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Microcontroller Based RC Receiver Project

Discussion in 'General Electronics' started by Daniel Rubin, Aug 29, 2003.

  1. Daniel Rubin

    Daniel Rubin Guest

    Hello,

    I have been doing some digging to find some information needed to
    start a new project to build a RC (radio control) FM modulation
    receiver for use with 72 MHz aircraft frequencies based on one of the
    new PIC nanowatt chips. I have come up with very little on the
    subject. Has anyone run across any relevent articles in the web or in
    this list that may help me? An example of an existing product can be
    found at http://www.slowfly.com/DetailPages/rffs100.html. Any ideas?

    - Dan
     
  2. I can't see how a microcontroller can be used to build a receiver, altho
    of course it would make a fine intelliegent decoder and ESC.

    What you need is access to coils, crystals, ceramic filters and probably
    a good sweep generator and spectrum analyser.

    If its of any help to you, there are a few schematics of 35/40Mhz DIY
    receievers available if you follow all of the link here->
    http://www.norcim.fsnet.co.uk/#U and you could probably cahnge to &2Mhz
    by simply using a different Xtal and a change to the two front-end RF
    stage coils, and the trap coil. IF would be unchange.

    Kits of bits that might be adapted are avaialbe from
    http://www.micronradiocontrol.fsnet.co.uk/

    Good luck!
     
  3. Dave VanHorn

    Dave VanHorn Guest

    Have a look at zeevo, and Atmel's offerings.
     
  4. I am sure I would, If I had the faintest idea where to start.
     
  5. Yerrs, but those are not microcontrollers. They are specialised analogue
    IC's. And designed for short range high data rate transmission, not long
    range low rate, which is what we want.
     
  6. Daniel Rubin

    Daniel Rubin Guest

    It must be possible to use nothing but a PIC to detect and process the
    incoming signal. If you look at this close-up of the RFFS-100 in the
    link below you will see no coils. The crystal for the desired channel
    connects directly to the PIC.

    I have extensive experience programming the PIC and would love to play
    around and try to build something similiar from scratch. I am lacking
    on the RF side...

    http://users.joplin.com/~bselman/rffs100.htm

    Thanks
    - Dan
     

  7. YOU cannot use a PIC to amplify low level RF, period.


    That has many other components apart from the large IC, which may, ormay
    not, be a PIC. a PIC talks high level digital signals, and maybe low
    frequency high level analogue. You HAVE to have an anlogue circuit
    somewhere. Using a microcontroller to synthesize the local ocsilllator
    is possible, but you still need a front end and mixer of some sort, and
    doing without some form of filtering there is dangerous in the extreme.

    As far as that reciever goes, its a two IOC design with preset crustal
    solderd in. Its not possible to see what IC'ds are used, but one is
    probably an integrated RF/IF/detector/Mixer/oscillator chip, and the
    other is probably a pic doing decode - instead of teh standard CMOS 4017 IC.


    My guess is there are a few coils on the back, and probably a few
    ceramic resonators.
     
  8. Dave VanHorn

    Dave VanHorn Guest

    no, but mchip does make an rfpic line, which may be what we are seeing here.
    http://www.microchip.com/1000/pline/frequency/rfcats/rfpic/
    given that they talk about firmware for the pic on that page, immediately
    below the picture, it seems rather likely.


    a PIC talks high level digital signals, and maybe low
    there are other ways to receive rf, than the lo/mixer approach.
    the board is laying flat on the background.
     
  9. Daniel Rubin

    Daniel Rubin Guest

    More information... I found good photo of the back of the board:

    http://www.rcmicroflight.com/images/dec02/RFFS100_01.jpg

    It appears the 16-pin chip in the photo of the front of the board that
    is connected to the crystal is not a PIC. This must be one of those
    "integrated RF/IF/detector/Mixer/oscillator" chips you mention below.
    Does anyone have a part no. for something like this so I can find a
    datasheet? That 8-pin chip on the front is a LTC1516 5v charge pump
    DC/DC conv.

    The PIC is the 8-pin chip on the back of the board and controls the
    magnetic actuators. There are other chips on the back of the board,
    but no coils or apparent resonators.

    - Dan
     

  10. Indeed, and I have built a few. Mostly they don't work as well, and none
    use all digital technology.

    You are making sweeping statements about a subject you clearly know a
    little about. I am making sattements about a subject both studied and
    got a masters in and did as a profession for many many years.


    There ois no PIC in the world that I know of that can do anything useful
    with an NBFM modulated signla at 72Mhz, and 2uV level buried in an RF
    spectrim of sheer choos, without some sort of amplification, and some
    basic filtering to get the other stiff out as well as boost teh wanted
    stuff.

    Even DSP's which are far more applicable, need to see signals that are
    of a level they can digitise - which menas at least a 60dB boost, and
    that again will need some form of out of band filtering, and AGC,
    otherwise other strong signals will overload it.

    Of course, with a DSP, once more or less digitised, its only software to
    do a decent IF strip, detector and smart decoding. But you will still
    need something at the frin tend to do teh initial amplification and
    filtering.


    Oh well. Perhaps there is another board.

    However, if you know all about it, why don't you *** off and make a mint
    out of sellng them instead of asking someone else how to do it?
     

  11. Dunno what that is for tho?


    There have to be. For decent performance at least. At a pinch you can
    use ceramic resonators to do everythiung beynbd teh mixer, but teh front
    end? Well you COULD just stick an antenna straight into teh mixer, but
    it would have vile alternate channel and out of band rejection, and
    probably transmit illegal amounts of LO signals itself.

    However, if one is producing a kit to sell to the gullible, who cares?

    If you want a schematic of a decent DC receiver, look
    here...http://www.norcim.fsnet.co.uk/Index_files/image017.jpg

    Fr9om p[age http://www.norcim.fsnet.co.uk/#U

    As you will see, this uses 4 coils in all, and 2 Xtals and 2 ceramic
    resonators. Its not totally 'state of the art' but is a damned good
    small dual conversion superhet design, and works very well.

    It has been DEVELOPED to fix and address typical problems found in real
    life situations. Not just thrown together as a project by one guy who
    managed to get the prototype working once, in a screened room with a
    transmitter 5 feet away...:)
     
  12. Dave VanHorn

    Dave VanHorn Guest

    so figure it out mr genius.. who pissed in your cornflakes
    quite unnecessary, i never made any claims to greatness, just made some
    observations that obviously pissed you off somehow.
     
  13. Daniel Rubin

    Daniel Rubin Guest

    This thread started out as a request for info... why it turned into a
    flame fest I don't know?

    I wanted to build a RC receiever "in my spare time". I wanted it to
    be small and I knew it could be done because of the existing
    commercial product called the RFFS-100 (links to photos where posted).
    From the photos of the product I could see no visible coils or
    obvious RF circuitry. Hence the initial question. I have found a lot
    of good info on the subject. Thanks also for that receiver
    schematic...

    BTW...

    The RFFS-100 has a range of 1000 ft., it is FCC certified and is being
    used by 1000s of RC modelers right now. Hardly a "thrown together"
    project? All of that with no visible coils? Must be impossible... I
    might as well give up :)

    - Dan
     
  14. Dave VanHorn

    Dave VanHorn Guest

    i think np woke up grumpy this week.

    receiver design isn't simple, unless you're willing to compromise a lot.
    for example, you -could- do a receiver using a tuned cavity, and pulsed
    microwave transmitter on 10.525 or 24 ghz. pretty directional, pretty deaf,
    and pretty wide open to interference, but also pretty simple.

    engineering is the art of compromise.
     
  15. Johnboy

    Johnboy Guest

    Just out of curiosity, why would you want to build a receiver
    when you can buy one that works perfect, is built by a
    100 million dollar company, has 7 channels and only
    costs $75.00?
     
  16. Why would anyone want to design a model airplane, when you can just go
    out and buy an ARF? ;-)

    -tih
     

  17. My first receiver used 4 transistors, one RF coil, one RFC, and two
    audio transformers.

    The one I flew a lot that actually worked had one less audio transformer
    and one more transistor.

    27Mhz single channel stuff. would receibve just about anything within
    1/2 Mhz from 27 :) :)

    So I built a 5W transmitter. I could fly anybody elses model with that,
    and in fact used it to get someones futaba equipped model back when it
    ran out of range on their 90mW tranny :). Nobodies signal was stronger
    than mine.
     

  18. Because you can build a better one for $50?
     
  19. Dave VanHorn

    Dave VanHorn Guest

    i'm not advocating this, i'm just discussing it.
    but i wouldn't take on a project like this to save 25 bux.
    i would do it to learn.
     
  20. Johnboy

    Johnboy Guest

    OK guys, lets go! I have tons of circuits already, but would
    like to see something processor controlled. What do you have?
     
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