End Course Project - Sound sensor general tests

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Date: 29.11.2007
Duration of activity: 1 hour
List of participants: Alessandro, Daniela, Samuele

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Goal of the day: Before definitely choosing our project, we had to make sure that the Lego sound sensors are enough good to be used for the physical implementation of our idea.

Plan:

• Find out if the Lego sound sensors can be used to recognize the direction and/or distance of some sound source
• If so, define under which conditions it works better
  
• Plan some tests to be done later in order to clarify some details of our project

Requirements formalization - An agent of our project:

• must be capable of recognizing the distance of a sound source, using the read value (amplitude).
• must be capable of recognizing the direction from which a sound is spread, by using two sound sensors, or by pointing a single sound sensor in different directions.
• should be nice if it was capable of distinguishing among two or more different sources, by means of their frequency - in case of a pure frequency sound - or their spectrum - in case of a mixed frequency sound.
  

General tests
We wrote a simple program that just outputs the reading from a single sound sensor. Then we made the first test, to see how the sensor behaves as a directional sensor.
We generated a buzz with our laptop, and moved the sensor around the room to see if values actually changed a bit. We got only slight value changes.

Then we tried to improve the directionality of the sensor, by building a paper cone around the sensor. We ran the same "approximative" test, and we got very good results: high values when directed to the source, low values otherwise.


We then built a simple tester robot. We mounted the sound sensor upon a motor,

and we wrote a program that made the sensor rotate by 90 degrees in all four directions, and sample for a while in each direction. Then print out all the mean sound values.


We tried some different volumes, or with different distance, and we ended up with readings around 60 in the direction of sound, 40 in the opposite direction, and 30 in the other two directions.

We concluded that the sound sensor behaves as we hoped (actually only for near loud sounds sources as far as we know) and it could therefore be used for our project.

We noticed that the sensibility range goes from low frequencies, around 200Hz to high frequencies over 1kHz, but the sensor has different sensibilities, depending on the frequency range, for small frequency variations.

We noticed a trivial thing also, that we didn't think of before: sound waves bounce on the wall, and are heard from the sensor as if they came from the opposite direction (this is why the sensor outputs greater values when pointing in the direction opposite to the sound source).
We plan that if this problem will affect our agents in their sound locating capability, we could build an environment for them in which sound doesn't bounce on walls, by removing walls (and we would need a very large room) or by making sound absorbed by walls (by covering walls with something).

Further tests plans:

• Identify which frequencies can be used by our sound sources, in order to be geographically localizable: we will measure how the sound perception falls, by getting far from the source. We will discard then frequencies that are perceived too weakly from a reasonable distance.
• Then we must analyze the sensor behavior with the presence of more than a sound source

Conclusion:
As far as we know we could build our agents. We will do further tests in some days.