If you want to build an ultrasonic range finders project but you don’t want spend much money to buy commercial sensors like Parallax’s PING sensor then Kerry D. Wong’s project may help you to build sensitive ultrasonic range sensor using inexpensive ultrasonic transducer. It takes cost less than 5 dollars (excluding the MCU).
The project uses cheap 24 kHz transducers. These sensors can easily achieve a range of more than 20 feet with properly designed circuits. The ultrasonic transmitter is powered from ATmega328’s counter 1 PWM output (chip pin 16 and Arduino digital pin 10). It uses the bridged output to achieve the maximum output power of the transducer for a given supply voltage. The Receiver used a two stage inverted band-pass operational amplifier LPC662. Each stage has a gain of around 67 (36.5 dB) and the circuit has a combined voltage gain of 73 dB.