This is the simple circuit of a comparatively strong siren useful for any purpose. This circuit is based on two transistor. A complementary transistor pair (BC557 & 337) is arranged as an oscillator, directly drives the peaks. The figure is shown in below.
Transistor Q1(BC 557) is used to provide full charging of capacitor C2.When P1 is pressed, C2 discharges through R8 and the circuit starts oscillating at a low frequency that increases slowly until a high frequency steady tone is reached and it is kept. When P2 is released C2 starts discharging and output frequency slowly decreases. When C2 is charged fully the circuit stops oscillations. Adjust the values of C2 & R6 to vary the tune. Wire the circuit on a good quality PCB.A good quality common board may also do trick.
Parts List.
R1, R3 1K
R2, R5 10K
R4 220R
R6 220K
R7 22K
R8 100K
C1, C2 22µF/25V
C3 10nF
C4 47µF/25V
Q1, Q2 BC557 Transistors
Q3 BC337 Transistor
SW1 SPST Toggle or Slide Switch
P1 SPST Pushbutton Switch
SPKR 8 Ohm speaker
B1 12V Battery
Transistor Q1(BC 557) is used to provide full charging of capacitor C2.When P1 is pressed, C2 discharges through R8 and the circuit starts oscillating at a low frequency that increases slowly until a high frequency steady tone is reached and it is kept. When P2 is released C2 starts discharging and output frequency slowly decreases. When C2 is charged fully the circuit stops oscillations. Adjust the values of C2 & R6 to vary the tune. Wire the circuit on a good quality PCB.A good quality common board may also do trick.
Parts List.
R1, R3 1K
R2, R5 10K
R4 220R
R6 220K
R7 22K
R8 100K
C1, C2 22µF/25V
C3 10nF
C4 47µF/25V
Q1, Q2 BC557 Transistors
Q3 BC337 Transistor
SW1 SPST Toggle or Slide Switch
P1 SPST Pushbutton Switch
SPKR 8 Ohm speaker
B1 12V Battery
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