Simple Radio TX/RX Project - Transmit an on signal for LED

Discussion in 'The Projects Forum' started by Imdsm, Aug 22, 2011.

  1. Imdsm

    Thread Starter Member

    Feb 11, 2011
    39
    0
    Hi there,

    I am going to be building with my brother a remote control car in the next 12 months, quite a big one, he will be doing the engineering and I'll be doing the electronics. For that, I need to swot up on radio. I could just buy a chipset like the TX2/RX2 but I like to learn things properly.

    So, basically, what I want to do for a first project, is have two breadboards, one a receiver and one a transmitter. On the transmitter I want to press a button and it transmit an on signal, on the receiver I want to be able to detect that and light up and LED. I think this would be a good starter radio quest.

    Any ideas on how I would do this, I've read quite a few tutorials today, I'm not looking for a full diagram just some pointers, friendly advice and encouraging tips!

    Cheers
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Well, building your own transmitter without guidance could get you into hot water very quickly with the authorities. If you transmit on an unauthorized frequency, or "splatter" on to adjacent frequencies that you might be authorized to transmit on, the authorities will have no sense of humor about it.

    In the States, if you get caught transmitting above various power levels on various frequencies without a license to do so, your equipment will be confiscated, you will be put in jail, and heavy fines will be assessed, usually in the neighborhood of $10,000 per occurrance.

    You would be much better off to purchase a commercially made transmitter that is on a frequency approved for use where you live.
     
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  3. BurninBri

    New Member

    Aug 16, 2011
    27
    3
    As Sgt Wookie stated, you do want to make sure you're in the correct frequency range and keep your output power under the maximum specifications for the frequency band you choose. Initially, I would have said look at a product like this in the 433MHz band.
    http://www.parallax.com/tabid/768/ProductID/112/Default.aspx
    As you can see, it uses a chip from Link. And I had originally thought that the 433MHz band was available in Europe as well as the U.S.

    However, after a quick search for the Wiki:
    http://en.wikipedia.org/wiki/Low-power_communication_device

    However - I see that you are in the U.K. I just did a quick search on the ISM band, and this was one of the first few links (it's a .doc, sorry about that) - that basically says 433MHz is not allowed in the U.K. since it's for radio amateurs.

    So you really need a "pre-approved chipset with integral antenna" if you're playing in that band. But hopefully from the doc, you saw some other bands that may be much less restrictive.

    I think you should also ask yourself what the system needs to do. This will depend on what type of modulation scheme you use:
    Questions to ask:
    do you need low transmit power?
    low receive power?
    high bandwidth?
    What range do you need (how far) for the communication?
    Line of sight? Or with obstacles (and what kind)?
    How robust does the communication need to be?
    Two-way communication to ensure message delivery?

    These questions can help you choose a frequency band as well as a modulation scheme (FSK/ASK/etc.)

    Once you get those questions resolved, you can start building a basband modulator and then use a mixer to move it to the proper frequency. However, it may be easier (and more power efficient) just to use a chip that has already been made for this.

    Hope these few pointers help.
     
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  4. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    Yes, go with a chip. There are several options, I like most THIS which may also be appropriate for your application. If you never worked with RF it will take a long time for you to build a circuit with discrete components that is stable and built according to legal requirements.
     
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  5. BurninBri

    New Member

    Aug 16, 2011
    27
    3
    Yes, I meant to say "Linx" not "Link" for the chip-vendor mentioned above. They're a good company. Also note there is some additional information which you may want to use based on RC cars and boats:

    http://hoylakemodelboatclub.com/OFCOMINFORMATION.aspx

    Good luck!
     
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  6. Imdsm

    Thread Starter Member

    Feb 11, 2011
    39
    0
    Thanks for the replies guys!

    The reason I wouldn't be looking to use a chip is because in my quest for learning electronics better, I want to understand how radios work. My main goal in the next 12 months will be to use this for a remote controlled surface model car, but this isn't the primary use. I also want to learn to make radios for the enjoyment of me making it. Buying a chipset for me is a little like buying an R/C car ready made. Sure, it's a lot easier, and yes, I won't have judge dread kicking down my apartment door - but I won't have any pride in it and more importantly, I won't have achieved anything by doing it.

    I understand there are legalities with broadcasting, but I would be looking to operate in one of the general use legal bands, and to begin with, the breadboards will both be on my work bench so they won't need to travel far.

    What I really want to do to begin with is be able to send on/off signals to a receiver, once I have both circuits working, I can just integrate them into a transceiver for two way traffic.

    If, for example, I got some 27 MHz chips (commonly found in R/C models such as the one I've dissected at home), wouldn't this make it legal if I keep the power output low?

    @BurninBri

    do you need low transmit power?
    - for now, yes, it only needs to travel a few feet, but power is not an issue really

    low receive power?
    - no issue really, it'll have a power source

    high bandwidth?
    - depends on what you'd call high? for now, i don't know :)

    What range do you need (how far) for the communication?
    - for now, a few feet, if that

    Line of sight? Or with obstacles (and what kind)?
    - no real obstacles for now, not for this project

    How robust does the communication need to be?
    - well the receivers needs to be able to determine whether HIGH or LOW is being transmitted, without a lot of latency

    Two-way communication to ensure message delivery?
    - not right now

    But like I said, not really looking for a chip, looking to learn and build myself, so any pointers to manual construction would be greatly appreciated!
     
  7. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
    193
    Hi Imdsm,

    What you are looking to do is no small feat. We understand the joy of making your own circuits, MP3 players, microcontroller-controlled RC cars, etc., it's just you're talking about radio frequency, RF, which is, for lack of a better description, a black art. It requires lots time (years), experimenting, and some very expensive equipment including spectrum analyzers to do right. Not trying to deter you in the least, it's just immensely easier to use something ready-made and focus your attention on the programming, bells and whistles, etc. of your project. Making your own transmitter and receiver is like learning to build a computer at the circuit level so you can program an IC for your project.

    Anywho, let's assume you want to charge forward regardless. Check out:

    http://www.arrl.org/

    These are the hobby RF masters. And as a great wealth of knowledge on RF and electronics in general, check out their latest book:

    http://www.amazon.com/ARRL-Handbook...095X/ref=sr_1_2?ie=UTF8&qid=1314109465&sr=8-2

    I wish you the best of luck although I do not envy your quest. :)
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    1,728
    I was about to post the link to ARRL when I saw that elec_mech had already posted it.
    The ARRL is a great organization, and the handbook is pure gold. However, as implied/cautioned previously, the RF spectrum will be chopped up very differently in the UK than it is in the ARRL handbook; as the book is oriented towards the US RF spectrum.

    I have no idea if there is a similar organization in the UK. However, you might find out through the ARRL, or perhaps a kind amateur radio person will provide some info on that.

    In the States, you can build receivers for just about any frequency band with no problems. It's the transmitters that will get you in trouble. Your mileage (regulations) may (will) vary considerably.
     
  9. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    I have another thought to rain on you parade: say you hand build the worlds best legal low power transmitter and receiver and not only do your LED but you have the capability of controlling everything you wish on your car.

    How ya gonna steer this car? Give it gas? What knobs dials switches are you going to use? There are several nice things about buying a ready made controller besides it working right out of the box or you take it back: it is going to have a common, well thought out, and fairly rugged set of controls on it.
     
  10. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    The english counterweight of the ARRL is the RSGB (as the OP is UK based):
    http://www.rsgb.org/

    More RF related links can be found in this thread that I made:
    RF related links

    Bertus
     
  11. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
  12. upand_at_them

    Active Member

    May 15, 2010
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