists a whole bunch of text of wire locations etc. same thing as before.

your help is appreciated as im a training electronics technician in the canadian forces and getting the edge on software like this can only do me good.
Biotele (author)  Vaxinius8 years ago
rename the extensions of both the files as ".asc" and try to opening them. I think the files are mixed up.

If that does not work Google "multiple instances of [symattr]". You might find the problem. keep me posted, thanks.

Turns out my problem was i didn't know how to properly rename an extension. Kept renaming the file the whole time. the sandbox!

Turns out my problem was i didn't know how to properly rename an extension. Kept renaming the file the whole time. the sandbox!
I'm trying to pair spy ears circuits with appropriate speakers. Do we know what a well-matched speaker would be? I know that under-powering speakers are a good way to damage them. I'm seeing .2 watt, 2 watt, 5 watt speakers out there.
Biotele (author)  mulluysavage9 years ago
the output impedance of the spy ear is ~70 ohms. Use an audio transformer. Beware, you will just have a lot of feedback.
thelandlord9 years ago
Just bumping this to let UK readers know "Poundland" has been selling these units for the last couple of weeks - I'm sure there must be a lot of ways to re-purpose these...
deltasoft10 years ago
Please visit here:

That is a good software of pcb reverse engineering
That is too easy for pcb reverse engineering.
Biotele (author)  deltasoft9 years ago
It says "buy now". Buying already made stuff is antithesis of DYI enthusiast. Is it only in chinese? Make an instructable showing how to use your software.
fkuk9 years ago
can you wire this up to a lm3916 vu meter?
so, which one the true..? i dont understand about these.
Biotele (author)  yuvensius Edulgensiano9 years ago
the first model. This is to show that there are variation.
skandar10 years ago
merci +ok
lewis9410 years ago
do anyone know where i can get a spy ear in the uk (shops/stores) coz i really want to give this a go but cnt get a spy ear and i not old enough to buy online so if anyone could help that would be fab lewis94 :D
iectyx3c lewis9410 years ago
eBay UK has it.
You do not need a credit card to buy online.
You can pay by Postal Order from your local Royal Mail Post Office.
Here is a link:
namzer010 years ago
there's something fishy about the schematics and the PCB Picture. They Don't Match!!! Please fix. I can't find where the 47uF capacitor is. in the schematic
thing 210 years ago
Where do I get it? (i live in usa)
raykholo thing 210 years ago
i believe that toys r us sells spy toys including this one, check online i also think u can just build the circuit yourself according to the schematic in this instructable and an online order from an electronics shop (digikey, allelectronics, the goldmine are some of my faves)...
sk8er610 years ago
I just want to make a pocket headphone amp for cheap, so could i just solder wires from a headphone jack to where the mic used to be? thanks
Biotele (author)  sk8er610 years ago
yes that will work. Except it will not be HiFi. You can change the capacitors like I did in one of the steps and increase the fidelity.
Grzegorz10 years ago
Try to use layers in Photoshop. What I am doing is taking the pictures of bottom and top then flip the bottom one and cover the top PCB picture with flipped bottom as different layer. Then you can set brightness and transparencies of layers (each one separately) for the best result. Even if they aren't exact same size you can stretch pictures to match the layers.
Biotele (author)  Grzegorz10 years ago
that is the best way to do it.
Lance Mt.10 years ago
I want to make this wireless, any ideas?
Biotele (author)  Lance Mt.10 years ago
sure. if you are lazy hook it up to an ipod car radio transmitter or an fmrs walkie talkie. if you want to build the circuit google "fm transmitter".
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