DIY Spy Ear reverse engineering
Here is a project that I have often thought of. I hope we have all seen those amplifier spy toys for like a dollar. I have often thought of grabbing one, and using the circuit to make something cool. It would probably work as a headphones amplifier. You could even stick it into an altoids can. I am not sure if it would power a larger speaker, but I bet you could push it a little. It would have to be modified, and I have not researched it. It seems that this device is using a filter to just pick up conversation ranges and filter out background noise. Some capacitors could be changed to make it HIFI. It would not be ideal but would work.
Now this Instructable actually does a little more than just use this circuit. He actually reverse engineers this project. It is a fairly simple circuit. All you really have to do to reverse engineer something is to make a list of the parts on the circuit board, and then follow all of the traces and see where they connect.
There are several ways of doing this. On a simple one or two layer board, you could simply visually follow the traces. You could also use a multimeter to find the connections. In this article, he actually takes a picture of the front and back. He then goes to photoshop and pulls of the traces on the back of the board. He flips it around, and places it on top of the front of the board. He then visually drew a circuit.
You can see the final circuit below. Article via Make
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