It's been a while and I wanted to expand a little bit on my June intelligent car post and discuss collision avoidance technology in a little more detail. All collision avoidance technologies use sensors that collect information that is processed by onboard computers in the car. Let's talk about ultrasonic parking sensors today.
Ultrasonic parking sensors are typically mounted in the bumpers and used for parking systems. Effective distance for a transducers depends on the circuit and signal sequencing that is being used so the sensitivity varies across different devices. Parking sensors are designed for relatively short parking distances of 0-5 feet.
You may have noticed them on car bumpers and wondered what they were. Here's a close-up picture of one on an Audi A4 (pic source: goo.gl/fOhcQy). They are about the size of a nickel.
Distance is commonly indicated by a sequence of beeps and the closer the obstacle is to the sensor the faster the sequence of beeps until a continuous tone is emitted indicating that your bumper about one foot (or less) away from the obstacle. Here's a short 58 second demonstration video demonstrating BMW's Park Distance Control (PDC).
Ultrasonic means above the audio frequency range and these sensors typically operate somewhere between 40 kHz and 70 kHz. In future posts I'll describe camera, radar, and lidar systems.