Raduino as NBFM TX

Here is a neat, 30 minute hack for your Raduino to turn the Si5351 into a pretty stable, solid NBFM transmitter. The hack is to add a varactor diode in series with the reference crystal oscillator and drive it with audio. I used a very simple audio amplifier to boost up the audio. Here is the circuit:

Attach a small piece of wire to clock 2 to radiate the signal. Here is the sketch :

/**
 * This source file is under General Public License version 3.
 */
#include <Wire.h>
#include <si5351.h>
Si5351 si5351;

void setup()
{
  int32_t cal=0;
  
  si5351.init(SI5351_CRYSTAL_LOAD_8PF,25000000l, cal);
  si5351.set_correction(cal);  
  si5351.set_pll(SI5351_PLL_FIXED, SI5351_PLLA);
  si5351.set_pll(SI5351_PLL_FIXED, SI5351_PLLB);

  //si5351.drive_strength(SI5351_CLK2, SI5351_DRIVE_2MA);
  si5351.output_enable(SI5351_CLK0, 0);
  si5351.output_enable(SI5351_CLK1, 0);
  si5351.output_enable(SI5351_CLK2, 1);

  si5351.set_freq(14500000000l,  SI5351_CLK2);   
  
  delay(10);
}

void loop(){

}