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FM transmitter (mod4)

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by bananasiong, Oct 26, 2006.

  1. bananasiong

    bananasiong New Member

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    Do you mean I can't tune to it with a cheap radio if I reduce the supply voltage?
     
  2. audioguru

    audioguru Well-Known Member Most Helpful Member

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    A cheap FM radio gets overloaded when it is near a transmitter. When it is overloaded then it might not work. With a 5V supply, the transmitter's power is much less so a cheap radio might not be overloaded.
     
  3. Hero999

    Hero999 Banned

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    That depends on whether the mains adaptor's output current and whether it's regulated or not. If it's rated for a fairly high current and isn't regulated then you'll get about 8V with the transmitter connected. This is pretty similar to a 9V battery but you'll get loads of mains hum on the output because of the ripple (the filter capacitors are normally undersized).

    Run it from a 9V mains adaptor using a 5V regulator for the oscillator section with a huge 100:mu:f capacitor across the power supply rails.
     
  4. dave

    Dave New Member

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  5. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I designed the mic preamp for a 5V regulated supply. It won't work if the voltage is different.
     
  6. bananasiong

    bananasiong New Member

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    Okay, thanks. I'll try with 9 volts first.
     
  7. Hero999

    Hero999 Banned

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    Sorry, I meant run the oscillator and pre-amp stages from a 5V regulator.
     
  8. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I used a low-dropout regulator that still regulates very well with a 5.0V output when the battery voltage drops to 5.4V. An ordinary 7805 regulator doesn't regulate if its input voltage is less than about 7.5V.
     
  9. Hero999

    Hero999 Banned

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    I wasn't talking about a battery, I was talking about a powerbrick.
     
  10. bananasiong

    bananasiong New Member

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    Hi,
    I've almost completed putting the components together. It is around 10 x 3 cm.
    Here are my questions:
    I couldn't find a 160k (R2) resistor but I can get 150k. Can it be replaced?
    Can I replace the 30k (R3) with a 33k resistor?
    Or R2 and R3 need to be in ratio to provide the voltage devider?
    What's the value should C4 be? Operating at 88 to 108MHz.
    Can I replace the 30pF (C12) with a 22pF capacitor?
    The turns of my coils is not touching to the neighbour turn exactly, just very near. Can this affect the operation?
    I'm not using low drop-out voltage regulator but a 7805. I think it should be okay if I use a power supply with 9 volts? How if I use a 9 volts rechargeable battery? I don't think it last very long.
    Is there any suggestion on cutting the metal on the veroboard to disconnect the connection? Usually i use penknife to cut, very troublesome and I don't like to do this.

    Thanks
     

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  11. audioguru

    audioguru Well-Known Member Most Helpful Member

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    It looks nice but is twice as long as mine.

    160k and 30k are standard 5% values. The ratio must be close, use 180k for R2 and 33k for R3.

    I don't know if FM radio stations in your country use pre-emphasis (treble boost) like in Europe or like in North America. Ask the engineer at a local FM station.

    Yes.

    My coils have enamel insulation and are made with the turns touching. If yours isn't insulated then the turns must not short together, but a space will change the inductance. Maybe it can still be tuned to an FM band frequency.

    A 7805 regulator is fine if you use a 9V power supply. A Ni-Cad or Ni-MH rechargable "9V" battery is actually only 7.2V so cannot power some 7805 regulators. Its charge will power the transmitter with a low dropout regulator for about 1/2 hour to 1 hour. A 9V alkaline battery will power the transmitter with a low dropout regulator for about 6 hours.

    I use a drill-press and sometimes just a drill bit held in my hand. A real Veroboard cutting tool is like a drill bit in a handle.
     
  12. Hero999

    Hero999 Banned

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    If you don't have a drill bit of the correct size or a special stripboard tool then don't worry. The best way is to gently make two cuts next to each other then remove the bit inbetween with a soldering iron. Sometimes it's best to solder a piece of copper tinned wire to it, leave it to cool then pull it off, it should remove the track.

    If you want to save space and money then use the LM78L05 in a T092 package, but as audioguru says it's only a goods idea if you're planning to use a 9V power supply, in which case it's also a good idea to add a 100:mu:F capacitor across the power rails.
     
  13. bananasiong

    bananasiong New Member

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    twice!! I've tried my best.. :)

    Thanks

    Yes, I'm using enamel coated wire as well. But the turns are not touching, maybe caused by experience??

    Do you use drill bit for components or bigger drill bit?

    Thanks :D
     
  14. audioguru

    audioguru Well-Known Member Most Helpful Member

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    My drill bit has a diameter a little more than the width of a copper track on the Veroboard. Here is a pic showing track cuts and a red screw-hole:
     

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  15. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Buy a proper track cutting tool, they cost very little, and it's SO much easier than using a drill bit - I used a drill bit for years, then I got round to buying the proper tool, I couldn't believe the difference!.
     
  16. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I don't know where to buy real Veroboard anymore. I think Vero doesn't make it and the employees set up their own company but its website doesn't say much.
     
  17. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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  18. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Maplin's spot face cutter looks like the last real Veroboard one I had, same type and colour. My first one had a wood handle, not plastic.
    I don't have the tools anymore and there aren't any Maplin shops anywhere around here. My drill-press can cut two spots per second.
     
  19. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    I whip my spot face cutter out of my pocket and cut tracks anywhere!, a drill-press seems a little less convenient?.

    Maplin was only an example, almost any electronics shop stocks them - certainly RS Components do, and they are worldwide.
     
  20. Dr.EM

    Dr.EM New Member

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    I agree. I used to use a drill bit, but before a project that I knew would need many breaks, I bought the proper handled tool. It is very much better yeah. Mine was from Rapid :)
     
  21. bananasiong

    bananasiong New Member

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    How if the track nearby is also pulled out accidentally? :D
    This package cost much right?
    There are already one before and one after the voltage regulator, do I still need it?
    Usually we cut the tracks before or after putting in the components?

    Thanks
     

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