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Ultrasound
The BowlsEye system uses ultrasonic waves in order to determine what is the closest bowl to the jack. A pair of MA40S4S transducers are excited directly from the Raspberry Pi. This produces a displacement in the piezoelement of the transducer, creating an ultrasonic wave which propagates in a forward direction. Once this wave reaches a material boundary where there is a mismatch in acoustic impedance, a reflected wave is generated with an amplitude proportional to the impedance mismatch. This wave then travels back toward the transducers, where it displaces the piezoelement of the receiving MA40S4R transducer, producing a voltage. This voltage is then captured by the Raspberry Pi via the ADC. The time to receive an echo signal is then calculated, based upon a thresholding condition to determine the echo location in the signal. The total distance to the object producing the reflection is then calculated as:
distance = (speed of sound in air * time for reflection to be received)/2
An 8-cycle wave is used to excite the transducer which provides sufficient energy in the received signal whilst minimizing the effects of coupling and interference between transmission and reception. This is generated through use of the pigpio custom waveform functionality.
