# Keys Finder Electronic Schematics > Miscellaneous > Keys Finder

 General:Imagine that is morning , you barely anticipate the bus for work and you can't find your keys. If you suffer from this situation frequently, this circuit is ideal for you. A fizzle is the only thing you have to do. The overall circuit is small enough to attach it to your keys.

Description:

The ear and mouth of the circuit is a piezoelectric buzzer. Fizzling in a frequency of 3...4 KHz produced sound waves that piezoelectric buzzer converts them to an oscillation. This oscillation  passes thought C1 and thought  inverters N1...N3.The inverters along with R1 and R2, compose an amplifier with gain 400 ! .The C8 and C9 stabilize and reduce the signal's level.

Next the signal rectified from D2 and D3. The integral circuit Ν4, C3 and  R5 ensures that the circuit will not  triggered from common noises but only from late fizzle. When the output voltage increases at N4, Τ1 cuts off  and the input of Ν4 goes to high logical level. It's output goes to <0> and C5 is charged, through R9 until N5 changes operation state.

Click on the image for the full version.

Next C5 discharges  and everything is starting from beginning .The AC voltage goes thought the buffer circuit of T2 to buzzer witch starts to fizzle. There is a small problem in this point, the buzzer will never stop fizzling because the output signal triggering the circuit again thought C1. This is solved in this way: when the buzzer sounds (until C3 discharges thought  R5), the input of Ν1 goes through D4, C7 and D3, to high logical state. In this way until the buzzer stops the input of the amplifier can't receive and amplify any given signal.

Parts

 R1 =10k R2, R5, R8 =10M R3, R4, R6, R7, R9 = 100k R10 = 4k7 C1 = 22n C2, C7 = 47n C3 = 560n C4 = 10μ/16V Tantalum C5 = 1n5 C6 = 100n C8 = 56n C9 = 15p D1...D4 = 1N4148 T1, T2 = BC547B IC1 = HCF4069UBE

PCB

Title: Keys Finder
electronic circuit
Source: www.electronics-lab.com
Published on: 2005-02-10