Subject:
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[MindStorms FAQ 4.5 How do I make a sound sensor?]
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Newsgroups:
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lugnet.faq
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Date:
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Wed, 14 Jul 1999 18:31:40 GMT
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Viewed:
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2170 times
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Subject: 4.5 How do I make a sound sensor?
Content-Language: en
Topic-Level: 0
Revision: Robert Munafo, 1999-07-14
Location: /robotics/rcx/
Comment: Topic-level is inaccurate pending a reference for topic
levels
<p>A rather complex circuit is required to read sound volume level in
an intuitive manner, if you want to respond to high-frequency sound,
or if you want to use your sensor in the RCX Code environment. The
circuit amplifies the signal from the microphone to make it sensitive
at a distance, turns it from AC to DC and detects peaks so you don't
have to analyze the waveform yourself, and sends the result through a
bridge rectifier so the sensor can be connected in either polarity to
the RCX input. Here are two Web pages describing specific
implementations:</p>
<blockquote>
<a href="http://www.plazaearth.com/usr/gasperi/sound.htm">
http://www.plazaearth.com/usr/gasperi/sound.htm </a>
<p>
<a href="http://www.kabai.com/lego/lego.htm">
http://www.kabai.com/lego/lego.htm </a></blockquote>
<p>If you're reading the input at a sufficiently high rate, a much
simpler solution is to hook up a microphone directly to the RCX input.
The RCX can read its inputs at a rate of about once every 3
milliseconds (about 330 Hz) but you'll have to use NQC or LegOS to
achieve this rate. Also, your sensitivity will drop off drastically
above this frequency, and you'll have to take several samples and
compute the RMS power level yourself.</p>
<p> Passive microphones (the kind that don't use an internal battery)
are essentially sound-dependent resistors and most have a resistance
range that lends well to being used as an RCX input (actually this
isn't quite true -- a microphone is a resistive load in series with a
small current source, but when you put 9 volts across the microphone
you can ignore the small current source). The microphone would be
attached and wired to a LEGO® conducting plate in a way similar to
the light and temperature sensors discussed elsewhere here.</p>
<p>Other things to note: "Mini condensor" mics will only be useful if
they are the kind that don't have extra connections for a DC power
supply. A cardioid (directional) mic is probably more useful than a
nondirectional mic because it allows you to determine direction just
by rotating. </p>
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Message is in Reply To:
 | | [MindStorms FAQ 4.5 How do I make a sound sensor?]
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| Subject: 4.5 How do I make a sound sensor? Content-Language: en Topic-Level: 0 Revision: Robert Munafo, 1999-07-13 Location: /robotics/rcx/ Comment: Topic-level is inaccurate pending a reference for topic levels <p>Passive microphones (the kind that (...) (25 years ago, 13-Jul-99, to lugnet.faq)
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