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radio frequency circuit design

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

  1. bananasiong

    bananasiong New Member

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    i'm now doing my final project. i need to attach a radio frequency circuit to my robot. i couldn't find any circuit about that. i need only the transmitter send a pulse, and the receiver just receive it and response to it. can any one help me??
     
  2. akg

    akg New Member

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    search for Fm transmitter and receiver ckt
     
  3. bananasiong

    bananasiong New Member

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    u mean search from the foeum of eletro-tech-online??
    is it necessary for me to use fm?? or am??
     
  4. dave

    Dave New Member

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  5. akg

    akg New Member

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    Google or ETO , both will help
     
  6. stevez

    stevez Active Member

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    Schematics and kits for relatively simple transmitters are abundant for the FM broadcast bands. That might explain the recommendation. I see a lot of activity in this forum regarding the 433 mHz modules (transmitter and receiver) that are fairly common and inexpensive. Much of the hard work is done for you but that may not be allowed by your instructor. You also need to consider the rules and regulations that apply to your location. Your instructor may or may not expect you to comply.

    If you have to build everything yourself give some consideration to lower frequencies such as AM broadcast. At higher frequencies keeping the transmitter and receiver on the same frequency will be a challenge with relatively simple circuits. More complex designs are out there however they can be a challenge to construct.

    Lots of choices here. Share some of the rules with us. Maybe you are allowed to use a receiver that you have around - that would simplify things to a great degree.
     
  7. bananasiong

    bananasiong New Member

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    what i need is, the distance between the antenna of tx and rx should be very close to get connection. but i can't use ir, because i'm using my robot in dirty environment. the receiver is inside the robot, when the robot goes near to the tx antenna (less than 10cm if possible), once it receives the rf, it will change direction and so on. the rest is almost okay, my problem now is the rf circuit.
     

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  8. akg

    akg New Member

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    in this case , u wont need the txs described above.

    since the "ant" encircles the robot, just pass a low/medium freq current thru that line at low voltage(need to be experimented) , the robot shld tune into that freq .
     
  9. bananasiong

    bananasiong New Member

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    oh!! thanks.. but, i don't know how to construct low frequency tx and rx as well.. can u show me a simple circuit?? i can't find the circuit from the net also.. thanks
     
  10. akg

    akg New Member

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    u didn't find anything from net .. :shock: :roll: .. ur app doesn't need freq stability , use a 555 osc ...
     
  11. bananasiong

    bananasiong New Member

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    use a 555 timer?? how it transmit the signal?? and how about the receiving part?? sorry.. i realy need helps..
     
  12. Russlk

    Russlk New Member

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    Try this out. You may have to tweak the frequency and antenna current.
     

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  13. mstechca

    mstechca New Member

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    Why do you care?
    that last circuit is good, except that the following should be done:

    Instead of connecting the output of the 555 to a pull-down resistor, do this:

    Connect the output of the 555 to one end of a large value capacitor. The other end is connected to a grounded tank circuit. Stick the antenna at the point where the two capacitors are connected (one being in the tank circuit).
    Set the values in the tank circuit so that its resonant frequency is the frequency you want to transmit on.

    I do advise the coupling capacitor in order to prevent the output from shorting to the ground via the inductor.
     
  14. bananasiong

    bananasiong New Member

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    "connect the o/p of the 555 to one end of a large value capacitor?, then how about the resistor between the o/p and the antenna? ignore it? and.. what is tank circuit?.. for the receiving part.. what is the triangle thing? and what is the mouser? sorry.. i really don't understand.. please show me the correct circuit design... thank you so much..
     
  15. akg

    akg New Member

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    i don't think these modification have any advantage in the present context , apart from adding complexity .
     
  16. akg

    akg New Member

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    it is a heart of an LC oscillator , where the oscillations start.
    the 'triangle' thing is an 'operational amplifier' or simply opamp
    and mouser is a company , the number shown is their catalog number for that part.
     
  17. mstechca

    mstechca New Member

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    Why do you care?
    I have included an attachment that shows the circuit. It should be easy to hook up.

    And the advantage with this circuit is that the output is actually going someplace useful!

    All that the current output is doing (without making any modifications) is giving itself to the resistor. and what I like to know is, other than generating heat, Why would anyone (with experience) want to just connect a grounded resistor to the output, and nothing else?

    anyways, the tank circuit in my diagram is the inductor (the bottom-left-most component) and the capacitor (two T's with their heads almost touching each other) next to it. The coupling capacitor is the remaining component.

    I suggest using a large value capacitor so that a large portion of the signal can be passed on. I suggest a 0.1uF capacitor. Capacitors do block DC, so there is NO chance of a short circuit.

    Now on to the tank. The goal is to pick a low inductor, and a low capacitor value. and use the following equation to determine the resonant frequency (the frequency you will will be transmitting on).

    f = 1/(2*pi*sqr(l*c))

    pi is equal to whatever appears on your calculator after you press the "pi" button. sqr means "square root of".
     

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  18. bananasiong

    bananasiong New Member

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    oh i see! thanks a lot! so just ignore the word mouser... just get a same value inductor, am i right? from the transmitting part, the sentence "use a 10k pot to adjust frequency".. is it variable resistor? there is no variable resistor.. and.. for the receiving part, how do i know if i get the signal? don't we need to tune at the output??

    thanks for answering my question..
     
  19. bananasiong

    bananasiong New Member

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    u mean.. a large value capacitor, which one? both or only one? the one parallel with the inductor? or the one straight from output?? then how about the value of the inductor?? thanks a lot...
     
  20. Roff

    Roff Well-Known Member

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    Mstechca, you are an interesting character. It apparently never crossed your mind that Russ has been around the block a few more times than you, and might know something you don't. I don't want to imply that you know nothing, but you might want to consider that Russ is a retired engineer, while you are a hobbyist still struggling to understand the fundamentals of electronics. It would behoove you to ask how his circuit works, instead of proclaiming that it doesn't.
    Russ's circuit is setting up a alternating current in the loop. This causes the loop to radiate an electromagnetic field. The receiver will pick up that field when it gets close to the loop. More current will be launched into that loop (which is an inductor, BTW) his way than you will ever get by trying drive one end of it off a tank circuit.
    One way to improve the efficiency might be to resonate the loop (possibly a multi-turn loop) with a capacitor, and drive it with a transistor operated in class C mode.
     
  21. audioguru

    audioguru Well-Known Member Most Helpful Member

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    A tank circuit is a high impedance parallel resonant circuit. It should be driven from the very high impedance of the collector of a transistor, not the very low impedance output of a 555 where it won't do anything.
     

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