To meet modern safety expectations and driver’s convenience, parking-assistance systems have become quite popular. To ensure safety, they generally use ultrasonic transducers to measure distance from nearby objects, which acts as a decision to control a display or other outputs, or sent to a MCU for further processing using a communication interface.
Most important consideration in designing an ultrasonic park-assist system is selection of ultrasonic transducer according to its maximum range, minimum range, ringing time, type (enclosed or open), and some more characteristics. Ultrasonic transducers or transceivers are devices which create and detect ultrasonic sound waves by converting electrical energy to sound energy and vice-versa. These transducers can’t reliably detect objects within minimum range, typically 0 – 0.3m. The maximum detection varies from 1.0 m to 10.0 m depending on factors such as the power supplied to the transducer, signal gain and signal-to-noise ratio (SNR) of the circuit.
Further, a designer can select a transducer that can be enclosed or open. To increase ruggedness and reliability, most park-assist systems use enclosed transducers. A tradeoff with open transducers is low performance by being less effective at energy conversion, difficulty in implementation, and requirement of gain to achieve the system’s requirements.
Ringing time is another important factor in design. When the sensor/transceiver has transmitted sound waves, the system should wait for some time before waiting for the return signal for the transducer to stop “ringing”, or else, it would always measure a distance of zero. This is because it detects the ringing signal before the signal has diminished.
If you want to get further details on the design of Ultrasonic Park Assist systems, here are some industry standard reference designs describing them with complete documentation:-
Ultrasonic Park Assist with Blind Spot Detection:
TI offers a reference design intended for applications such as ultrasonic park assist, self parking, blind spot detection and valet parking. The design is based on a highly programmable SoC with integrated 8051 core and supports small form factor. The SoC provides all signal conditioning and processing for the transducer echo signals and calculating the distance between the transducer and objects. More on this Reference Design
4-channel Ultrasonic Distance Measurement for Parking Assistance:
This design from Cypress builds a four-channel ultrasonic distance measurement system for ultrasonic parking-assistance applications (UPA). The design uses Cypress’s PSoC 1 devices which are a best fit for UPA applications, and includes an example project and reference hardware design using PSoC 1. More on this Reference Design