Need help with Wireless Doorbell: inductors!

Discussion in 'The Projects Forum' started by polygriff, May 20, 2011.

  1. polygriff

    Thread Starter New Member

    May 20, 2011
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    Good day everyone!

    I'm currently working on a wireless doorbell (no crystal) project. I am using this schematic from http://www.google.com.ph/imgres?img...&ndsp=16&ved=1t:429,r:14,s:0&biw=1366&bih=643

    i got lost on the tank circuit (the one with the bold wires?lol). it says it should be a one turn coil but i have no idea about the diameter of the coil (actually I'm just a newbie for RF stuffs, so please bear with me).
    Another thing is that I can't find available 15uH inductors around, so I wonder if 18uH will be fine.
    Thank you very much! :]
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The value of the 15μH is not critical in that circuit.
    It is only used to feed the "thick" wire coil circuit.

    The size of the "thick" wire is critical for the frequency.
    Where is the description of the "thick" wire size?
    I only see a drawing.

    Bertus
     
  3. polygriff

    Thread Starter New Member

    May 20, 2011
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  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The only sizze I see is at the part where they show how to add an antenna;

    [​IMG]

    The "thick" wire seems to be a part of the PCB that is NOT shown.

    Bertus
     
  5. polygriff

    Thread Starter New Member

    May 20, 2011
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    i see. but should it work if i just included it in the pcb?i mean, do i disregard that 'thickness'?
     
  6. CDRIVE

    Senior Member

    Jul 1, 2008
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    I don't want to be a killjoy here but the output tank 'L' is indeed microstrip technology. The authors give little insight into properly making this and 303MHz isn't easy to play with... especially for a novice. Lacking the instrumentation, to know that you have generated this frequency, this thread could stretch into the year 2020. :D

    Then comes the receiver, which will be even more difficult!
     
  7. DickCappels

    Moderator

    Aug 21, 2008
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    [​IMG]
    The think "U" shaped trace is the single turn inductor. The two pair of holes are for the resonating capacitor. Try about a 2 cm length for the inductor. The adjustable resonating capacitor should be able to get you to the right frequency (about 330 MHz). Note: If you are planning to use this in the United States, you would be well off to use a SAW resonator to set the frequency to make sure you are within the allotted band for RF remote control (reading of Part 15, title 47 of the CFR is left as an exercise for the student).

    Just for reference, here is a 330 MHz transmitter made without a SAW resonator and will give you an idea of the dimensions:
    http://cappels.org/dproj/330MHz_Rem...ntrol_Simulationg_PT2264_with_ATTINY2313.html
     
  8. polygriff

    Thread Starter New Member

    May 20, 2011
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    does that mean that single turned coil is just a thickened clad if i'm going to etch it??can i use the one where they included the antenna???
     
  9. DickCappels

    Moderator

    Aug 21, 2008
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    I'm not sure what you mean by "thick"; if you mean the "wide" trace, then yes. Yes, you can include the antenna, but I have not noticed a pronounced effect by including the antenna. The printed circuit inductor is an antenna. I suggest leaving out the extra "antenna" trace on your first attempt, just to make things simpler. You could add the antenna as a small bit of wire later if you want to experiment with it.
     
  10. polygriff

    Thread Starter New Member

    May 20, 2011
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    can i add another question? it's about the variable coil on the receiver side. i bought a 3-turn coil (i can't find a variable coil with 2.5 turns). I also have a variable coil which was taken from my AM receiver project (I don't know anything about it, except it has 5 legs). i wonder if it could still work when i use either?

    ..can i also replace the 82uH inductor with 100uH? I've got a very limited resources from where i am..and i badly need to make this work.
     
  11. DickCappels

    Moderator

    Aug 21, 2008
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    If your adjustable inductor was not designed for use in this frequency range, it probably will not work as you hope. The characteristics of the core are very important. I suggest that you consider a printed circuit inductor just the same as the one in the transmitter and use an adjustable capacitor to make it resonate at the desired frequency.

    I don't see the 82 uH inductor, but as with Bertus's earlier comment, at these frequencies, a few uH is the same as many uH, so (without understanding exactly what you want to do), you can probably substitute the 100 uh. If you would like a more certain answer, please explain where the 82 uH is used.
     
  12. polygriff

    Thread Starter New Member

    May 20, 2011
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    sir, i came up with this design, would you mind checking it for me? it's the transmitter side.


    [​IMG]
     
  13. DickCappels

    Moderator

    Aug 21, 2008
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    There is not enough information to allow a check. Component placement? What is the scale?
     
  14. polygriff

    Thread Starter New Member

    May 20, 2011
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    [​IMG]

    the width of the coil i made is about 5mm..
     
  15. DickCappels

    Moderator

    Aug 21, 2008
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    It might. I suggest that you move the capacitors to the end of the inductor,where C2 and Q3 connect, otherwise, you will have a funny circuit with at least two resonant frequencies.

    If I am not mistaken, the other end of the capacitor connected to the emitter of Q3 should connect to the collector, not the base.

    I did not look at the Q1 and Q2 circuits.
     
  16. polygriff

    Thread Starter New Member

    May 20, 2011
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    okay, now i don't know how to know if it's working...so i leave it for now..

    my receiver circuit now has the problem..the problem is that the 3v supply could already trigger the output, therefore making a sound everytime..
     
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