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Bells and G Forces

Discussion in 'Electronic Basics' started by Ryan, Feb 23, 2007.

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  1. Ryan

    Ryan Guest

    I'm looking into the idea of home growing a door chime beginning with a
    magnet switch on a door. (All the wireless kind I've seen have crap
    range and only one receiver and no visual alert.)

    I want to make one audio chime and then in a more distant location, make
    a second audio chime with a light too.

    As a beginner, and sometimes slightly more than that, I'm not sure what
    methods exist to activate a short "ding" or electrical pulse that
    doesn't continue through the duration of time that the door is open.


    ~

    On another topic, I am interested in measuring G force with
    acceleration. I've searched around a little bit, but would appreciate
    a pointer in the right direction.

    I'm wondering the name of a circuit/device that can be used measure
    change in velocity. I'm curious how difficult it is (for an
    electronics non-genious) to take measurements / read voltages / design
    circuits based on the outputs of this device.

    The maximum expected change in velocity is about 15 feet per second per
    second.


    Thank you.
     
  2. A "one-shot" is a device that generates a single pulse when triggered.
    There are many circuits, but the simplest way to generate a pulse when a
    switch closes is to put a capacitor in series with the load. The
    combination draws a pulse of current, then looks like an open circuit once
    the capacitor is fully charged. If the load is the coil of a small relay,
    you can drive a bigger load without needing an inconveniently large
    capacitor. You will need some path for the capacitor to discharge
    through when the switch opens, such as a parallel resistor.

    A gadget that measures acceleration is called an accelerometer.
    Tiny solid-state ones are made, but I haven't looked up the prices lately.
    If you don't need accurate calibration, it's fun to experiment with
    homebrew approaches, such as a mass on as spring with some way to measure
    the deflection, or a phonograph cartridge (Do they still make cheap ones?
    It might be easier to buy an old turntable at a thrift store.) with a
    small mass attached to the stylus, or maybe a U-tube with colored water
    and an optical liquid-level detector. The acceleration you mention is
    about half a gee, so you don't need great sensitivity.
     
  3. Bob Masta

    Bob Masta Guest

    On Fri, 23 Feb 2007 04:03:00 -0500, "Stephen J. Rush"

    If you are just experimenting, and don't need small size, you
    might want to try a speaker as the mass-on-a-spring sensor.
    You will need to attach the desired (non-ferrous) mass to the center
    of the cone. Measure the response from the speaker terminals.
    This system will measure acceleration along the axis of the
    speaker; the speaker suspension prevents motion in other
    directions.

    Best regards,


    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    www.daqarta.com
    Scope, Spectrum, Spectrogram, Signal Generator
    Science with your sound card!
     
  4. JeffM

    JeffM Guest

    The switch doesn't move and is not mounted on the door.
    Space the switch off the door frame so that the magnet PASSES it.
    Use normally open contacts or invert the state.
     
  5. Gareth

    Gareth Guest

    Ryan wrote:

    [SNIP]
    Have a look at some of the datasheets and see what you think. I think
    that in the simplest form they just produce a voltage proportional to
    acceleration. Others give out pulses with different duty cycle
    proportional to acceleration.

    Analog Devices make small accelerometers,

    http://www.analog.com/en/subCat/0,2879,764%5F800%5F0%5F%5F0%5F,00.html

    Freescale have a range of similar devices

    http://www.freescale.com/webapp/sps/site/overview.jsp?nodeId=0112691118


    --
     
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