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rf morse code

Discussion in 'Electronic Basics' started by Andrey Fedorov, Aug 17, 2003.

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  1. I'm a high school senior and I've gotten into basic robotics lately. I'd
    like to build two circuits with PIC microcontrollers: one that sends an
    rf signal, and one that recieves it. I have learned the basic
    input/output of the PIC, but I'm having trouble figuring out how I can
    transmit information from one circuit to another (via rf).

    I'd like to make two circuits that can communicate (make a LED flash)
    via rf... A friend told me that I can use Quartz Crystals. Another said
    that's very unlikely, a third said that he's not sure, but it may be
    possible... does anyone have any suggestions, or better: informational
    sources (web sites, tutorials?).

  2. You want to make a radio transmitter and a radio receiver. Your PIC will
    create the Morse code patterns and use them to key an oscillator, and this
    signal will get mixed with a carrier wave for AM, or you will use it to modulate
    the frequency of an RF oscillator for FM.
    The receive it, you need to use a small radio receiver and a phase locked
    loop to turn the audio tones back into on-off signals. As the PLL show lock or
    not, you will see ones and zeroes corresponding to the original code.
    Look up radio circuits. Google is sure to have many, but a library is a far
    better resource.


    Chip Shults
    My robotics, space and CGI web page -
  3. I was thinking maybe something simpler, like: i push button here, LED
    across the room lights up... or is that what you are descibing?
  4. Bengt

    Bengt Guest

    Maybe you should have a look at som simple ham projects? QRP
    transmitters and DC recievers.

    Here is one link:

    Another way is to read books such as ARRLs "Amateur handbook", there you
    find all you need to know about how to design and build radio equipment
    like that.

  5. thanks :)

    I've been getting bits and pieces to make sense for me...
    very basically: any electrical flow creates a magnetic field, crystals,
    because they vibrate, create a specific RF resonance. This resonance can
    be picked up by other crystals and translated into a slight voltage.
    What I'm going to try to do is set up two crystals: one to resonate and
    another to recieve the resonance which the PIC will pick up...

    where am i off?

  6. Andrey Fedorov wrote:

    ok, i'm probably oversimplifying... and it's 5am, i'm going to bed.

    thanks for all the advice!!!

    i'll check back tomorrow if anyone has any more suggestions :)
  7. Err..lets distinguish between *what* is required and methods to achieve
    what is required. You don't *need* a PLL. A PLL is simply *one* method
    of achieving a particular function. All one needs here is a radio
    receiver. Feeding the receivers audio into a comparator via a diode dc
    restorer is probable all that is required.

    Kevin Aylward
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
  8. Rich Webb

    Rich Webb Guest

    Morse isn't the easiest protocol to implement, although there are
    certainly examples of source code to encode/decode using Morse.

    Take a look at
    which is a pair of demo boards that might be interesting.

    Pick up a copy of Circuit Cellar or Nuts & Volts and browse through the
    adverts. There are quite a few RF modules available.

    Otherwise, google for some reference designs.
  9. There are lots of ways to transmit information. You could use infrared (like
    TV remote controls), or ultrasonic sound waves. If you are determined to use
    RF, you could buy boards to do it... look at

    for $30 US you can quickly get a system up and running. You'll have to
    figure out how to interface the PIC to the board, but that sounds like fun,
    eh? Note that transmission is one way, so you'll need two more cards to go
    both ways with this solution.

    Ultrasonics is also pretty good. You can get transducers at electronic

    There are circuits on the web for driving them. You can use the same
    transducers to send and receive with the proper circuit, but only half
    duplex. An LM567 chip will detect an oscillation at a programmed frequency,
    and give you a '1' signal when it sees it. You can generate the signal on
    the other side using the PIC to drive the transducer at the right frequency
    (actually, you'll need a driver chip, I don't think the PIC can generate
    much power from its ports.) You will also need to amplify the transducer

    There are also other cool things you can do with ultrasonic transducers; you
    can use them to detect the distance and direction to an object by sending a
    pulse, then using two of them and the speed of sound and a few simple
    calcuations... You can use them to detect motion by determining the change
    in intensity of reflections. You can also use them to scare away insects...

    Regards, and good luck!
    Bob Monsen
  10. thanks a ton.

    i found this link really useful also :)

    just a quick glance of what i'm shooting for:
    I started a robotics club at school this year and would like to make our
    first project a remote locker opener. ultimately, I'd like to have a
    solenoid coil insite the locker controlled by a pic which waits for a
    certain binary signal to open the lock.

    any suggestions?
  11. I think you could do this with ultrasonics, if there is an air vent in the
    locker. Amplify the output of the transducer, and feed the result into the
    LM567 chip. That will output a high signal if its receiving a signal
    (assuming its configured correctly. Look at the data sheet.) If you take
    that high signal, and use it to run a power mosfet or relay, you can get
    lots of current, which you can use to move the solenoid. Note that solenoids
    may take a fair amount of current to run, so you'll need a fairly big

    Take a look at this circuit: Detector/UltrasonicMotionDetector.pdf

    It has a transmitter circuit you could easily use, and amplifiers for the
    receiver. Modifying it to do what you want should be pretty easy. Instead of
    using a crystal, as specified, you could use the PIC to drive the

    With regards, to using radio for this, I bought a little toy car from radio
    shack for $10 (on sale) that contained a transmitter/receiver pair that
    would be perfect for your application (assuming, again, that the locker
    doesn't block the radio transmitter too much.) A button press on the
    transmitter transmits at about 40MHz, which is received by the little
    receiver card (which runs from a 6 volt battery array.) The output is a high
    signal on the card, which could be fed into a power driver for the solenoid
    like that described above. I don't know how much of the signal would be
    blocked by the locker. Maybe I'll try it out with my daughter's locker (she
    is starting HS in a few days.) Make it beep, and see if it gets through. I
    could try it with the fridge, I guess :)

    Another issue you might have is interference. I've noticed that with the car
    receiver, it occasionally triggers without a button press; probably ambient
    radio waves. However, if your locker occasionally unlocks on its own, that
    would be bad... :) I don't think it'll be as much of a problem with the
    ultrasonic scheme, since there aren't many sources of it that are 'pure'
    enough to trigger the 567.

    Sounds like a fun project, and not too hard to pull off. You should find a
    mentor someplace near you to help with obtaining the parts, etc. Maybe a
    teacher at your school?

    Bob Monsen
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