is it possible to use an raspberry pi to detect ultrasound of 40000 Hz ? if so what parts and what software. and i want to have a small screen that readsout the Freq. would help me a lot! Thanks for the input 
Look at this Analog Ultrasound Range Finder. It shows parts to build both a transmitter and a receiver. This is used as a distance locator of any object using 40 KHz ping measuring the time delay. Parts list and theory included.
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so i could maybe build this and remove the receiver ? and only get the feed back in KHz instead of range ? to big help thanks !
ops i meant transmitter hehe
ops i meant transmitter hehe