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Biotele writes –

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 100.
  • 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.
  • The Spy Ear is a fantastic cheap,small and rugged circuit for modding and hacking.

HOW TO – Hack The Spy Ear and reverse engineer a circuit – Link.