Created: Dec 15, 2016
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In electronics engineering applications, ultrasonic sensors are device that detect obstacles by emitting ultrasonic waves that are beyond the hearing range of a human ear, and then calculate the distance of that obstacle based on the time it takes for the ultrasonic wave to hit the object and for the sensor to receive the echo. Ultrasonic sensors can be used in many applications. One application of an ultrasonic sensor shown in this reference design is to display the distance of an object or an obstacle behind a vehicle. In this design the ultrasonic sensor detects the object or obstacle and sends the time information to the microcontroller. The microcontroller will display the distance on an LCD display.
This reference design is a simple sensing circuit but significant especially in automotive applications. When someone parks a vehicle, common accident is that the driver hits a child from behind since the side and center mirrors of the vehicle are not enough to make sure that no one is at the back. This circuit can help the driver detect obstacles behind by implementing an ultrasonic sensor. The operation of the circuit starts when the microcontroller sends at least 10 microseconds of high pulse to the ultrasonic sensor to trigger it. The sensor will emit an eight cycle of 40KHz ultrasonic burst to hit an object. The reflected ultrasonic burst will be picked up by the sensor receiver. After receiving the reflected ultrasonic burst, the sensor will send a high pulse to the microcontroller with a width proportional to the distance of the obstacle. The width of this high pulse which is in a microsecond unit will be divided by the microcontroller with a number of 58 if the distance is in centimeter or 148 if it is in inches. After dividing, the result will be displayed on the screen of the LCD. The circuit can be powered by the vehicle battery by using a DC-DC converter to step down the 12V to 5V.
The application of an ultrasonic sensor in this reference design is commonly used by car manufacturers these days. In fact, advanced innovation similar to this application involves automatic braking to surely avoid accident. Some car companies do not limit the installation of this sensor at the back. They also install some sensors at the side of the vehicle to monitor if there are cars near that are on the blind spot.