Ultrasonic receiver picks up frequencies about 30 khz above human hearing range. Using frequency division, sounds between 20-50 khz are divided by 16 with a binary counter that converts the sounds to clicks. The microphone boosts faint sounds, such as bugs walking in bark and animals eating. It also limits loud sounds, such as chainsaws, dirt bikes and airplanes.
I have used the ultrasonic receiver to listen to bats and some insects such as katydids and grasshoppers. You know those curly lightbulbs GE is making us buy now? They are really loud in the ultrasound range, much louder than flourescent bulbs. Listen
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