looking to build ultrasonic motion detector

Discussion in 'The Projects Forum' started by Avanti, Feb 25, 2008.

  1. Avanti

    Thread Starter New Member

    Feb 15, 2008
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    Does anyone have an idea where I can find a schematic or tutorial to build an ultrasonic motion detector? I see many circuits and premade sensors available, but my problem is they all have a long sensing distance. I need a maximum of 8" sensing distance. I want it to have an output to operate a transistor switch triggering a 555 timer. Can the sensing distance be made adjustable on ultrasonics.
    I'm using infrared for the sensor now, but would like to experiment with ultrasonics. I think it might be a more reliable detector with less false triggers. Any help would be greatly appreciated.
     
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    There are commercial ultrasonic detector units that work to a fraction of an inch. Check out Hyde Park Sensors (http://www.hpsensors.com). They attain that range by operating at something like 500KHz.

    You say a maximum of 8"for detection distance. What is the minimum distance you need (i.e., the range)? Are you trying to detect motion per se or just the presence or absence of an object within a certain range? If it's the latter, you may be better off sticking with modulated IR and using noise cancellation with a microcontroller program. If you are up to that, let us know and I will dig up some references and post a schematic. John
     
  3. Avanti

    Thread Starter New Member

    Feb 15, 2008
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    I am just looking to detect presence of an object. Minimum distance I would be working with is 2". I am presently using a Sharp GP2D120 IR sensor. The detection distance is fine, but I get false detections every now and then. It is being used indoors and I have tried pointing it in different directions and in total darkness. I'm not sure what is tripping it. If I can get the present sensor close to 100% reliability then I would much rather stay with it. Any suggestions would be appreciated.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    Do you have 0.1uF ceramic or tantalum bypass capacitors on all of your ICs power/ground pins? If not, that's a huge source of noise.

    If your wires to your battery are of any length, you should have an electrolytic cap on the board where the wires connect.
     
  5. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Here is a link to noise correction using the 12F series PIC.

    http://users.frii.com/dlc/robotics/projects/botproj.htm

    Scroll to the 12C508 project. There are also useful links therein to the Dallas group.

    The best part of the project is the error correction concept. The code is for a 12C/F series PIC, but is easily adapted to other versions. The schematic and code are attached. The code was in asm but was converted to txt for posting.

    I have been using a modified version to detect movement of a 3/16 inch wire that is about an inch or two from the detector (see picture). The application has been outdoors in bright sunlight and flawless. It will also work with your finger.

    John
     
  6. hgmjr

    Moderator

    Jan 28, 2005
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    If you can provide a schematic of the circuit you are currently using that would make it easier for us to assist you.

    hgmjr
     
  7. danny520

    New Member

    Feb 27, 2008
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    I think u can go to wikipedia or some other professional tech site such as cnet.com or about.com to find ur professional issue.::rolleyes:
    And i've got my Infrared Motion Sensor Wireless Alarm Home Security System three days ago. But i think it may be similar with ur devices on technology.:D But it seems i'm wrong.LOL
     
  8. Avanti

    Thread Starter New Member

    Feb 15, 2008
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    I've attached a schematic of my circuit. Sorry for the crudeness of it. Hand drawn and I'm new at this so I hope I got all the symbols correct. I've also attached the data sheet for the sensor I'm using. Any help would be really appreciated. Or any suggestions on a better circuit to use. A circuit using a programmed chip was mentioned. Is that something a newby with no programming experience could learn to do? I like a good challenge, but also realize the limitations of my experience, or lack there of. Thanks.
     
  9. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    It looks like you have a modulated IR, which can be considered as a first step to avoid false signals. Those have been a problem with your current circuit and component layout. Two obvious solutions are error correction, as in the example I posted, and using a coded signal, such as one uses with a TV remote. There are some nice coder/decoder chips out there. I have used the Holtek 12 series (see: www. rentron.com), Microchip HCS101, and Motorola 145026/7/8 series. There are probably some new and better ones available now. All you have to do is set jumpers for the encoder and have the same jumper code set for the decoder. They all work.

    However, after a little bit of study, I tried the PIC 16F628 microcontroller, got LEDs to flash, then did the program I attached above. Once having done it that way, you will realize how easy the MCU is to use and will probably not go back to the individual chips. I haven't.

    At this point, you need to decide whether you want to continue with the simple modulated IRED, the discrete chips, or an MCU. In my experience, you can get pretty good reliability with the simple modulated IRED. You can improve its performance by using a tighter bandpass on the receiver and most important by adjusting the physical layout, using light shields, etc. Remember IR can pass though things that look solid. Black electrical tape and aluminum foil are pretty good blockers.

    John
     
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