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need help about Ultrasonic Range Finder

Discussion in 'Electronics Homework Help' started by jameschia, Jan 18, 2012.

  1. jameschia

    jameschia

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    Oct 18, 2011
    I am currently working on my final year project and my project is to build a ultrasonic range finder. I am now in troubleshooting stage and i fail it fix it after 2 month. just duno what is going wrong. does any one have some reliable source of project so that i can finish it by the death line. ur help will be appreciated.
     
  2. OLIVE2222

    OLIVE2222

    690
    25
    Oct 2, 2011
    Hi jameschia,

    Please post schematics (and maybe pictures) and tell what is working and what doesn't.

    Olivier
     
  3. jameschia

    jameschia

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    Oct 18, 2011
    [​IMG]
     
  4. jameschia

    jameschia

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    0
    Oct 18, 2011
    i cant find any way to upload my schematic here, pls refer it at
    "http://www.facebook.com/photo.php?f...116278552937.162413.1443669992&type=3&theater"

    The LM358 before CD4011 is use to detect the ultrasonic wave form and change it to 7V DC voltage.
    CD4011 is the holding circuit of detected signal. SR ( Set and Reset ) flip-flop is
    used. The detector is made to be not operate in the constant time (1.5 milliseconds)
    after sending out a transmission pulse to prevent from the wrong detection which is
    due to the influence of the transmission pulse. This operation is controlled with the
    software of PIC.
    But the problem is that there is no connection between either PIC or CD4011 with the transmitter circuit.
    Therefore, I do not know how to get the time when is the ultrasonic wave transmitted, and i am stuck at there and duno how to proceed on. any idea?
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Sorry, I don't do facebook.

    Can you post the image somewhere else (imagebucket?)
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    OK, presumably this is your design.

    Tell me how it's supposed to work.

    Have you just discovered there is no connection between the transmitter and the rest of the circuitry, or is that how you designed it? I can imagine a reason to do it that way, but surely you know *why* you did it?

    Did you write the software? How is it supposed to work?
     
  7. jameschia

    jameschia

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    Oct 18, 2011
    actually i just follow others thesis and i just follow what written in the thesis.
    but i am wondering on something in which the ultrasonic range finder function by determine time travel of ultrasonic sound to get the distance. but there is no way for the PIC to know when is the signal being transmitted, and the time travel as well. so this is what i am confusing.
    i not yet write the software because of this logic problem.
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Can't it sense the original (transmitted) pulse *and* the echo?
     
  9. jameschia

    jameschia

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    Oct 18, 2011
    According to my understanding, it will make the circuit ignore all signal input including reflected wave and echo for a period of time.
    Therefore, there will be a minimum distance to operate.
    For example, if the period is 1 milisecond, then the minimum distance will be
    340*1*10^-3 / 2 = 17cm.
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    OK, fine, but is there anything that will make it deaf to the pulse generated by the transmitter?

    (hint: There is no connection between the transmitter and the receiver/logic to do this)
     
  11. jameschia

    jameschia

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    Oct 18, 2011
    the thing that i can use to make it deaf to the pulse which is the signal generated by PIC *I think*.
    because the transmitter will only generate pulses for 1 milliseconds and stop for 65 milliseconds because of the first timer 555 and it will keep looping for that cycle.
    so I may use the on pulses generated by 1st timer 555 to some how trigger something of PIC to give a signal for the CD4011 to deaf to the pulses. this is my basic concept for the modification that i can do. means i have to link transmitter circuit to the PIC but i do not know will it work or nt.
     
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    But the PIC has no connection to the transmitter?

    It can only deafen the receiver after the receiver (which is connected to the PIC) hears something.

    Wouldn't it make sense that the PIC first hears the transmitted pulse, then shuts down the receiver for a short while before listening for the echo?
     
  13. jameschia

    jameschia

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    Oct 18, 2011
    http://www.imagebucket.net/bucket/is.php?i=10386&img=321.jpg

    this is the circuit of CD4011 part which will deafen the device.
    According to the circuit, the output of last NAND gate which is "leg 11" will always be off if the PIC do not provide voltage to "leg 8 and leg 6".
    therefore, as you say it can be both way either make the PIC hears pulse, then shut down the reciever; or shut down the receiver for a period then only turn on it.
    But the problem is how we going to know the time travel of ultrasonic wave since we do not know when is the wave being transmitted.
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Of course you will. The receiver will pick it up!

    The real question is how (or can) you determine whether the pulse you detect is the transmitter or the echo.

    An easy way is to connect one of the 555s to the PIC. But presumably the designer of this circuit didn't, and also presumably this wasn't an oversight.
     
  15. jameschia

    jameschia

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    Oct 18, 2011
    I don't think it can. That why it will shut down the receiver for a constant period.
    I got an idea, because the transmitted wave is trigger by a pulse of first timer 555 and I will use the pulse to tell the PIC the time that pulse being transmitted. I think it might work in this way.
     
  16. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    You don't understand why the receiver is shut down.

    Think about it some more.

    Sure, you can link the transmitter to the PIC, but I will tell you now that the circuit will most certainly "hear" the transmitted pulse. What is there in the circuit now to prevent it? (hint: nothing)
     
  17. jameschia

    jameschia

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    Oct 18, 2011
    I have no idea about it also. so any suggestion? or should I remove the CD4011B?
     
    Last edited: Jan 20, 2012
  18. jameschia

    jameschia

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    Oct 18, 2011
    http://www.imagebucket.net/bucket/is.php?i=10387&img=432.jpg

    I found this flow chart in the thesis that I refer.
    It will only turn on the receiver once the pulse being transmitted, and I think the CD4011B is the device to turn on receiver.
    And if I want to do in this way, for sure I will need to create a connection between transmitter circuit with PIC.
     
  19. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    That flowchart assumes there is a connection between the transmitter and the PIC, and ignores any time delay.

    As it is currently wired, you can have the receiver turned on until you hear a sound, then you turn it off for a millisecond(?) then turn it on to wait for another, then turn it off for a millisecond, then turn it back on and wait for a sound, and so on...

    So what do you hear? You hear transmitted pulse, echo, transmitted pulse, echo, ...

    If you time the delay between hearing the 2 sounds, you can calculate distance.

    However, you need to determine which is the transmitted pulse so that you can determine which delay to convert to a distance.

    Maybe there is a way to do that. If not, you need another way to determine either which pulse is the transmitter, or when the transmitter sent the pulse. Each method may give slightly different results, and one may be more valid than the other.
     
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