Microcontroller based FM transmitter

Discussion in 'Wireless & RF Design' started by Xkyve, Sep 10, 2014.

  1. Xkyve

    Thread Starter Member

    Nov 30, 2012
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    I'm trying to build a microcontroller based FM transmitter which can change frequencies on the fly (88 - 108 Mhz) and is able to transmit 20-30 meters to cover my house. I know I can do this with analog c0mponents only, but I want to build it using a micro for educational purposes.

    Basically the microcontroller will sample an audio signal or will receive that audio signal through Bluetooth and will output a signal to the RF frontend for FM transmission.

    I have basic knowledge of electronics but I'm new to the RF domain. Could you guide me to build the RF frontend? I imagine I need a configurable oscillator that is able to communicate with the microcontroller to set the carrier frequency and modulate a signal received from the microcontroller (through DAC?) Can you recommend me any components or do you have links to similar projects?

    P.S.: I've seen this can be done with a Rasberry Pi, but I wish to use a simpler microcontroller, perhaps an NXP LPC13xx or LPC17xx.

    Thank you
     
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
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    the dac output will not be stable enough to set the frequency, use a pll programmed by the micro.
     
  3. bertus

    Administrator

    Apr 5, 2008
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  4. Xkyve

    Thread Starter Member

    Nov 30, 2012
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    Ok, so a programmable PLL or oscillator should do the trick (any more links are welcome). What about the output stage? Could I wire the antenna directly to the output pin of the oscillator which gives the clock? What methods are there to amplify the signal at the output of the oscillator? What would be the ideal antenna length?

    Later edit:
    I found this device:
    http://www.farnell.com/datasheets/273003.pdf
    It says it can be programmed, but I can't figure out how.
     
    Last edited: Sep 10, 2014
  5. Newtonfigley

    New Member

    Sep 11, 2014
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  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    It looks like the CSX series are one time programmable.
    The frequency should be given at the order.

    The silabs chip can give the frequency given by I2C commands.

    Bertus
     
  7. Xkyve

    Thread Starter Member

    Nov 30, 2012
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    Can you give me some alternatives to Si570? I'm having trouble finding a supplier for Europe. My main suppliers are farnell.com and tme.eu
     
  8. bertus

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  9. MrChips

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  10. Xkyve

    Thread Starter Member

    Nov 30, 2012
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    2
    That chip does not allow on-the-fly modification of the transmitting frequency. It uses external components to set the frequency.
     
  11. bertus

    Administrator

    Apr 5, 2008
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    Xkyve likes this.
  12. johnyradio

    Member

    Oct 26, 2012
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    Xkyve likes this.
  13. Xkyve

    Thread Starter Member

    Nov 30, 2012
    32
    2
    Thanks for the link.
    Wow, that component is really expensive :)
    Maybe I will try a microcontroller with a high speed clock generator to try and build something like the PiFm for the Raspberry Pi.

    Later edit:
    I'll leave here a message just in case anyone has the same goal as me.
    I found some Si4713 chips at farnell and I will use those.
     
    Last edited: Oct 11, 2014
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