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.
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
There is a small problem in this point, the buzzer will never stop
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.
|R2, R5, R8 =10M
|R3, R4, R6, R7, R9 =
|R10 = 4k7
|C1 = 22n
|C2, C7 = 47n
|C3 = 560n
|C4 = 10μ/16V
|C5 = 1n5
|C6 = 100n
|C8 = 56n
|C9 = 15p
|D1...D4 = 1N4148
|T1, T2 = BC547B
|IC1 = HCF4069UBE