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UltraSound Transmitter ?

Discussion in 'Electronic Components' started by Stef Mientki, Oct 31, 2003.

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  1. Stef Mientki

    Stef Mientki Guest

    hi,

    I'm thinking of making a simple 3D location circuit, for multiple target
    points.
    I've the feeling that Ultrasound is the cheepest and a (quiet) reliable
    way to perform that task.
    I once saw a system, called "graphbar" (almost 15 years ago), that
    performed 2D measurements, in a area of 40*40 cm, with a resolution of
    about 0.1 mm (I'm not sure about that, but it was quiet remarkable).

    One of the problems with ultrasound seems to make a "wideband" pulse, or
    in other words creating a puls with a fast rising edge.
    The trick the "graphbar" used was to make sparks over electrodes a few
    millimetres apart.

    Are there any other ways (and don't like sparks) to create fast rising
    ultrasound pulses, with enough power ?
    Does anyone know some interesting links about this subject ?

    thanks,
    Stef Mientki
     
  2. Sverre Holm

    Sverre Holm Guest

    http://www.sonitor.com/news/article.asp?id=24
    Sverre
     
  3. I's not directly what you are looking for, but I've published some time ago
    an aritcle in Circuit Cellar on a "3D scanner" using ultrasounds (July 2001,
    Circuit Cellar Ink #132). The idea was to mount a pair of 40KHz tranducers
    on two servo motors, and to scan the environnement. A PC software then built
    the 3D image. It was working correctly, however the key limitation was the
    low angular resolution (may be 5-10°, dépending on the objects). It was
    enough for robotics applications, but not for actual imagining. Moreover the
    ultrasounds are not really easy to work with, in particular incident objects
    could be completely missed (beam reflected anywere but not on the
    receiver...).

    Friendly yours,
    Robert Lacoste - ALCIOM : The mixed signals experts
    http://www.alciom.com
     
  4. I built an ultrasonic ranger system. One way to generate reasonable edges is
    to use a motor driver chip. I used an SN754410 running at 12V, which worked
    pretty well. Its got a power and logic voltage input, so you can clock it
    using TTL levels.

    Regards,
    Bob Monsen
     
  5. Stef Mientki

    Stef Mientki Guest

    hi Robert,

    maybe not exactly what I'm looking, but it still sounds very interesting.
    I tried Circuit Cellar on the web, but your article doesn't seems to be
    on line.
    Is there a way to view the arcticle somewhere ?

    thanks,
    Stef Mientki.
     
  6. Stef Mientki

    Stef Mientki Guest

    hi Bob,

    That might be a good idea.
    What kind of transducers did you use ?
    And can you tell anything about the accurarcy ?

    thanks
    Stef Mientki
    I used an SN754410 running at 12V, which worked
     
  7. I used cheapo electronics goldmine 40kHz transducers, about a buck each,
    IIRC. It was actually only used to detect motion, so I don't know about the
    accuracy. Relative changes were detected by a little opamp circuit. However,
    viewing the thing on my oscilloscope, I would trigger on the transmitter,
    and display the receiver's waveform. It was easy to see that the relative
    phase shifted very rapidly as I moved an object towards and away from the
    system. 1127m/s means the wavelength at 40kHz is about 28mm. So, the phase
    would shift through 2pi for every 14mm I moved the object.

    Your problem, however, is timing accuracy, and being able to generate enough
    energy to get a good return. Also, detection of the wave. For actual
    ranging, I'm not sure how to detect the edge, unless its so large in
    relation to the ambient noise that it wakes up all the dogs in the
    neighborhood... Waiting for a PLL to lock takes too many cycles, I think, so
    an LM567 is out.

    Post the circuit to alt.binaries.schematics.electronic once you get it
    working, it would be fun to see it.
     
  8. I've recently been tinkering with some 24kHz transducers that I found at
    a local surplus shop. Using 5V and driving directly from a PIC, I can
    ping the ceiling with good success. ;-) I'm not sure what the max
    range is yet as it's still on a breadboard with probes and clip-leads
    attached all over it. I'm going to change it so that I have a
    transistor in typical grounded emitter between the PIC and the
    transducer. I'll use a 5mH inductor in parallel with the transducer.
    This serves the purpose of actually allowing the transistor to conduct
    since the transducer doesn't pass DC. It will also pump the 5V to about
    40V really giving some kick to the transducer.

    You can read all about how it should work here:
    http://www.ee.latrobe.edu.au/~djc/UltraSonics/Ultrasonics.htm

    Obviously not my idea, but hey that's what the internet is for, right?
    ;-)

    BTW, I know what you mean about the phase shifting based upon the
    distance. I wasn't expecting to see that, but I figured that the
    reflecting sound was canceling
    I use a 741 op-amp to get some voltage gain from the other transducer
    (which is connected to both inputs of the 741 in differential fashion).
    That then feeds directly to an LM393 comparator that is biased about
    10mV higher than the idling output of the 741. The 393 gives me a nice
    5V square wave to feed into the PIC. It seems to work pretty well, but
    a more modern replacement for the 741 would do a better job. The Q of
    the transducers is so high that they are virtually deaf to sounds that
    are off the resonant frequency. False triggering is not near as much of
    a problem as you might think, but a well timed loud hand clap close the
    transducer can mess things up. As far as accuracy goes, it seems fairly
    consistent but there is a definite but likely quite predictable
    propagation delay thru the op-amp and comparator. I guess the biggest
    problem with this way of doing it is that I can't tell how strong the
    incoming reflections are.

    Using a 16bit timer incremented every 1uS gives a max range of about
    10mtrs, but very high resolution. I guess theoretically that would give
    me close to .01" resolution, but I haven't done any real consistancy
    testing yet.

    michael
     
  9. Oops, I should proof read more.

    I meant to say that I think the reflected sound cancels the outgoing
    sound when it's out of phase. BTW, I send 5 cycles of sound and usually
    capture 5-30 reflections depending upon the distance. The tricky part
    is figuring out which one to pay attention to. ;-)
     
  10. Stef Mientki

    Stef Mientki Guest

    Looks indeed a quiet good idea.
    Yes !!
    I think that's even the reason why the evolution of mankind and animals
    differ ;-)
    And indeed it's an interesting page !
    That's dilemma I noticed too.
    For having high accuracy, you need a very low Q (or in other words a
    very high bandwidth, or still in other words a very fast edges).
    On the other hand, to suppress unwanted signals you want a small
    bandwidth. So I'm not sure what's the optimum.
    False triggering is not near as much of
    Yes, but that kind of "noise" could be simple removed by repeated
    measurements.
    As far as accuracy goes, it seems fairly
    I don't think you're interested in the strength of the signal, only in
    the time delay.
    That reminds me of another trick: "time controled gain" (I cann't
    remember the correct term. The idea is: after sending an US pulse, you
    should gradually the gain of the input amplifier. The longer the sounds
    travels, the more it's amplitude drops.
    Yes theotically ...
    but then you've to measuere temperature and humidity very accurate,
    because they influence the speed of sound considerable !
    speed = alfa* SQRT ( T / M )
    see for instance this page
    http://hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe3.html#c1

    thanks,
    Stef Mientki
     
  11. It's surely simple and effective. What more could one ask for? ;-)
    I thought you might like it.
    I don't know how much actual delay is caused by the transducer vs. the
    delays in amplifying it. At any rate, I would suspect that they should
    be predictable. It seems that maximum resolution would come from using
    as high a frequency as possible. I see that the "professional" sensors
    use frequencies far in excess of 100kHz.
    This is true.
    Yes, I've seen this done and it's really the right way to do it IMO.
    Polaroid does this IIRC. I just have a simple 1.5mS blanking period to
    avoid detecting the transmitted signal directly and to allow the sending
    transducer to stop ringing.

    In one implementation I saw, the guy had a target placed at a fixed and
    known distance from the sending transducer. This afforded him great
    accuracy and adaptability to current conditions. He would just ping it
    a few times and come up with a constant that was applied to all
    following calculations. I would think that he still needed to treat
    transducer reaction time and amplifier delays as a seperate constant in
    the equation. I could see that temperature would even modify that to
    some extent. I guess you just have to figure all these things out and
    see just how much of an affect they have on the big picture.
    If I ever even achieved .1" accuracy, it would still be far better than
    my needs. I was doing this as the groundwork for some simple robotic
    "eyes" to avoid running into things, so the first reflection pulse (that
    isn't caused by the receiver directly hearing the sent signal) is all I
    needed.
     
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