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Wailing Alarm Siren by Tony van Roon Parts List: R1,R5 = 4.7K C1,C4 = 100uF/25V, electrolytic R2 = 47K C2,C3 = 0.01uF (10nF), ceramic R3 = 10K T1 = 2N3702 (NTE159, TUP, etc.) R4 = 100K IC1,IC2 = LM/NE555, MC1455P, etc Rx = *Notes LS = Loudspeaker. *Notes Notes: This circuit provides a warbling sound to any alarm circuit. IC2 is wired as a low frequency astable with a cycle period of about 6 seconds. The slowly varying ramp waveform at C1 is fed to pnp emitter follower T1, and is then used to frequency modulate alarm generator IC1 via R6. IC1 has a natural center frequency of about 800Hz. Circuit action is such that the alarm output signal starts at a low frequency, rises for 3 seconds to a high frequency, then falls over 3 seconds to a low frequency again, and so on. *The Loudspeaker LS and the resistor marked "Rx" should be...

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