04-10-2012, 04:56 PM
ULTRASONIC RANGE FINDER USING MICROCONTROLLER
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ABSTRACT
An Ultrasonic or Sonar Range Finder is a common sensor in robotic systems and industrial environments. Ultrasonic sensors use reflected or transmitted ultrasonic waves to detect the presence or absence of a target component. The output is trivial in respect that the sensor merely detects whether the target is or is not within the design detection range.
Measuring distance with ultrasonic signals requires a transmitting ultrasonic transducer; a medium, such as air or water; a reflecting surface or object; a receiving ultrasonic transducer; and a time-of-flight measurement circuit. The sensing is initiated by first creating a sonic ping at a specific frequency. The transmitter circuitry consists of a micro-controller AT89C52 which provides the required 40 kHz signal and starts the timer. This is fed to a piezo-electric crystal which converts the electric signals to equivalent sound waves at the same frequency. These waves are made to transmit in air. Whenever any object is in the way of this signal, the signal gets reflected.
This reflected signal then travels back towards the transducer, again at the speed of sound. The receiver circuitry receives the reflected 40 kHz sound waves and converts into equivalent electrical signals at the same frequency using a piezo-electric crystal. The received signal after sufficient amplification is sent to a peak detector and a comparator which sends a high signal whenever a received signal is detected. This serves as interrupt to the micro-controller which stops the timer. This provides the round trip propagation time of the sound wave from transmitter to the object. Using the velocity of sound in air we can find the distance of the object from the transmitter.