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Velocity/Accelerometer w/Digital OP??

Discussion in 'General Electronics Discussion' started by RyanC, Mar 5, 2015.

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  1. RyanC

    RyanC

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    Mar 5, 2015
    Hi guys!

    I am new to this forum and relatively new to electronics, I come from an industrial automation background so I have had a little experience. Firstly I have to say, reading some of your posts and replies on here has been truly mind-blowing, I definitely aspire to gain the knowledge that some of the members on this forum have.

    Now on to my question...

    I am searching for a motion/movement sensor with a digital output. Not a PIR sensor though, a sensor that detects motion, i.e. is the car that the sensor is in moving? Yes or no.
    I don't need to know the velocity or speed or anything, just that there is movement. Would a velocity sensor or accelerometer give me a digital output? Or is there another sensor that I do not know about?

    Any help would be much appreciated.

    Thanks in advance!

    Ryan
     
  2. Gryd3

    Gryd3

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    Can you describe your motion?
    If it's a smooth linear movement, then once the object is travelling at a consistent speed an accelerometer will no longer provide any measurements.
    So you really only have a couple options here...
    A distance sensor.
    Take frequent measurements, and if the measurements are changing the object is in motion.
    An accelerometer.
    Again... take frequent measurements, but 'log' them. There is a little Calculus required here, but you can determine velocity given the readings and time stamps from the sensor. I know you do not need to know the velocity, but a small microcontroller can simply output a 1 or 0 based on if the estimated velocity is anything other than 0.
    Gryo ;)
    I like these, mainly due to the name... these detect changes in orientation, so they will not tell you if the object is sailing across a pair of rails, but it will tell you if your object has turned, or rotated.

    Any combination of the above!
    The Nintendo Wii system uses an accelerometer and gyroscope to detect controller motions. You can also find an 'IMU' that can provide this information.
    The draw back is that my proposed solutions require a microcontroller... If you can provide more details, then perhaps we can suggest a simpler detection method.
     
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  3. BobK

    BobK

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    Jan 5, 2010
    The laws of physics make it impossible to sense motion in the way you are asking. Moving relative to what? The car may be parked, but it is spinning around with the earth and revolving around the sun. Is it moving?

    That said, an accelerometer can tell you if the car has changed it velocity in any direction.

    Bob
     
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  4. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Perhaps a GPS receiver will work, if you can get a good signal. Takes a few minutes to lock-in but after that most GPS receivers will report changes in position on a regular basis with a sensitivity of a few feet. More accurate position tracking is possible with mind-blowing data-signal processing. As @Gryd3 mentioned, you will need a microcontroller to actually implement anything robust. And perhaps a real computer if you need the super-accurate position reports.

    What is your application? We work better here if we know what the problem is.
     
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  5. RyanC

    RyanC

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    Mar 5, 2015
    Wow, thanks for the quick replies guys.

    Bob, I see what you mean. That makes total sense.

    Gyrd3, it sounds like an accelerometer with a micro controller is what I need then :)

    hevans1944, a GPS receiver is a great suggestion, however the application requires that the sensor works in all conditions - underground, in tunnels etc. The sensor will be used to turn on a flashing beacon while I am driving. Some of the sites I work at require it and I am sick of constantly having to plug and unplug it, I would much prefer to automate it if possible.

    I guess this means I need to do some more research on the working of the accelerometer. Thanks for your help and wisdom guys.

    Ryan
     
  6. duke37

    duke37

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    If your car is anything like mine, there is plenty of acceleration to detect when it is moving. Do you have glass smooth roads?
     
    BobK likes this.
  7. BobK

    BobK

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    Agree, I think an accelerometer + a delayed turn off would do the trick.

    Bob
     
    RyanC likes this.
  8. RyanC

    RyanC

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    Mar 5, 2015
    I'm not sure what you mean, but my sacasamometer is reading off the charts.
     
  9. RyanC

    RyanC

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    Mar 5, 2015
    Great, thanks Bob.
     
  10. Gryd3

    Gryd3

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    Jun 25, 2014
    At what speed do you need to turn your light on?
    An accelerometer will do great here, but would be subject to false positives if the driver or anything else caused movement in the machine. you would need tune the microcontroller to ignore these false positives.
    Additionally. If it's in a car, can you tap into the speedometer?
     
  11. RyanC

    RyanC

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    Mar 5, 2015
    Gryd3, it would need to turn on as soon as there is movement, say more than 3mph. Would the microcontroller require programming? Or are there "dumb" controllers, perhaps with dip switches or something?

    You really have to forgive my ignorance.

    I would be unwilling to tap into the speedometer as I would like the device to be portable. I would also like to keep the cost as low as possible as there are a few of the guys that I work with who are interested in the device and I would prefer to make it on the cheap side.

    Thanks!

    Ryan
     
  12. Gryd3

    Gryd3

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    Jun 25, 2014
    Well... having it auto turn on at something like 3mph would require that there is a fast enough 'start' for the accelerometer to sense. That or hopefully the road is rough enough to trigger it.
    There are 'vibration' sensors you can use, but the limitation expressed about the accelerometer would be compounded with no way to compensate.
    What kind of price point are you aiming for?
    Alternatively you could 'tap' into the car's ECU by reading messages from the OBD port. This is non invasive and can be plugged in/unplugged. programming for this would be harder.
    The only other thing I can think of other than those mentioned above would be an optical sensor aimed at the openings in the rims. (This would most likely get dirty in short order)
     
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