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one channel radio frequency help

Discussion in 'Electronic Design' started by robot guy, Apr 3, 2007.

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  1. robot guy

    robot guy Guest

    I could use some input on this subject. A while ago I used infared
    led's hooked up to a 555 to flash at a certain speed, I can't remember
    what speed it was but I then had some special little divice that when
    it saw an infared flashing at one specific givin speed it would either
    close a switch completing the circuit, I can't quite remember how I
    wired it but any way I'd like to do the same with a radio. What I want
    it to do is turn on and led first than move on to turning on ovens,
    unlocking cars etc...
    I have a good idea how to do it, just take a transmiter and pulse it
    at a certain speed with a 555 but how do I get my reciever to only
    regonize that certain speed, a filter, a tone detector? I could really
    use some input or websites to look at.
     
  2. Make it up from scratch again, just like you did the first time, as you
    seem to indicate[1]; and this time, if you're too drunk or zoned to
    remember, take notes. For that matter, take notes anyway.

    And always remember the first tenet of "State-Dependent Learning":
    "If you can't learn it while you're high, you can't learn it."

    And, just because I'm feeling frisky at this moment in spacetime, I
    feel like ripping off one of Uncle Jimbo's lines: "Kids, there's a
    time and a place for everything, and that's College!"

    Have Fun!
    Rich
    [1]: "A while ago I used infared led's hooked up to a 555 to flash at a
    certain speed ..."
    [1A]: "I can't quite remember how I wired it..."
     
  3. robot guy

    robot guy Guest

    Only problem is that the I don't know what was causing the device to
    only respond to a certaing rate of speed from the flashing led. It was
    all pre manufactured into a little sugur cube sized box.
     
  4. Luhan

    Luhan Guest

    I did something like this once to unlock my car and house by just
    walking up to them. It used a PIC for the sending unit banging out a
    very short code pulse about once a second and then going back to
    sleep.

    It worked great 'on the bench' and totally failed in any bright
    daylight.

    Luhan
    http://mondo-technology.com
     
  5. Look at garage door openers, they use coder (usually set with bank of
    swithes) in transmitter AND receiver. When those two codes match an
    action is performed. But you have to have different music for every item
    that you want to respond to your orders.

    Something to do.

    HTH

    Stanislaw
     
  6. Gary Tait

    Gary Tait Guest

    You had, likely, a typical IR reciever module from a VCR os the like. The
    simply detect the presence of an IR signal oscillating at around 40 Khz,
    and activate (pull to ground) the output pin at the presence of the 40Khz
    IR signal. Your 555 was blinking the IR LED at the set frequency for that
    module. A typical IR remote would modulate that carrier by turning it on
    and off in the data pattern the remote creates.

    RF remotes are similar, in that instead of a 40 Kz carrier on an IR LED,
    the data pattern is directly modulates the transmitter. In theory, you
    could do the the same, by gating an RF carrier, and detecting its presence,
    but that is less than ideal. You should encode it, and depending on the
    application, you should have a self error checking code.
     
  7. joseph2k

    joseph2k Guest

    If you can bother you can find chips that do both the transmit and receive
    functions for IR or RF remotes. They are typically marketed in transmit -
    receive pairs. There are usually inexpensive ceramic resonators to
    generate master clock frequencies for both parts.
     
  8. Gary Tait

    Gary Tait Guest

    Nowadays though, the system controller of the device being controlled
    decodes the data coming from the IR or RF receiver, rather than a
    standalone decoder IC.
     
  9. joseph2k

    joseph2k Guest

    I was talking about the transmitter and receiver IC's themselves. Even in
    my very old designs the decision on what actions to take were made by a
    micro that defined the application.
     
  10. Gary Tait

    Gary Tait Guest

    Well, for typical IR remotes, and basic non-secure RF remotes, they use
    more or less a complex logic device, or even a real low end micro. They
    directly provide a signal to drive an IR LED (through a drive
    transistor), or gate an RF transmitter, which is typically one or two
    trasnistors, a coil or SAW filter, and a board or wire antenna.

    In context, if you are talking of a raw IR transmitter (the logical
    other end of the IR receiver/decoder module) there is no ready made
    modules of those, I know of, as those, as said, are driven from the
    remote IC, in typical consumer remotes.

    I do know there are "enclosed" radio transmitter/receiver modules. one
    could use, but typical mass manufacturers build their own "on board".
     
  11. joseph2k

    joseph2k Guest

    Damn, you are hard headed. You made me google for you. Feed "IR
    transmitter IC" to google and get this, among other things on the first
    page, "SDA2208-2 Siemens IR Remote Control TX/RX Driver, TV IC". Then you
    toss that to google.
     
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