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:MAKE A HIGH VOLTAGE SUPPLY IN 5 MINUTESSuper Easy E-mail Encryption Using Gmail, Firefox and WindowsMake a Voltage Controlled Resistor and Use ItMake a Ball Mill in 5 MinutesMake a Rechargeable Dual Voltage Power Supply for Electronic ProjectsSODA CAN HYDROGEN GENERATOR