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Ultrasonic 3D Radar.

20 Aug

This page is next level of Virtual Touch Screen project. 

First things is a distance, for virtual touch screen its less than 3 m, because the reflective area is too small. For radar (or sonar) its different, and the bigger size of object the stronger echo. Approximated range of detection the object as big as a wall, 30 meters.

Technically, there are two hardware parts were added, to fully demonstrate extra ordinary sensitivity of the VTS project. First one is the BlueTooth module. And second is a tablet, running android. Device that I have, doesn’t support USB host mode (OTG), otherwise I may be fine w/o BT, just transfer a data over USB cable, as it was done in two previous demo video clips.  Have to say, it was not easy to represent 3D perspective on a flat screen, and picture below shows what I designed to complete a task:

android

Don’t think it requires a comments, the tricky part was to create an elliptical grid to show a distance. The number of circles is not limited to 2, I’d think about how to film next demo video, that ‘d show a “volume”.

Enjoy the movie:

There are two apples, and arduino measure position in 3D space both of them. X, Y, and Z coordinates plus P – power of reflected ultrasonic wave used to draw circles, with different colors. You can see movement of the red circle on screen when first apples moves.

edited on 21-08-2014

After thinking awhile how to show a “volume” on a flat tablet screen, I decide to remove filtering stage in a software, when a bunch of consecutive “layers” were shown as one single ring (object) on a screen. Now each packet of data received from single “spherical” layer creates a circle. As always packet includes X, Y, Z, and P. To make an image “clear” there are two others filters left over in the processing algorithm. One is rejecting data below ( selectable in a menu ) power threshold, and another rejects anything thats located farther specific (again, selectable) distance. This is why in a video you can see only a ball, but not me – operator making a movie.

Here is how the ball looks like on radar screen:

DSCF0480

And video:

That;s it for now.

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6 Comments

Posted by on August 20, 2014 in Uncategorized

 

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6 responses to “Ultrasonic 3D Radar.

  1. Apprentice

    August 20, 2014 at 11:38 am

    Hello,

    Nice demonstration improvement.

    Question:
    Can you use the value of the power of the returned (reflected) signal in conjunction with the position to estimate the size of the object? I don’t know if this is how a GHz Microwave Radar works.

    Best regards,
    João Carvalho

     
  2. magiciant

    August 20, 2014 at 3:31 pm

    I didn’t explain well, but arduino does estimate the size of the object based on reflected sonic wave power. See this 4 digits column on the photo, left side? They are X, Y, Z, and P – power. Radius of the circle-ring (apple) shown on the screen proportional to P. I know, that P is decreasing proportionally to Z^2, and to make size of the apple to change linearly with distance, I’m multiplying P by Z, removing ^2.

     
  3. Apprentice

    August 20, 2014 at 6:29 pm

    Hello,

    Question:

    For this project to be a full image radar the only thing that it doesn’t do, is the capacity to detect echoes that are close to each other than the time difference that a signal takes to reach the 4 receivers. In other words the discrimination of one echo to the next is made by separation in time.

    Do you know of any method that permits to analyze all the echoes at the same time (Superposition), so that a continuous image could be formed? Does an array of emitters permit a different approach? And a small frequency sweep?

    Best regards,
    João Carvalho

     
  4. magiciant

    August 20, 2014 at 7:31 pm

    “Do you know of any method that permits to analyze all the echoes at the same time (Superposition), so that a continuous image could be formed? Does an array of emitters permit a different approach? And a small frequency sweep?”
    I know at least 3 technology they use in telecom: FDMA, TDMA, CDMA. Here is no difference, to get information about an object, there must be a difference in frequency, time or code. Probably, code division isn’t applicable , as we have a “passive-unknown” object identification. But other two are beam forming (TDMA) and freq. variation(FDMA).

    I already describe limitations of the project on first VTS page. Radar with only one transmitter has no means to separate two objects, that located on the same spherical surface. Wikipedia may explains it better than me, but IMHO it’s obvious, as two echo would overlap. I get this from my secondary school physic lessons.
    “Thickness” of the surface defined by sampling rate of the ADC.
    The easiest way (cheapest) would be not to build full beam forming array, or introduce second sets of the sensors operated on another frequency (60 kHz, or 200kHz for example, small variation isn’t gonna to work), but use 3 more transmitters I still have on the board. Than I ‘d have 4 spherical surfaces “offset-ed”, and two object that get on same surface #1, may fall separately on #2 , #3 or #4 . Disadvantage of this approach, is reduced update frame rate by /4 and more complexity to the code, that would run cross pattern differentiation between 4 “images”.

     

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