Radio circuit

Discussion in 'Electronics & Electrics' started by @rt, Mar 4, 2010.

  1. @rt

    @rt Member

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    Hi Guys,
    Would anyone share a schematic for a AM or FM radio they have actually made from
    easily obtainable parts?

    I have tried Jaycar Short Circuits FM radio kit,
    Dick Smith Funway 2 Pocket transistor radio x 3
    Dick Smith Electronics 30 in 1 Electronics Kit (has a radio).

    None of these worked at all, except the Jaycar FM radio made some squealing noise.
    I don't want to have to run a ground wire to a tap, and I have a 1 Watt amplifier ready
    to use with it.
    Cheers, Art.
     
  2. OP
    OP
    @rt

    @rt Member

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    Also a question... Here is the Jaycar FM radio kit:
    http://www.jaycar.com.au/productView.asp?ID=kj8238

    I built it on a prototype board because I didn't want the amplifier chip in the circuit, and a radio is to be only part of a bigger project.
    Would it be an issue that one of the 2 coils are mounted about 5cm from the chip (instead of about 1cm on the supplied PCB)?
     
  3. OP
    OP
    @rt

    @rt Member

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    Jaycar FM Radio kit:
    [​IMG]

    DSE 30in1 Kit AM Radio:
    [​IMG]

    The coil L1 on the FM radio is formed on the PCB. It's not actually a coil,
    but a snake like pattern. The dimensions match very closely what was printed
    on the supplied PCB.

    I think the AM radio kit works, but is just unsuitable, and I can't hear any stations in a city area.
    It clicks if I short a 1.5 volt cell near it.
    I would be pissed if I'd paid $29.95 this for my kids (don't actually have any though).
    And don't get me wrong, I had a working crystal radio when I was about ten, and loved my 200-in-1 kit.
     
    Last edited: Mar 4, 2010
  4. Technics

    Technics Member

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  5. OP
    OP
    @rt

    @rt Member

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    The DSE Funway kit is based on that chip (or it's equivalent).
    I have about 10 of them, and have tried this circuit the most times. (about five of them).

    I was asking for someone who built one because I'm wondering if I should hear static.
    I can't hear anything.
    The circuit isn't incredibly complicated either.
     
  6. Technics

    Technics Member

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    I would expect to hear static. What is the output of the chip connected to? It needs an amp to drive anything but a crystal earpiece.
     
  7. OP
    OP
    @rt

    @rt Member

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    Yes, I have a few of the earphones you usually get with a crystal radio kit (those beige coloured ones).

    The dick smith kit does suggest a magnetic earphone though.
    The circuit always has one external transistor wherever you find it.


    Maybe I can make a PCB for the FM radio. I've got a PCB kit that's been waiting for a good reason to use.
    I would have to draw the tracks by hand though.
     
  8. OP
    OP
    @rt

    @rt Member

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    I got the DSE AM radio kit working :)
    I'd still like to make an FM radio PCB.
     
  9. 2xCPU

    2xCPU Member

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    Absolutely - yes.
    The two fly-leads from pins 13, 14 (with the extra twists) will detune the coil.

    The tuning cap (and associated components) also need to be closer to the TDA.

    That style of construction is ok for DC, but at RF, you need to much more careful.

    Also, your soldering iron looks like it is not hot enough.

    2.
     
  10. Foliage

    Foliage Member

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    I was going to say the same thing, when designing anything that uses high frequencies opposed to pure digital you need to make the tracks as short and as close to their sources as possible to avoid acting as an antennae, not to mention the extra capacitance and inductance you can introduce in the circuit.

    Having actual twisted wires lying everywhere will make it even worse. I would definitely recommend designing a PCB for the project. It does not cost that much to get a one off board printed.
     
    Last edited: Mar 5, 2010
  11. OP
    OP
    @rt

    @rt Member

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    Ok, I'll give it another shot on prototype board, and then try making a PCB if I have
    no luck there.
    The only issue is I have to draw the PCB by hand.
    It would be pretty hard to get the footprint right for the IC,
    Maybe I can use an 18 pin socket a guide while I'm drawing.
    Never done a PCB before, but I do have a starter kit that's been sitting here.
     
  12. LostBenji

    LostBenji Member

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    The FM radio receiver in the first pic is rather crude.
    The second of an AM radio is basic but functional. Wouldn't stress over wire lengths, the kits were designed for thos wires/components.

    http://www.somerset.net/arm/fm_only_one_transistor_radio.html
    for basic Rx.

    http://www.elecfree.com/electronic/wp-content/uploads/2008/02/simple-fm-receiver-by-tda7000.gif
    http://www.elecfree.com/electronic/simple-fm-receiver-by-tda7000/
    or better still, this for the above mentioned TDA7000 to expand on what Technics has already linked to. You can see that you are missing a few bits from a simple kit.
     
  13. 2xCPU

    2xCPU Member

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  14. dohzer

    dohzer Member

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    Maybe he can make a decent stereo with a DAB+ receiver, because all the ones I've seen in the stores are expensive crap.
     
  15. Foliage

    Foliage Member

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    There's loads of programs for drawing PCBs out there that come with all the footprints you already need. Not to mention it's much easier to just send a file off to the manufacturer then it is to send a drawing, I can't imagine many would accept that anyway. EAGLE is a good free one, Altium is great if you can get hold of a trial or a copy from uni etc, I'd grab a copy of eagle to play though, it can be quite fun. :)
     
  16. OP
    OP
    @rt

    @rt Member

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    Well since this is just for a clock project with a radio alarm option,
    it isn't a big deal that the radio isn't digital.
    I don't know if there's any kits out there, or how complicated it is to make one.

    Thanks to all who answered.
     
  17. 2xCPU

    2xCPU Member

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    I wouldn't get too excited about digital radio. Here in the UK, where DAB has been available for quite a while, many digital stations (including the BBC) are shutting down due to lack of interest.

    Given DAB is more suited to the UK scene than it is to Aus, I can't see being a big success.

    2.
     
  18. OP
    OP
    @rt

    @rt Member

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    [​IMG]

    This is FM Radio take 2, only still not working.
    This time I used the PCB inductor from the supplied PCB.
    This one might have an error I haven't found yet.
    The first one at least gave me the feeling it was a radio by making noises
    as I tuned through the band.
    This one just make the same static noise all the time.

    I'm tempted to buy a cheap pocket radio, disassemble it, and assembling it on a PCB again.

    That is because I have the amplifier on a separate PCB.
     
    Last edited: Mar 7, 2010
  19. OP
    OP
    @rt

    @rt Member

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    Yay! It works :)

    I just found two errors on the board because I'd stayed up late building it again.
    The far end of the tuning capacitor was connected to nothing in the above pic (you can't see that though).
    Art.
     
  20. LostBenji

    LostBenji Member

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    Up a tower somewhere....
    I wasn't refering to the amp section.


    At least you have a worker now. LoL, whats next he says......
     

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