Arduino and NS73M FM transmitter, RTTL Tones

I got on of these Sparkfun NS73M FM transmitters for use with my Arduino. It is controlled over the SPI interface with three wires, and more importantly at 3.3v. Also, it has standard Left and Right inputs, so a MP3 player or, in my case, i used the Arduino Tone RTTL library to play some melodies. the hardest part of getting this thing to work is the SPI interface. Which is actually quite a bit easier since someone has aready done the hard work. All i had to do was hook it up according to the schematic i found(now attached) and change the frequency it transmits at.

To change the transmission frequency, you first want to go to the Vacant FM Frequency Finder and find a open channel in your area. Then, once you found one, a little bit of conversion is needed. I choose 96.7Mhz for my area.
So what you do is: (FMfreq + 0.304)/0.008192 where FMfreq is 96.7. That equals about 11792.
Then it needs to be converted to binary with Google: 11792 to binary which gets B10111000010000 
Next, it must be 16 digits long, so add some zeros in front until you get 16 digits. I added two 0s: B0010111000010000.
Take the last 8 digits and that is register 3(00010000), and the first 8 digits are register 4(00101110).
In my code it looks like this:

spi_send(0x03, B00010000); //Register 3: Set broadcast freq to 96.7, lower byte
spi_send(0x04, B00101110); //Register 4: Set broadcast freq to 96.7, upper byte

Pics:

Note how i soldered the pins: easier to use on breadboard with  labels facing up.

Scheme for Arduino

Code: The following sets the frequency and initializes the transmitter. this would be good for hooking a MP3 player to right and left inputs:

/*
    12-1-2007
    Cai Maver, caimaver(at)yahoo.com
    ARRRduino+NS73M v0.3

    This code allows an Arduino Diecimila to control an NS73M FM Transmitter Module (Arrr matey!)

    This sets the NS73M (available from Sparkfun, SKU#: WRL-08482) to transmit
    at 2mW with 75us pre-emphasis (the standard for North America) on 97.3 MHz.

    Use this formula to determine the register values for a new transmitting frequency (f):

    (f + 0.304)/0.008192 <-- use only the whole number and convert the result to
       16-bit binary where the lower byte goes in register 3
       and the upper byte goes in register 4

       ex.: for 97.3 MHz, (97.3 + 0.304)/0.008192 = 11914.55...
       11914 = B0010111010001010 so
                                            Reg 3=B10001010
                                            reg 4=B00101110

                                  ex 96.7
                                  //add "2" "0"s to the begginning... 16 long
                                  11792 = B0010111000010000
                                  reg 3 = B00010000 //second half goes here, 8 long
                                  reg 4 = B00101110 //first half goes here
    A future version of this code will allow for on-the-fly frequency changes

    Thanks to Nathan Seidle at Sparkfun and Jim "ZAPNSPARK" G. for sharing their NS73M code!
*/

int CK = 12;  //clock pin
int DA = 11;  //data pin
int LA = 10;  //latch pin

void setup(){
  Serial.begin(9600);  //begin Serial connection for debugging

  pinMode(CK, OUTPUT);
  pinMode(DA, OUTPUT);
  pinMode(LA, OUTPUT);
  digitalWrite(LA, LOW); //unlatch transmitter
  delay(100);  //Wait for VDD to settle


  spi_send(0x0E, B00000101); //Software reset

  spi_send(0x01, B10110100); //Register 1: forced subcarrier, pilot tone on

  spi_send(0x02, B00000011); //Register 2: Unlock detect off, 2mW Tx Power

  spi_send(0x03, B00010000); //Register 3: Set broadcast freq to 96.7, lower byte
  spi_send(0x04, B00101110); //Register 4: Set broadcast freq to 96.7, upper byte

  spi_send(0x08, B00011010); //Register 8: set Osc on band 2

  spi_send(0x00, B10100001); //Register 0: 200mV audio input, 75us pre-emphasis on, crystal off, power on

  spi_send(0x0E, B00000101); //Software reset

  spi_send(0x06, B00011110); //Register 6: charge pumps at 320uA and 80 uA

  Serial.print("Transmitting");  //for debugging


}
void loop()
{

}

void spi_send(byte reg, byte data)  //routine to send Register Address and Data as LSB-first SPI
{
    int x;
    int n;
    digitalWrite(LA, LOW);

    for(x = 0 ; x < 4 ; x++)      //send four-bit register address
    {
   digitalWrite(CK, LOW);    //Toggle the SPI clock
   n = (reg >> x) & 1;  //n is the xth bit of the register byte
   if (n == 1){
  digitalWrite(DA, HIGH);    //Put high bit on SPI data bus
   }
   else {
  digitalWrite(DA, LOW);     //Put low bit on SPI data bus
   }
   Serial.print(n);     //send bit to serial connection for debugging
   digitalWrite(CK, HIGH);   //Toggle the SPI clock
    }

    for(x = 0 ; x < 8 ; x++)      //send eight-bit register data
    {
   digitalWrite(CK, LOW);    //Toggle the SPI clock
   n = (data >> x) & 1;
   if (n == 1){
  digitalWrite(DA, HIGH);    //Put high bit on SPI data bus
   }
   else {
  digitalWrite(DA, LOW);    //Put low bit on SPI data bus
   }
   Serial.print(n);    //send bit to serial connection for debugging
   digitalWrite(CK, HIGH);  //Toggle the SPI clock
    }
    delayMicroseconds(1);   //might not be needed, supposedly unstable command anyway

    digitalWrite(LA, HIGH);      //Latch this transfer
    delayMicroseconds(4);
    digitalWrite(LA, LOW);

    digitalWrite(CK, LOW);  //This is to keep CK pin at 0V at end of data transfer
    Serial.print("\n");     // send new-line to serial for debugging
}

Code: The following sets the frequency, initializes the transmitter, AND it plays some popular melodies using the RTTL Tone library over FM 96.7:

/*
    12-1-2007
    Cai Maver, caimaver(at)yahoo.com
    ARRRduino+NS73M v0.3

    This code allows an Arduino Diecimila to control an NS73M FM Transmitter Module (Arrr matey!)

    This sets the NS73M (available from Sparkfun, SKU#: WRL-08482) to transmit
    at 2mW with 75us pre-emphasis (the standard for North America) on 97.3 MHz.

    Use this formula to determine the register values for a new transmitting frequency (f):

    (f + 0.304)/0.008192 <-- use only the whole number and convert the result to
       16-bit binary where the lower byte goes in register 3
       and the upper byte goes in register 4

       ex.: for 97.3 MHz, (97.3 + 0.304)/0.008192 = 11914.55...
       11914 = B0010111010001010 so
                                            Reg 3=B10001010
                                            reg 4=B00101110

                                  ex 96.7, (96.7 + 0.304)/0.008192 = 11792.4
                                  //convert to binary
                                  11792 = B0010111000010000//add "2" "0"s to the begginning... 16 long
                                  reg 3 = B00010000 //second half goes here, 8 long
                                  reg 4 = B00101110 //first half goes here

    Thanks to Nathan Seidle at Sparkfun and Jim "ZAPNSPARK" G. for sharing their NS73M code!
*/

int CK = 12;  //clock pin
int DA = 11;  //data pin
int LA = 10;  //latch pin

#include <Tone.h>

Tone tone1;


#define OCTAVE_OFFSET 0

int notes[] = { 0,
NOTE_C4, NOTE_CS4, NOTE_D4, NOTE_DS4, NOTE_E4, NOTE_F4, NOTE_FS4, NOTE_G4, NOTE_GS4, NOTE_A4, NOTE_AS4, NOTE_B4,
NOTE_C5, NOTE_CS5, NOTE_D5, NOTE_DS5, NOTE_E5, NOTE_F5, NOTE_FS5, NOTE_G5, NOTE_GS5, NOTE_A5, NOTE_AS5, NOTE_B5,
NOTE_C6, NOTE_CS6, NOTE_D6, NOTE_DS6, NOTE_E6, NOTE_F6, NOTE_FS6, NOTE_G6, NOTE_GS6, NOTE_A6, NOTE_AS6, NOTE_B6,
NOTE_C7, NOTE_CS7, NOTE_D7, NOTE_DS7, NOTE_E7, NOTE_F7, NOTE_FS7, NOTE_G7, NOTE_GS7, NOTE_A7, NOTE_AS7, NOTE_B7
};

//char *song = "The Simpsons:d=4,o=5,b=160:c.6,e6,f#6,8a6,g.6,e6,c6,8a,8f#,8f#,8f#,2g,8p,8p,8f#,8f#,8f#,8g,a#.,8c6,8c6,8c6,c6";
//char *song = "Indiana:d=4,o=5,b=250:e,8p,8f,8g,8p,1c6,8p.,d,8p,8e,1f,p.,g,8p,8a,8b,8p,1f6,p,a,8p,8b,2c6,2d6,2e6,e,8p,8f,8g,8p,1c6,p,d6,8p,8e6,1f.6,g,8p,8g,e.6,8p,d6,8p,8g,e.6,8p,d6,8p,8g,f.6,8p,e6,8p,8d6,2c6";
//char *song = "TakeOnMe:d=4,o=4,b=160:8f#5,8f#5,8f#5,8d5,8p,8b,8p,8e5,8p,8e5,8p,8e5,8g#5,8g#5,8a5,8b5,8a5,8a5,8a5,8e5,8p,8d5,8p,8f#5,8p,8f#5,8p,8f#5,8e5,8e5,8f#5,8e5,8f#5,8f#5,8f#5,8d5,8p,8b,8p,8e5,8p,8e5,8p,8e5,8g#5,8g#5,8a5,8b5,8a5,8a5,8a5,8e5,8p,8d5,8p,8f#5,8p,8f#5,8p,8f#5,8e5,8e5";
//char *song = "Entertainer:d=4,o=5,b=140:8d,8d#,8e,c6,8e,c6,8e,2c.6,8c6,8d6,8d#6,8e6,8c6,8d6,e6,8b,d6,2c6,p,8d,8d#,8e,c6,8e,c6,8e,2c.6,8p,8a,8g,8f#,8a,8c6,e6,8d6,8c6,8a,2d6";
//char *song = "Muppets:d=4,o=5,b=250:c6,c6,a,b,8a,b,g,p,c6,c6,a,8b,8a,8p,g.,p,e,e,g,f,8e,f,8c6,8c,8d,e,8e,8e,8p,8e,g,2p,c6,c6,a,b,8a,b,g,p,c6,c6,a,8b,a,g.,p,e,e,g,f,8e,f,8c6,8c,8d,e,8e,d,8d,c";
//char *song = "Xfiles:d=4,o=5,b=125:e,b,a,b,d6,2b.,1p,e,b,a,b,e6,2b.,1p,g6,f#6,e6,d6,e6,2b.,1p,g6,f#6,e6,d6,f#6,2b.,1p,e,b,a,b,d6,2b.,1p,e,b,a,b,e6,2b.,1p,e6,2b.";
//char *song = "Looney:d=4,o=5,b=140:32p,c6,8f6,8e6,8d6,8c6,a.,8c6,8f6,8e6,8d6,8d#6,e.6,8e6,8e6,8c6,8d6,8c6,8e6,8c6,8d6,8a,8c6,8g,8a#,8a,8f";
//char *song = "20thCenFox:d=16,o=5,b=140:b,8p,b,b,2b,p,c6,32p,b,32p,c6,32p,b,32p,c6,32p,b,8p,b,b,b,32p,b,32p,b,32p,b,32p,b,32p,b,32p,b,32p,g#,32p,a,32p,b,8p,b,b,2b,4p,8e,8g#,8b,1c#6,8f#,8a,8c#6,1e6,8a,8c#6,8e6,1e6,8b,8g#,8a,2b";
//char *song = "Bond:d=4,o=5,b=80:32p,16c#6,32d#6,32d#6,16d#6,8d#6,16c#6,16c#6,16c#6,16c#6,32e6,32e6,16e6,8e6,16d#6,16d#6,16d#6,16c#6,32d#6,32d#6,16d#6,8d#6,16c#6,16c#6,16c#6,16c#6,32e6,32e6,16e6,8e6,16d#6,16d6,16c#6,16c#7,c.7,16g#6,16f#6,g#.6";
//char *song = "MASH:d=8,o=5,b=140:4a,4g,f#,g,p,f#,p,g,p,f#,p,2e.,p,f#,e,4f#,e,f#,p,e,p,4d.,p,f#,4e,d,e,p,d,p,e,p,d,p,2c#.,p,d,c#,4d,c#,d,p,e,p,4f#,p,a,p,4b,a,b,p,a,p,b,p,2a.,4p,a,b,a,4b,a,b,p,2a.,a,4f#,a,b,p,d6,p,4e.6,d6,b,p,a,p,2b";
//char *song = "StarWars:d=4,o=5,b=45:32p,32f#,32f#,32f#,8b.,8f#.6,32e6,32d#6,32c#6,8b.6,16f#.6,32e6,32d#6,32c#6,8b.6,16f#.6,32e6,32d#6,32e6,8c#.6,32f#,32f#,32f#,8b.,8f#.6,32e6,32d#6,32c#6,8b.6,16f#.6,32e6,32d#6,32c#6,8b.6,16f#.6,32e6,32d#6,32e6,8c#6";
//char *song = "GoodBad:d=4,o=5,b=56:32p,32a#,32d#6,32a#,32d#6,8a#.,16f#.,16g#.,d#,32a#,32d#6,32a#,32d#6,8a#.,16f#.,16g#.,c#6,32a#,32d#6,32a#,32d#6,8a#.,16f#.,32f.,32d#.,c#,32a#,32d#6,32a#,32d#6,8a#.,16g#.,d#";
//char *song = "TopGun:d=4,o=4,b=31:32p,16c#,16g#,16g#,32f#,32f,32f#,32f,16d#,16d#,32c#,32d#,16f,32d#,32f,16f#,32f,32c#,16f,d#,16c#,16g#,16g#,32f#,32f,32f#,32f,16d#,16d#,32c#,32d#,16f,32d#,32f,16f#,32f,32c#,g#";
//char *song = "A-Team:d=8,o=5,b=125:4d#6,a#,2d#6,16p,g#,4a#,4d#.,p,16g,16a#,d#6,a#,f6,2d#6,16p,c#.6,16c6,16a#,g#.,2a#";
//char *song = "Flinstones:d=4,o=5,b=40:32p,16f6,16a#,16a#6,32g6,16f6,16a#.,16f6,32d#6,32d6,32d6,32d#6,32f6,16a#,16c6,d6,16f6,16a#.,16a#6,32g6,16f6,16a#.,32f6,32f6,32d#6,32d6,32d6,32d#6,32f6,16a#,16c6,a#,16a6,16d.6,16a#6,32a6,32a6,32g6,32f#6,32a6,8g6,16g6,16c.6,32a6,32a6,32g6,32g6,32f6,32e6,32g6,8f6,16f6,16a#.,16a#6,32g6,16f6,16a#.,16f6,32d#6,32d6,32d6,32d#6,32f6,16a#,16c.6,32d6,32d#6,32f6,16a#,16c.6,32d6,32d#6,32f6,16a#6,16c7,8a#.6";
char *song = "Jeopardy:d=4,o=6,b=125:c,f,c,f5,c,f,2c,c,f,c,f,a.,8g,8f,8e,8d,8c#,c,f,c,f5,c,f,2c,f.,8d,c,a#5,a5,g5,f5,p,d#,g#,d#,g#5,d#,g#,2d#,d#,g#,d#,g#,c.7,8a#,8g#,8g,8f,8e,d#,g#,d#,g#5,d#,g#,2d#,g#.,8f,d#,c#,c,p,a#5,p,g#.5,d#,g#";
//char *song = "Gadget:d=16,o=5,b=50:32d#,32f,32f#,32g#,a#,f#,a,f,g#,f#,32d#,32f,32f#,32g#,a#,d#6,4d6,32d#,32f,32f#,32g#,a#,f#,a,f,g#,f#,8d#";
//char *song = "Smurfs:d=32,o=5,b=200:4c#6,16p,4f#6,p,16c#6,p,8d#6,p,8b,p,4g#,16p,4c#6,p,16a#,p,8f#,p,8a#,p,4g#,4p,g#,p,a#,p,b,p,c6,p,4c#6,16p,4f#6,p,16c#6,p,8d#6,p,8b,p,4g#,16p,4c#6,p,16a#,p,8b,p,8f,p,4f#";
//char *song = "MahnaMahna:d=16,o=6,b=125:c#,c.,b5,8a#.5,8f.,4g#,a#,g.,4d#,8p,c#,c.,b5,8a#.5,8f.,g#.,8a#.,4g,8p,c#,c.,b5,8a#.5,8f.,4g#,f,g.,8d#.,f,g.,8d#.,f,8g,8d#.,f,8g,d#,8c,a#5,8d#.,8d#.,4d#,8d#.";
//char *song = "LeisureSuit:d=16,o=6,b=56:f.5,f#.5,g.5,g#5,32a#5,f5,g#.5,a#.5,32f5,g#5,32a#5,g#5,8c#.,a#5,32c#,a5,a#.5,c#.,32a5,a#5,32c#,d#,8e,c#.,f.,f.,f.,f.,f,32e,d#,8d,a#.5,e,32f,e,32f,c#,d#.,c#";
//char *song = "MissionImp:d=16,o=6,b=95:32d,32d#,32d,32d#,32d,32d#,32d,32d#,32d,32d,32d#,32e,32f,32f#,32g,g,8p,g,8p,a#,p,c7,p,g,8p,g,8p,f,p,f#,p,g,8p,g,8p,a#,p,c7,p,g,8p,g,8p,f,p,f#,p,a#,g,2d,32p,a#,g,2c#,32p,a#,g,2c,a#5,8c,2p,32p,a#5,g5,2f#,32p,a#5,g5,2f,32p,a#5,g5,2e,d#,8d";


void setup(){
  Serial.begin(9600);  //begin Serial connection for debugging
tone1.begin(8);
  pinMode(CK, OUTPUT);
  pinMode(DA, OUTPUT);
  pinMode(LA, OUTPUT);
  digitalWrite(LA, LOW); //unlatch transmitter
  delay(100);  //Wait for VDD to settle


  spi_send(0x0E, B00000101); //Software reset

  spi_send(0x01, B10110100); //Register 1: forced subcarrier, pilot tone on

  spi_send(0x02, B00000011); //Register 2: Unlock detect off, 2mW Tx Power

  spi_send(0x03, B00010000); //Register 3: Set broadcast freq to 96.7, lower byte
  spi_send(0x04, B00101110); //Register 4: Set broadcast freq to 96.7, upper byte

  spi_send(0x08, B00011010); //Register 8: set Osc on band 2

  spi_send(0x00, B10100001); //Register 0: 200mV audio input, 75us pre-emphasis on, crystal off, power on

  spi_send(0x0E, B00000101); //Software reset

  spi_send(0x06, B00011110); //Register 6: charge pumps at 320uA and 80 uA

  Serial.print("Transmitting");  //for debugging


}

#define isdigit(n) (n >= '0' && n <= '9')

void play_rtttl(char *p)
{
  // Absolutely no error checking in here

  byte default_dur = 4;
  byte default_oct = 6;
  int bpm = 63;
  int num;
  long wholenote;
  long duration;
  byte note;
  byte scale;

  // format: d=N,o=N,b=NNN:
  // find the start (skip name, etc)

  while(*p != ':') p++;    // ignore name
  p++;                     // skip ':'

  // get default duration
  if(*p == 'd')
  {
    p++; p++;              // skip "d="
    num = 0;
    while(isdigit(*p))
    {
      num = (num * 10) + (*p++ - '0');
    }
    if(num > 0) default_dur = num;
    p++;                   // skip comma
  }

  Serial.print("ddur: "); Serial.println(default_dur, 10);

  // get default octave
  if(*p == 'o')
  {
    p++; p++;              // skip "o="
    num = *p++ - '0';
    if(num >= 3 && num <=7) default_oct = num;
    p++;                   // skip comma
  }

  Serial.print("doct: "); Serial.println(default_oct, 10);

  // get BPM
  if(*p == 'b')
  {
    p++; p++;              // skip "b="
    num = 0;
    while(isdigit(*p))
    {
      num = (num * 10) + (*p++ - '0');
    }
    bpm = num;
    p++;                   // skip colon
  }

  Serial.print("bpm: "); Serial.println(bpm, 10);

  // BPM usually expresses the number of quarter notes per minute
  wholenote = (60 * 1000L / bpm) * 4;  // this is the time for whole note (in milliseconds)

  Serial.print("wn: "); Serial.println(wholenote, 10);


  // now begin note loop
  while(*p)
  {
    // first, get note duration, if available
    num = 0;
    while(isdigit(*p))
    {
      num = (num * 10) + (*p++ - '0');
    }
 
    if(num) duration = wholenote / num;
    else duration = wholenote / default_dur;  // we will need to check if we are a dotted note after

    // now get the note
    note = 0;

    switch(*p)
    {
      case 'c':
        note = 1;
        break;
      case 'd':
        note = 3;
        break;
      case 'e':
        note = 5;
        break;
      case 'f':
        note = 6;
        break;
      case 'g':
        note = 8;
        break;
      case 'a':
        note = 10;
        break;
      case 'b':
        note = 12;
        break;
      case 'p':
      default:
        note = 0;
    }
    p++;

    // now, get optional '#' sharp
    if(*p == '#')
    {
      note++;
      p++;
    }

    // now, get optional '.' dotted note
    if(*p == '.')
    {
      duration += duration/2;
      p++;
    }

    // now, get scale
    if(isdigit(*p))
    {
      scale = *p - '0';
      p++;
    }
    else
    {
      scale = default_oct;
    }

    scale += OCTAVE_OFFSET;

    if(*p == ',')
      p++;       // skip comma for next note (or we may be at the end)

    // now play the note

    if(note)
    {
      Serial.print("Playing: ");
      Serial.print(scale, 10); Serial.print(' ');
      Serial.print(note, 10); Serial.print(" (");
      Serial.print(notes[(scale - 4) * 12 + note], 10);
      Serial.print(") ");
      Serial.println(duration, 10);
      tone1.play(notes[(scale - 4) * 12 + note]);
      delay(duration);
      tone1.stop();
    }
    else
    {
      Serial.print("Pausing: ");
      Serial.println(duration, 10);
      delay(duration);
    }
  }
}

void loop(void)
{
  play_rtttl(song);
  Serial.println("Done.");
  delay(1000);
}

void spi_send(byte reg, byte data)  //routine to send Register Address and Data as LSB-first SPI
{
    int x;
    int n;
    digitalWrite(LA, LOW);

    for(x = 0 ; x < 4 ; x++)      //send four-bit register address
    {
   digitalWrite(CK, LOW);    //Toggle the SPI clock
   n = (reg >> x) & 1;  //n is the xth bit of the register byte
   if (n == 1){
  digitalWrite(DA, HIGH);    //Put high bit on SPI data bus
   }
   else {
  digitalWrite(DA, LOW);     //Put low bit on SPI data bus
   }
   Serial.print(n);     //send bit to serial connection for debugging
   digitalWrite(CK, HIGH);   //Toggle the SPI clock
    }

    for(x = 0 ; x < 8 ; x++)      //send eight-bit register data
    {
   digitalWrite(CK, LOW);    //Toggle the SPI clock
   n = (data >> x) & 1;
   if (n == 1){
  digitalWrite(DA, HIGH);    //Put high bit on SPI data bus
   }
   else {
  digitalWrite(DA, LOW);    //Put low bit on SPI data bus
   }
   Serial.print(n);    //send bit to serial connection for debugging
   digitalWrite(CK, HIGH);  //Toggle the SPI clock
    }
    delayMicroseconds(1);   //might not be needed, supposedly unstable command anyway

    digitalWrite(LA, HIGH);      //Latch this transfer
    delayMicroseconds(4);
    digitalWrite(LA, LOW);

    digitalWrite(CK, LOW);  //This is to keep CK pin at 0V at end of data transfer
    Serial.print("\n");     // send new-line to serial for debugging

}