INTRODUCTION, CIRCIT DIAGRAM AND WORKING
Spy ear is the devices which converts low power audio signal to high power signal and gain. It can be used in Theaters , Concert halls, Lecture rooms, Trains, Court houses, Conference rooms, Embassies, Gaming facilities, Recording studios, Aircraft , railways ,bus station etc.With this sound amplifier, you can now hear things crystal clear that you could never hear before. Spy ear is very easy to use, just put the ear buds in your ears - aim the Spy Ear towards what you want to hear and things are heard crystal clear. Spy Ear has adjustable volume control, which amplifies sound up to 50 decibels. Spy ear is also great for watching TV late at night, while your spouse sleeps you can keep the sound on the TV way down and still hear clearly.
In spy ear circuit the most important part which is used to amplify the ckt is An IC named LM386N, which is a low sound amplifier, it amplifies the sound which is received by the condenser mic connected in the ckt. The LM386 is a power amplifier designed for use in low voltage consumer applications. The gain is internally set to 20 to keep external part count low, but the addition of an external resistor and capacitor between pins 1 and 8 will increase the gain to any value from 20 to 200. The inputs are ground referenced while the output automatically biases to one-half the supply voltage. The quiescent power drain is only 24 mill watts when operating from a 6 volt supply, making the LM386 ideal for battery operation.
Spy ear is widely using in the spy works. Many spy agencies, National Security Agencies using both wired and wireless spy ears to hear the private conversation and to cought any illegal person doing any illegal work.
What binoculars do to improve your vision, this personal sound enhancer circuit does for listening. This lightweight gadget produces an adjustable gain on sounds picked up from the built-in high-sensitivity condenser microphone. So you can hear what you have been missing. With a 6V (4×1.5V) battery, it produces good results. a small signal amplifier is built around transistor BC547 (T1). Transistor T1 and the related. components amplify the sound signals picked up by the condenser microphone (MIC).
The amplified signal from the preamplifier stage is fed to input pin 3 of IC LM386N (IC1) through capacitor C2 (100nF) and volume control VR1 (10-kilo-ohm log). A decoupling network comprising resistor R5 and capacitor C3 provides the preamplifier block with a clean supply voltage. Audio amplifier IC LM386N (IC1) is designed for operation with power supplies in the 4-15V DC range.
It is housed in a standard 8-pin DIL package, consumes very small quiescent current and is ideal for battery-powered portable applications. The processed output signal from capacitor C2 goes to one end of volume control VR1. The wiper is taken to pin 3 of LM386N audio output amplifier. Note that the R6-C4 network is used to RF-decouple positive-supply pin 6 and R8-C7 is an optional Zobel network that ensures high frequency stability when feeding an inductive headphone load.
Capacitor C6 (22μF, 16V) wired between pin 7 and ground gives additional ripple rejection. The output of LM386N power amplifier can safely drive a standard 32-ohm monophonic headphone/earphone. Assemble the circuit on a small general-purpose PCB and house in a suitable metallic enclosure with an integrated battery holder and headphone/ earphone socket as shown in . Fit the on/off switch (S1), volume control (VR1) and power indicator (LED1) on the enclosure. Finally, fit the condenser microphone (MIC) on the front side of the enclosure and link it to the input of the preamplifier via a short length of the shielded wire.