Posted on Jan 12, 2013

Integrated circuit Ul is connected as a low-frequency asymmetrical oscillator. Its output is inverted by Ql and fed to the reset te

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rminal of U2 at pin 5. Integrated circuit U2 is configured as an audio oscillator and is enabled when the output of Ul is low. With the voltage at pin 5 of U2 constant, the circuit just" "bleeps."" The voltage across capacitor CI is fed to the base of Q2, which turns it on and grounds pin 5 of U2. When the frequency of the reset signal on pin 4 falls, the output frequency of U2 rises. The output then becomes a whoop, starting low in frequency and ending high. Resistor Rl sets the repetition rate and R2 determines the time duration of the whoop. Resistors R3 and R4 set the center-operating frequency.

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