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RX/TX modules

Discussion in 'Electronic Basics' started by Jason S, Sep 18, 2006.

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  1. Jason S

    Jason S Guest

    Hi,

    I would like to know more about RF Transmitters/Receivers to provide
    wireless communications from one low voltage device to another related low
    voltage device (ideally 6-12V). I've looking around on the internet but I'm
    still a little stuck.

    In the past, I've been cheating by purchasing those ready-made remote
    control switches and hard-wiring my existing circuits to the remote control
    (as in Keyfob transmitter!) and receiver. Has been working ok, but I want
    to do it properly now! No keyfobs!

    I have seen various **RX and TX "modules"** out in the market, but someone
    said you can't just connect them directly to a power source and antenna and
    expect them to work... I need a driver or something... not sure exactly what
    he called it... Decoder maybe?
    I've noticed a lot of the suppliers make it a little off-putting by not
    providing links for compatible drivers - especially for amateurs like
    myself. I mean, how do I know which driver to get for the RX/TX modules I
    decide to get?

    For argument's sake, let's just say I decide to purchase the "433MHz
    Wireless Modules" from Jaycar Electronics (ZW-3100 and ZW-3102). What
    driver circuits will work with these modules, and please explain to me why
    you chose them.

    Can anyone point me in the right direction?

    Thanks in advance,

    Jason.
     
  2. Most of these ready made RF modules are transparent serial in-out
    devices. If you feed a digital serial data stream in at one end, it
    comes out the other end, no need for any other "driver".
    Usually you'd have a microcontroller at either end and you communicate
    from micro to micro using the internal USART, so I guess you could call
    the micro the "driver". The micros don't know the difference between
    hard wiring together or running through these RF modules, they are just
    transmitting and receiving serial digital data.

    For example, lets say you had 5 digital inputs and you wanted to
    trasmit these digital signals to a reciever at the other end to control
    5 LEDs or whatever. You could use a PICAXE chip at the input end which
    scans the 5 inputs and sends a unique byte to the transmitter for each
    input saying if it's HIGH or LOW. Another PICAXE at the receiving end
    decodes this serial data sets the 5 outputs HIGH or LOW as required.

    Hope that helps.

    Dave :)
     
  3. Jason S

    Jason S Guest


    Thanks Dave for the info.
    I sorta get what you are trying to say. I looked up PICAXE on the net
    (www.picaxe.co.uk) briefly and can see these chips are programmable I/O
    chips... looks relatively easy, even for some of my other apps.

    Am I on the right track here? (block diagram) :
    Digital signals > Picaxe > TX Data Pin(Out) ~ ~ ~ Transmission ~ ~ ~ RX
    Data Pin(In) > Picaxe > Outputs.

    What if I only have 1 digital input that I want to transmit to the receiver
    at the other end? Would I still need a chip like the Picaxe on either end,
    or not?

    Regards,
    Jason.
     
  4. Yep, they are an easily programmable microcontroller.
    Perfect for a job such as this.
    Correct, that's all you do.
    Most likely you still need the PICAXE or some other microcontroller.
    Most RF modules are designed for a serial input, so need a minimum
    input "data rate" like 300baud. You can probably get modules that have
    digital level inputs though.

    Dave :)
     
  5. Jason S

    Jason S Guest


    Cool! I shall see how I go. It's great to know that these chips also come
    in different sizes (8/18/28/40pin)!

    Thanks again Dave.

    Regards,
    Jason.
     
  6. Silicon Chip have a regular PICAXE column and lots of good PICAXE
    projects, worth following.

    Once you've mastered PICAXE's you can step up to regular
    microcontrollers like PIC or Atmel AVR programmed in BASIC, C or even
    assembler.

    Also, as I mentioned in another thread, I think there is even a PICAXE
    uses group based in Sydney that meets every month.

    Have fun!

    Dave :)
     
  7. bigtom28

    bigtom28 Guest

    Much appreciated Dave. I'm gonna have fun with this! I've never used
    microcontrollers before, and these sound pretty simple enough. I shall have
    a look at that Silicon Chip column too.

    Regards,
    Jason.
     
  8. Jason S

    Jason S Guest


    Oh just one for question Dave. I've seen some example schematics of how
    those TX/RX are connected (typically), and they are connected to Encoder and
    Decoder IC's. Would I need to sandwich these in between the PICAXE and the
    Module, or no need?
    PICAXE>Encoder>TXmodule ~~~Transmission~~~ RXmodule>Decoder>PICAXE ???
    I'm sorta guessing that it would depend on how reliable I want the
    transmission, i.e. noise/interference elimination? Would I be correct to
    assume this?

    Jason.
     
  9. Lionel

    Lionel Guest

    No need. One of the big reasons to use a little micro like the Picaxe
    in this kind of device is that you can program it to do all that for
    you.

    No. Most serial<->parallel chips don't do error checking, & it's much
    easier to add code for parity (or checksumming, ECC, etc) checking
    into your program than it is to do it in hardware anyway.

    And best of luck with learning the PICAXE, or whatever chip you end up
    going with. Once you get over the initial learning hump, designing
    with embedded controllers is a lot of fun, so don't get discouraged if
    you find it a struggle at first. ;)
     
  10. No need if the RF module accepts direct serial input, it already has
    the "encoder/decoder" inbuilt, or simply doesn't need one. There are RF
    modules that will not accept a direct digital input and they are more
    difficult to use. The Jaycar ones will accept digital digital input
    judging from it having a specification for a certain data rate, but
    check the data sheet to be sure.
    If you want error correction/detection then you'll have to do this in
    the PIC. More advanced units like wirless RS232 modules will have their
    own inbuilt error checking. Open one up though and you'll find a
    microcontroller stuck on the front end of a standard RF module!
    Basic error detection would use simple parity checking, or you could
    simply send the same byte say 3 times in row. If the receiver micro
    does not get 3 bytes the same then it simply discards the data.

    Dave :)
     
  11. jasen

    jasen Guest

    I'd go with small microcontrollers and connect the devices to the serial
    port. i don't know of anyone that sells loose code emitters or detectors.

    how would I choose:

    look at the voltages it needs on the input and produces on the output
    choose something that can produce and something that can recognise a coded signal
    and connect them to the input of the transmitter or the output of the
    receiver respectively.

    Bye.
    Jasen
     
  12. jasen

    jasen Guest

    If you want the receiver end recognise your transmitter then yes you will,
    the receiver module will produce an output signal whenever it sees anything
    transmitting on 455Mhz, so you need to make the signal from your transmitter
    distinctive and make the receiver end discriminate between that signal and
    someone elses keyfob.


    Bye.
    Jasen
     
  13. Jason S

    Jason S Guest

    Thanks again!
     
  14. Jason S

    Jason S Guest

    Thanks Lionel!
     
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