Ultrasonic distance measurement with microcontroller

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Dr. Iváncsy Szabolcs
Department of Automation and Applied Informatics

In this thesis work, some of the common uses of ultrasonic rangefinders were presented. The basic idea behind ultrasonic range finding and its inner workings were also introduced. Environmental factors affecting the speed of sound were pointed out, like temperature and humidity of air. An approximate formula for calculating the speed of sound was determined, which is a function of temperature. The ultrasonic rangefinder was designed, with the description of the used components and schematics. The whole implementation process was also described including PCB Layout, Component Layout and assembly. Algorithms used in the software were presented with the help of flow charts and timing diagrams. The user interface was also showed.

Ultrasonic distance measurement requires precise timing, because the time slot between sending and receiving an ultrasonic pulse has to be measured accurate to the microsecond, else measurement results could suffer from serious errors. With increasing distance, weakening of the ultrasonic signals introduce an inaccuracy of tenths of millimeters, which is clearly demonstrated by the ultrasonic rangefinder implemented in this thesis work. Another considerable factor is the exact knowledge of the speed of sound. Tests results showed, not considering the temperature, make errors grow by an order of magnitude. They also showed that changes in humidity do not have a great impact on the speed of sound. Extra precision gained by considering humidity is insignificant compared to the timing errors introduced by weakening signals. This makes measurement of humidity pointless regarding ultrasonic range finding.


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