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radio frequency circuit design

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by bananasiong, Mar 8, 2006.

  1. mstechca

    mstechca New Member

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    Why do you care?
    Now audioguru has explained why that circuit I think didnt work, works.

    I understand it before you told me about it. But the diagram showed me that the resistor is connected to ground. There is a BIG difference between an inductor symbol and a wire!

    I don't claim I'm perfect, but I have SOME knowledge. On a scale of 1 to 5 for knowledge, you might give me a 2. I give myself a 3.

    If garbage to you is helpful information to them, why not show it?
     
  2. Roff

    Roff Well-Known Member

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    Snort! :roll:
     
  3. mstechca

    mstechca New Member

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    Why do you care?
    :wink:
     
  4. dave

    Dave New Member

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  5. akg

    akg New Member

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    forgiven :)
    "probably u wont require an ant:(and it should work in ur case) , the coil will pick the freq. and , if u need connect it to pin 2 "
     
  6. bananasiong

    bananasiong New Member

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    u mean.. if i need an antenna for the receiver, just connect it from pin2?? thanks for ur forgiving ya..
     
  7. akg

    akg New Member

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    IF needed , most probably wont , since the underlying principle is induction.
     
  8. bananasiong

    bananasiong New Member

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    hi,

    these circuit can be said that almost completed, but i found another problem. when there is no signal, yes, the output is high, but there is a low in very short time (i used cro to measure), as shown in A.
    when there is signal, yes, i got square wave from the cro as shown in B.

    my problem is, my microcontroller will keep reading to the output of the receiver. if there is a low (0), it will response to it and turn. but if there is a low when there is no signal, and if the microcontroller "assume" that it detects the signal because of the short low, then it will turn without any signal.

    do u all get what i mean?
     

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  9. Roff

    Roff Well-Known Member

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    The random pulses are probably due to noise. You need to add some software filtering. Look for at least ten (or whatever) consecutive pulses before you qualify it as a command to turn.
     
  10. bananasiong

    bananasiong New Member

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    what is software filtering? is it a filter? i've tried to use a lpf to cut off the frequency which is higher than what i have calculated. but the noise is still there. unless i hold the other end of the transmitting "antenna" (using hand), the output has nice pulses.

    but when there is no signal, the short low is still there.
     
  11. Roff

    Roff Well-Known Member

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    I'll say it again:
    You have to incorporate this into your program in your microcontroller. You know what the pulse rate is. When you get a pulse, look to see if another one occurs one pulse time later. If it does, look again one pulse time later. Do this in a timed loop as many times as you think is necessary to qualify the receiver output as signal, and not just noise.
    There may be a much better algorithm that one of the other guys can suggest. This is just an idea to start you thinking. Or maybe it will work just fine. :roll:
     
  12. akg

    akg New Member

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    good to hear that it works :)
    for the noise problem , as ron suggested , that will be the cheapest solution .
    in ur micro start a 'window' timer when a pulse is received , and count the number of pulses received during the 'window' period, and u know what will be the count when an expected signal is received.
    btw , what freq u used.?
     
  13. bananasiong

    bananasiong New Member

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    i use the same as given, around 10KHz (using calculation). but from the cro, it shows around 330KHz. :roll:
     
  14. akg

    akg New Member

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    it couldn't be. check the value of r and c . also the cro settings
     
  15. bananasiong

    bananasiong New Member

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    yea.. i used a 1K for R1, 10K VR for R2 and 0.01uF for C. the 10K is set to around 7K. from calculation, it should be 10KHz right? but from the cro, it gave me around 330KHz (a long on time and a very short off time). i have tried both CRO and digital osciloscop, they gave the same results.

    when the 'receiver' detects the electromagnectic flux, the cro gave a nice square wave (on time and off time are almost the same). i used 10mH and 0.022uF.
     
  16. bananasiong

    bananasiong New Member

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    but i don't think the frequency give me problem, as long as it can detect the 'antenna', every will be fine. but my problem is, what i've mentioned before. when there is no signal, the output of the receiver give a very short off time. i think it's the op-amp's problem (just think!), shall i change another type of amplifier such as a BJT? as an amplifer.
     
  17. Roff

    Roff Well-Known Member

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    Do you understand how powerful a microcontroller is? Spend some time learning to program it. As we have told you, it is the answer to your noise problem. You could spend months farting around with different kinds of comparators (a comparator is not an op amp) and filtering schemes. Also, if you get your transmit and receive frequencies to match, you will get better noise rejection. If you want to learn from a project, one of the most important things you can do is understand why it doesn't work the way you think it should. We always learn more from our mistakes and failures than we do from our successes.
     
  18. bananasiong

    bananasiong New Member

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    yes sir!! :D i will troubleshoot to make it well. thanks a lot.
     
  19. bananasiong

    bananasiong New Member

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    i'm now using motorola 68HC11 E series (this is the only i can use and know how to use). i don't think it can be used perfectly if the receiver gives a short off when there is no signal. because my microcontroller keeps detecting the output of the receiver, if there is a '0', it will response to it and turn.
     
  20. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    It makes no difference what processor you use, if there's a spurious short '0' do as already advised and software filter it - basically don't respond unless the '0' lasts more than a certain time.
     
  21. bananasiong

    bananasiong New Member

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    yes, i do agree this one.. but i have only the basic knowledge of controlling this microcontroller.. so, i need time to figure it out.

    thanks for all your advises!! :D :D
     

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