Wailing Alarm Siren, Schematic

Parts List:
R1,R3,R5 = 10K                            C1 = 10uF/25V, electrolytic
      R2 = 75K                         C2,C3 = 0.01uF (10nF), ceramic
      R4 = 220K                           C4 = 470uF/25V, electrolytic
 IC1,IC2 = 555 Timer/Oscillator     D1,D2,D3 = 1N4001
      Q1 = 2N3055                         LS = Loudspeaker, 8 ohm     

A complete KIT plus Printed Circuit Board will be available soon. 

The circuit above provides a 'warble' alarm-call generator that simulates the european 'dee-dah-dee-dah' type sirens used in several european countries.

In the circuit, U1 is wired as a tone generator and U2 as a 1-Hz astable multivibrator, but in this case U2's output is used to frequency-modulate U1 via R5, the action being such that U1's frequency alternates between 440 and 550 Hz at a 1-Hz rate.

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Copyright © Tony van Roon