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Astable oscillator frequency adjustable siren

2016-08-25 07:24  
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Tone is made adjustable by using multiposition switch to change capacitors in oscillator circuit. Speed (rate of change in frequency) of siren is adjusted with R3. 4700-ohm resistor in series with R3 keeps siren op-erational when R3 is rotated to minimum-resistance position. Siren is operated by pressing switch to produce rising wail, then releasing switch until wail drops down to cutoff.The LM380 operates as an astable oscillator with the frequency determined by R2/C2. Adding Ql and driving its base, with the output of an  LM3900  wired as a second astable oscillator,acts to gate the output of the LM380 on and off, at a rate fixed by Rl/Cl.




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