Analysis of Implementation

 

1.1     Cost of Components

The total cost of components used in the experiment is approximately $130, as calculated in Appendix B.  This amount is acceptably low for sonic radar to be viewed as an inexpensive alternative to other altimeters, should the final solution be realizable.  Additional costs will be incurred from the microprocessor hardware, display and component housing.

1.2     System Capabilities

The system was tested using a variety of surfaces and at a variety of distances.  The following chart summarizes the results obtained:

 

Surface

Actual Distance

Time Taken

Calculated Distance

% Difference

Attenuation

Person

  1.32 m

    7.6 ms

1.30 m

1.5%

5.2%

lab ceiling

  2.11 m

  12.1 ms

2.08 m

1.4%

3.1%

wall - green paint

  2.16 m

  12.5 ms

2.14 m

0.93%

5.2%

white board

  3.84 m

  22.0 ms

3.77 m

1.8%

46.2%

wall - white paint

  6.52 m

  37.2 ms

  6.38 m

2.1%

68.8%

wall - green paint

19.93 m

115.6 ms

19.83 m

0.50%

-

 

Calculated distance values are the result of dividing the time taken in half and then multiplying by the speed of sound.  For the calculations above, it was assumed that the speed of sound was 343 m/s, which may be inaccurate.  Attenuation was calculated by noting that when the microphone receives an echo from a surface within 1m away, it appears at the output as 29V peak to peak.  The peak-to-peak values of the echoes were measured and compared against this value of 29V in order to determine the percent decrease in signal strength.

 

It should be noted that the values for actual distance were measured by hand using a measuring tape, and this may have incorporated further error.  On average, however, the difference between actual distance and calculated distance were 1.5%. This error will translate to an accuracy of approximately 2cm when distances within 2 meters are taken which is acceptable for use as an altimeter.

 

While the experiment is capable of receiving an echo from surfaces further away than 20m, these greater distances could not be tested when the other measurements were taken.  Unfortunately, the lab equipment could not be signed out, and in order to measure longer distances extra leads had to be attached in order to place the microphone and speaker in a hallway, as the oscilloscope and function generator were locked to lab benches.  As a result of the extra connecting wires, a lot of noise was added to the output signal when it was viewed on the oscilloscope and the input signal lost power as well.  The test at 19.93 m was run under these circumstances, and attenuation could not be calculated due to the extra noise in the signal and channel.  At a distance of 50m, the echo was undetectable due to the noise.  However, when the experiment was run previously without the extra leads, an echo was noticed after reflecting off a green painted wall approximately 52m away.