We are looking to use ultrasonic sensors for our 4th year design project, and was wondering if anyone could recommend some sensors for proximity detection, as large range as possible. Should we build our own Rx/Tx pair, or are there modules made for this purpose already?
Check this ultrasound sensor from polaroid, it can meassure distance from 6 inches up to 35 feet. It comes with the signal conditioner board so you don't have to design and build it, you just have to make the program with the uC you are using or make a control circuit to command the sensor.
I think it costs less than 100 dollars, not sure really, check it on the internet.