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Sound Impact Sensor Details? — Parallax Forums

Sound Impact Sensor Details?

SRLMSRLM Posts: 5,045
edited 2010-03-25 20:27 in Accessories
According to the documentation for the sound impact sensor (link) the module detects changes in sound levels. This makes me think that the module does not actually detect sound levels, since changes in sound levels is the first derivative. Can anybody clarify?

Also, if the change is sustained is the pulse sustained? In other words, does the output work like the PIR sensor?

Finally, what's the current draw and the startup time? Does the module need to self calibrate like the PIR?

I'm looking to use this module to detect the passing of trains.

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Post Edited (SRLM) : 3/23/2010 8:58:57 PM GMT

Comments

  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2010-03-23 21:41
    It looks from the photo like it uses an NE555. A schematic would've been a nice touch, though. (But for $7.99, you could just buy one and try it. smile.gif )

    -Phil
  • LeonLeon Posts: 7,620
    edited 2010-03-24 07:23
    I don't see how a 555 would work in that application, it must be an op amp.

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    Leon Heller
    Amateur radio callsign: G1HSM
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2010-03-24 09:05
    Leon, I thought that, too. But if you look closely at the enlarged photo on the product page, you'll see that the chip says NE555. Pin 1 is grounded, and pin 3 goes to an LED, both of which are consistent with a 555.

    -Phil
  • LeonLeon Posts: 7,620
    edited 2010-03-24 10:10
    I wouldn't have thought that an electret mic would have enough output to trigger it, but you must be right.

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    Leon Heller
    Amateur radio callsign: G1HSM

    Post Edited (Leon) : 3/24/2010 10:15:12 AM GMT
  • Jessica UelmenJessica Uelmen Posts: 490
    edited 2010-03-25 14:45
    Hi all,

    Sorry it's taken me awhile to jump in on this, but attached is the schematic for the Sound Impact Sensor RevB. We'll be adding it to the product page as well!

    @SLRM - Yes, you are correct, the sensor detects changes in sound, not the actual level. The maximum current draw of the sensor is 3 mA, and it does not require a startup time like the PIR. I just did some tests using my Droid as a "boom box", and the pulse was able to be sustained during for fairly long intervals (in relation to a 2:11 song) during certain parts. During other parts, the output fluctuated between 0 and 1 rather frequently (usually during times when the bass wasn't as prominent).

    I hope this helps, let me know if there's any other questions!

    -- Jessica

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    Jessica Uelmen
    Education Department
    Parallax Inc.
    pdf
    pdf
    Sound Impact Sensor RevB_Schematic.pdf
    15K
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2010-03-25 15:54
    Thanks, Jessica! That clears up the mystery.

    Leon, 'looks like we were both right. There are more parts on the bottom of the board, and the mic goes through a preamp before hitting the 555.

    -Phil
  • LeonLeon Posts: 7,620
    edited 2010-03-25 20:27
    I thought there must be something like that. I've seen similar circuits and they all have an amplifier.

    I've got a small dsPIC with an electret interfaced to the ADC via a similar amplifier, biased at half the supply voltage, which could perform the same function.

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    Leon Heller
    Amateur radio callsign: G1HSM

    Post Edited (Leon) : 3/25/2010 8:38:44 PM GMT
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