Subject:
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Ultrasonic Sensor iS "Slow"
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Newsgroups:
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lugnet.robotics.nxt
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Date:
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Fri, 7 Sep 2007 21:02:31 GMT
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Reply-To:
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<dickswan@*IHateSpam*sbcglobal.net>
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Viewed:
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22852 times
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Original Thread title was "Re: Ooops! NXT Software Comparison
correction / I2C Messaging Speed". I've renamed as worth a separate
thread.
> John Hansen wrote on September 05, 2007 3:40 PM
>
> The errors that occur are that the sensor does not properly report
> variable distances as it is positioned at varying distances from an
> obstacle. If you slow down the read rate then it works correctly
> (i.e., with a wait of ~15 ms between read transactions) but without
> that delay it does not accurately reflect the varying distances as
> it should. I'm not talking about getting bus errors - just invalid
> distance readings from the sensor.
You're right!! If you poll the sensor too fast, it definitely reports
wrong distances. I'm doing some more testing to characterize the error
performance.
For example, if you poll every 2-msec then it almost always reports 22
to 24 cm as distance regardless of the "real" value. A slight increase
in the delay and the reported distance seems to increase to a longer,
but wrong value.
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Message has 1 Reply:
 | | Re: Ultrasonic Sensor iS "Slow"
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| (...) The 15 ms that John reported is the time it takes for a sound pulse to travel 500 mm, the round trip distance at the maximum advertised range of the US sensor. An interesting coincidence? Roger Glassey (17 years ago, 11-Sep-07, to lugnet.robotics.nxt)
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