Please Help ME!! -- RF Child Tracking System

Discussion in 'Wireless & RF Design' started by Hafizuddin Halim, Dec 3, 2014.

  1. Hafizuddin Halim

    Thread Starter New Member

    Dec 3, 2014
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    anyone can help me with my final projects??
    I have several problem with my FYP, before that i tell you about my project. My project is using RF transmitter and receiver 315Mhz. My plan is i want to make multiple transmitter connect to 1 receiver. I'm using 16f877a microcontroller

    the problems that i want to ask is:
    1. Does the transmitter and receiver need a proper circuit or just the devices alone?
    2. is it possible to use multiple transmitter with 1 receiver?

    I also attached my block diagram for this project. I hope someone can understand my diagram.
    Please someone help me ASAP. I to finish this fast:):):):)
     
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  2. wmodavis

    Well-Known Member

    Oct 23, 2010
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    "the problems that i want to ask is:
    1. Does the transmitter and receiver need a proper circuit or just the devices alone?
    2. is it possible to use multiple transmitter with 1 receiver?"

    1. - In general transmitters are electronic devices and therefore do need a 'proper circuit', whatever a 'proper circuit' is. These devices certainly need to be implemented from circuits that work and are compatible with other. But please clearly explain what you mean by 'proper circuit' and 'just devices alone'. It would help immensely if you could clearly explain what you mean.

    2. - Yes but with some restrictions.
     
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  3. Hafizuddin Halim

    Thread Starter New Member

    Dec 3, 2014
    6
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    Thank for your reply.

    1. About the 'proper circuit' and 'just device alone'. For example i want to connect receiver to PIC pin output. So, my understanding is I want to put the receiver to the output pin alone. But, when I go back to shop where i buy that receiver he said that before i connect to PIC the receiver must made in a circuit or it will be not functioning.(I hope you understand because i suck at explaining thing. My bad.). My PIC circuit design is connect with LCD display for displaying with one of the tag that out of the coverage.

    2. What are the restrictions. I hope you can tell me.

    I attached my circuit drawing. Sorry i ask many simple question because i'm still beginner.

    Apis
     
  4. Papabravo

    Expert

    Feb 24, 2006
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    You cannot have two or more transmitters talking at the same time. They will interfere with each other and the receiver will probably not be able to hear any of them
     
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  5. Hafizuddin Halim

    Thread Starter New Member

    Dec 3, 2014
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  6. Hafizuddin Halim

    Thread Starter New Member

    Dec 3, 2014
    6
    2
    Hmmm..
    Okay thank for you reply. I know transmitter and receiver is a pair and cannot be interfere. Just wanna asking if it possible or not. :)

    Apis
     
  7. wmodavis

    Well-Known Member

    Oct 23, 2010
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    150
    As papa says one of those restrictions I was referring is that of timing. A scanning receiver would allow reception from multiple receivers but in a sequenced fashion, I.e. Not at the same time. And to prevent interference independent frequencies would likely be necessary.

    And Haf if you cannot explain then how can we answer? We can guess at what you mean and are trying to explain but no guarantee our guesses and your needs will match up in a way that will be helpful to you. I suggest you probe for more detail from the guy at the receiver shop.

    I am very confused why you would connect the receiver to the PIC output. That would imply you are trying to control the receiver using a PIC output pin.
     
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  8. Hafizuddin Halim

    Thread Starter New Member

    Dec 3, 2014
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    Sorry that i have confused you :(
    Just another simple question. How can i control the timing and what i understand now that i just need to control the timing at transmitter. Am i right?
    I'm gonna go to that shop again.
    Thank you for your help

    Apis
     
  9. alfacliff

    Well-Known Member

    Dec 13, 2013
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    if you added a reciever to each transmitter, and had a protacal like packet running, so that each transmitter would listen befrore transmitting to prevent colisions, it would work, but more compicated. and the recieve modules available at 315 mhz are usually regenerative recievers with very broad bandwidth.
     
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  10. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
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    Just have each transmitter send a short transmission at a periodic interval which is slightly different for each transmitter. If the transmissions are each short duration, the probability of a collision (where two transmitters are keyed simultaneously) is vanishingly small. Since you likely are willing to miss a transmission or two before alarming that a kid is out of range, then an occasional collision wont matter.

    Those 315/433MHz receiver/transmitter pairs can be bought with and without a built-in encoder/decoder chip. I would buy the ones with the built-in decoder (click on this link), and use the decoder to determine which of several transmitters sent the message... You would use one receiver with multiple transmitters. The RF frequency is the same for all transmitters, the decoding that comes from the receiver is what tells you which transmitter.
     
    Last edited: Dec 3, 2014
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  11. Hafizuddin Halim

    Thread Starter New Member

    Dec 3, 2014
    6
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    owh i see..
    Anyways thank for the information. i'll try find that. :D
    I glad that i post here..hehe

    If i have any question i will ask sometimes...
    YNWA
     
  12. WBahn

    Moderator

    Mar 31, 2012
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    The exception being if you use Concurrent Code Spread Spectrum, which is beyond where you are at right now. So if you want to use multiple transmitters you will need to implement some time of medium access control (MAC) scheme, which is almost certainly also beyond you at this point unless you purchase transmitters and receivers that already implement this internally.
     
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  13. WBahn

    Moderator

    Mar 31, 2012
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    Since you aren't telling use what your transmitter and receiver are, we have no idea how much additional circuitry you would need.

    If this is your final year project, then you really should still be a beginner -- supposedly this is the final project to demonstrate that you are NOT still a beginner, that you are, in fact, ready to take on the duties of a full-fledged entry-level engineer.
     
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