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Bird and animal scarer for crops and airports - uses frequency modulated audible output between 12 khz and 20 khz at differing repetition rates and for varying durations
Bird and animal scarer for crops and airports - uses frequency modulated audible output between 12 khz and 20 khz at differing repetition rates and for varying durations
The frequency of the circuit is modulated according to an exponential sawtooth law and the device switched on and off automatically using a photosensor at dawn and dusk. The form of modulation is designed to imitate an animal call with the frequency rising for about 0.5 second, falling for about 0.25 s and being stable for about 0.5s, the actual frequency being less important. The element of surprise is important, and the repetition of the signal should not be simply periodic. A 0.833Hz square wave with a mark space ratio between 1 to 5 and 1 to 2 is passed to a 2nd order low pass filter and the output used to modulate a VCO. The VCO output is switched to an amplifier and loudspeaker by a FET controlled by a clock circuit with two potentiometer controls to set the duration of emissions between 10s and 2 minutes and the number to between 2 and 15 per hour.
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