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Parking Car ElectroMagnetic Sensor

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by giusepped, Oct 31, 2007.

  1. giusepped

    giusepped New Member

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    I saw that there is a new type of proximity sensor for parking assistance.

    I forgot almost everything of basic physics, and I am curious to know if somebody can explain how this kind of circuit runs.
    http://www.carparkingsensordirect.com
    Basically, the website says that there is an antenna on the back of the van, a adhesive antenna made of aluminium. The magnetic field varies when a wall or an object enters in the space occupied by the magnetic field.

    But I we can measure the magnetic field?
    Any help appreciated
    G
     
  2. ssylee

    ssylee New Member

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    You can measure the magnetic field by using a Hall effect proximity sensor.
     
  3. giusepped

    giusepped New Member

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    To ssylee.

    Yes I know that. But they do all with the same "antenna". Did you take a look at the website I attached?
    Thanks
     
  4. dave miyares

    Dave New Member

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  5. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    The site doesn't really tell how it works. I doubt it is magnetic. It may be capacitative. Search on capaciflector, which has a detection range of about what is claimed. John

    Edit: Here are some references from a NASA report. I am reluctant to put the whole report, as it is about 500K.
    “Capaciflector Technology Applications,” [Online Document], 2003 Dec 10, [cited 2005 Feb 01], Available HTTP: http://capaciflector.gsfc.nasa.gov/applications.html
    “John Vranish, Electrical Engineer, GODDARD SPACE FLIGHT CENTER,” [Online Document], 1998, [cited 2005 Feb 01], Available HTTP: http://academy.gsfc.nasa.gov/1998/html/john_vranish.html
    “The "Capaciflector" Proximity Sensor,” [Online Document], Date Unknown, [cited 2005 Feb 01], Available HTTP: http://www-cdr.stanford.edu/Touch/previous_projects/capaciflector/capaciflector.html
    “Capaciflector Technology Description,” [Online Document], 2003 Dec 10, [cited 2005 Feb 01], Available HTTP: http://capaciflector.gsfc.nasa.gov/description.html
    “Capaciflector Technology Benefits,” [Online Document], 2003 Dec 10, [cited 2005 Feb 01], Available HTTP: http://capaciflector.gsfc.nasa.gov/benefits.html
     
    Last edited: Nov 1, 2007
  6. giusepped

    giusepped New Member

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    Thank you

    Thank you very much,
    I did not know at all about it.
    I will try to build some prototype and I will tell you my results!
    G
     
  7. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    I built a simple one about a year ago with a sensor that was about 7 cm long and had a detection range for my hand of 12 to 14 inches. The key to making it work, which is even mentioned in the advertisement, is to standardize or calibrate whenever you first turn it on. Good luck. John
     
  8. dave miyares

    Dave New Member

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  9. giusepped

    giusepped New Member

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    However, if we put an inductance as sensor the effect should be the same.
    Also coils change their inductance if an object is near.
    A long string of aluminium could be a good inductor?
    G
     
  10. giusepped

    giusepped New Member

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    No, I mistaken. The inductance changes if a metal object is close!
    G
     
  11. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    A frequent contributor to this forum, Chemelec, has designed a nice, inductance-based detector for cars. See:

    http://www3.telus.net/chemelec/Projects/Loop-Detector/Loop-Detector.htm

    However, from my understanding of what you want to do, I don't think that is the answer. For detecting any object at distances of 15 cm or more, I think your best chance is with capacitance, ultrasound, or reflected IR/light.
    John
     
  12. giusepped

    giusepped New Member

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    Capaciflector

    I think to realize the sensor by using a capacitive sensor and a Wien Oscillator.
    Anyone of you have some suggestions for buildings a capacflector?
    G
     
  13. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    For the capaciflector, see the references already given or search on the term. If you search on patents, check on John Vranish as an inventor. I found two basic approaches to it, which in the NASA reports were known by the developer's name. One is referred to as Dr. Edward Cheung's design and a very similar design by Niels Smaby (also referred to as the Stanford design) were simple and worked for me. The other design by Vranish is a little more complicated and uses frequency sweep. The simplest design was based on an op-amp (LT1057) set up as an oscillator with the capacitative sensor on the inverting input. It is shown in the NASA reports.

    You can also check out a series of devices form Analog Microelectronics for capacitative sensors and measurement. See:
    http://www.alldatasheet.com/datasheet-pdf/pdf/197607/AME/CAV414.html

    John

    Edit: I found this schematic of one version I made. Note: JP1 is labeled for the different capaciflector plates. The LM567 was used to detect a tone shift (i.e., object) which was the signal to other parts of the circuit.
     

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    Last edited: Nov 7, 2007
  14. giusepped

    giusepped New Member

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    I see, thank you.
    But I mean if you have some suggestion on how to build practically the sensors, not the circuitry.G
     
  15. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    The NASA publications include a student report that has a step by step procedure, including dimensions and PCB layouts, for building an obstacle avoiding robot. For the sensor I built, I just used PCB material for the conductive surfaces and clear packing tape for the dielectric layers.

    I can't be much more definite than that. The student report I referenced was done at Michigan State University (http://www.egr.msu.edu/classes/ece480/goodman/), but that site has been updated to 2007. The report you want is from November, 2004. I believe that report is still available on the NASA links. You might try to contact Prof. Goodman (the faculty advisor at MSU) directly; however, I would suggest that first you get on the internet and search the references already provided. Second, you need define better exactly what you want to do. John
     
  16. giusepped

    giusepped New Member

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    Ok, I'll take a look.
    However, my original goal is to build a simple proximity sensor for my car.
    I think to use the relaxation oscillator with its capacitor coupled with the sensor.
    The sensor should be put in the baggage van of the car and should be small.
    I think to make a long strip of aluminium and use paper as dieletric.
    G
     
  17. giusepped

    giusepped New Member

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    I tried to connect to urls but they seem broken.
    May you attach a pic of your sensor?
    G
     
  18. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    Have you searched on capaciflector? I did and got three pages of hits that included patents, the Stanford work, and the MSU work. Here is one current (2007) hit from MSU:
    http://www.egr.msu.edu/classes/ece480/goodman/spring/group02/

    I did not take any pictures of the capaciflector sensor built.
    John

    Edit: The link works from this page.
     
  19. giusepped

    giusepped New Member

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    Patent pdf

    I found the original article on capaciflector on freepatentsonline.com
    I attach it
     

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  20. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    Yes, the Vranish design is quite a bit more complicated than the other designs I have mentioned. I would suggest going with the simpler designs. By using frequency scanning, Vranish could determine not only the presence of an object, but something about its composition. I suspect you do not need the latter just to start your application. John
     
  21. giusepped

    giusepped New Member

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    Problem with the oscillator

    Why the following oscilaltor does not oscillate?
    If I put single supply voltage the oscilator does not oscillate, and If I put
    double supply voltage it oscilaltes.....
    Please help
     

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  22. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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