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ECE 492 - Computer Engineering Design Project
Ultrasonic Rangefinder
Matt Johnston & Brett Griffin
2013
Introduction
Theory
Ultrasonics have been used for decades in a wide
variety of industries. Ultrasound is a sound
pressure wave that oscillates at a frequency higher
than that of audible noise. For our application,
ultrasonic transducers were used in conjunction
with the Altera DE2 development board to create a
accurate rangefinding system. The transducers can
be set up side-by-side to detect the distance of
other objects or, for increased range
demonstrations, set up across from one another
pointing at each other.
Ultrasonic transducers typically contain a small
piezo-electric crystal inside. When this crystal is
subjected to an oscillating wave at its
Results
With the transducers set up parallel to one another
and sensing the range of a different object we were
able to obtain a range limit of ~3 feet with errors
of around ±1 inch. When pointing at each other a
maximum range of ~7.5 feet with errors of ±1 inch
was obtained.
With increased signal verification in software
using a cross correlation algorithm, we believe the
range and accuracy of the system can be improved
on.
Fig. 4 Block diagram of system
Fig. 2 DE2 interfacing hardware circuitry
resonant frequency, it generates an ultrasonic
sound wave at that same frequency. A different
transducer then receives this wave, causing its
crystal to oscillate at the same frequency. This
analog oscillation can be converted to a digital
signal and interpreted using software via the DE2
board. By measuring the time difference between
the transmit and receive signal, distance can be
measured.
Testing
Numerous different hardware and software
components were required to interface our system
with the DE2 board. Multiple VHDL components
were created for different purposes. These
components were tested individually to ensure
proper operation.
An analog to digital converter was also required
and was interfaced with the DE2 board with a
custom driver component created in VHDL. Black
box testing was also done on the ADC before
integration testing was done.
Fig. 1 Transducers set up at 1 ft. distance
Goals
The goal of this project was to create a system that
could reliably produce ranges up to ~10 feet when
the transducers were pointed at each other. Our
goal was to also design a system that could be
adapted for a wide variety of applications. The
hardware was designed such that only changes in
software are required for different applications.
An Op-amp was also needed to amplify the output
peak to peak voltage of the receiving transducer.
Adequate gain was needed to increase the distance
limit of the rangefinder.
Fig. 3 Transmitter with receiver response
Once all hardware components were operating
properly, integration testing was done to ensure
proper operation of the system as a whole. Most
integration testing/debugging was then done in the
NIOS II IDE to tweak the accuracy of the system.
Extensions
As mentioned, the hardware was designed with the
intention of being adaptable depending on
different applications. We believe this system
could be used as a leak detection system for a gas
pipeline. By using transducers to measure
transmission times of the sound wave through a
moving fluid, we can accurately detect changes in
the fluid velocity. Changes in fluid velocity could
be attributed to undesirable changes in flow rate
caused by a leak.
This system could be realized by increasing the
accuracy of the signal detection. No changes need
to be made to the physical hardware of our design.
Proper care would need to be taken to ensure that
the system is properly coupled to a pipeline to
decrease signal attenuation.
Department of Electrical & Computer Engineering