Thursday, October 1, 2015

Arduino Zero DAC Overview and Waveform Generator Example

In this video we take a look at the digital to analog converter (DAC) on the Arduino Zero. We will look at a simple example how to use the DAC and then we will look at a more complex example that turns the DAC into a pseudo waveform generator. You can find the code from this video below.


//***************ZeroDACExample Sketch*******************************
//This sketch provides an example on using the DAC on the Arduino Zero.
//It was used in a video tutorial on the ForceTronics YouTube Channel.
//This code is free and open for anybody to use and modify at their own risk

void setup()
{
  Serial.begin(57600); //start serial communication
  analogWriteResolution(10); //set the Arduino DAC for 10 bits of resolution (max)
  analogReadResolution(12); //set the ADC resolution to 12 bits, default is 10
  
  //Get user entered voltage, convert to DAC value, output DAC value
  analogWrite(A0,setDAC(getVoltValue()));
}

void loop()
{
  delay(2000);
  Serial.println();
  Serial.print("Measured voltage value is ");
  Serial.println(convertToVolt(analogRead(A1))); //Read value at ADC pin A1 and print it

}

//this function converts a user entered voltage value into a 10 bit DAC value 
int setDAC(float volt) {
//formula for calculating DAC output voltage Vdac = (dVal / 1023)*3.3V
return (int)((volt*1023)/3.3);
}

//this function gets the user entered DAC voltage value from serial monitor
float getVoltValue() {
float v = 0; //variable to store voltage 
Serial.println("Enter the voltage you want the DAC to output (range 0V to 3.3V)");
v = readParameter();
if (v < 0 || v > 3.3) v = 0; //check to make sure it is between 0 and 3.3V
Serial.print("DAC voltage set to ");
Serial.println(v);
Serial.println("Outputting DAC value........");
return v;
}

//waits for serial data and reads it in. This function reads in the parameters
// that are entered into the serial terminal
float readParameter() {
while(!Serial.available()); //Wait for user to enter setting
return Serial.parseFloat(); //get int that was entered on Serial monitor
}

//This function takes and ADC integer value (0 to 4095) and turns it into a voltage level. The input is the measured 12 bit ADC value.
float convertToVolt(int aVAL) {
return (((float)aVAL/4095)*3.3); //formula to convert ADC value to voltage reading
}

//***************ZeroWaveGen Sketch**************************************
//This sketch generates a sine wave on the Arduino Zero DAC based on user entered sample count and sample rate
//It was used in a tutorial video on the ForceTronics YouTube Channel. This code can be used and modified freely
//at the users own risk
volatile int sIndex; //Tracks sinewave points in array
int sampleCount = 100; // Number of samples to read in block
int *wavSamples; //array to store sinewave points
uint32_t sampleRate = 1000; //sample rate of the sine wave

void setup() {
  analogWriteResolution(10); //set the Arduino DAC for 10 bits of resolution (max)
  getSinParameters(); //get sinewave parameters from user on serial monitor
  
  /*Allocate the buffer where the samples are stored*/
  wavSamples = (int *) malloc(sampleCount * sizeof(int));
  genSin(sampleCount); //function generates sine wave
}

void loop() {
  sIndex = 0;   //Set to zero to start from beginning of waveform
  tcConfigure(sampleRate); //setup the timer counter based off of the user entered sample rate
  //loop until all the sine wave points have been played
  while (sIndex<sampleCount)
  { 
//start timer, once timer is done interrupt will occur and DAC value will be updated
    tcStartCounter(); 
  }
  //disable and reset timer counter
  tcDisable();
  tcReset();
}

//This function generates a sine wave and stores it in the wavSamples array
//The input argument is the number of points the sine wave is made up of
void genSin(int sCount) {
const float pi2 = 6.28; //2 x pi
float in; 

for(int i=0; i<sCount;i++) { //loop to build sine wave based on sample count
in = pi2*(1/(float)sCount)*(float)i; //calculate value in radians for sin()
wavSamples[i] = ((int)(sin(in)*511.5 + 511.5)); //Calculate sine wave value and offset based on DAC resolution 511.5 = 1023/2
}
}

//This function handles getting and setting the sine wave parameters from 
//the serial monitor. It is important to use the Serial.end() function
//to ensure it doesn't mess up the Timer counter interrupts later
void getSinParameters() {
Serial.begin(57600);
Serial.println("Enter number of points in sine wave (range 10 to 1000)");
sampleCount = readParameter();
if (sampleCount < 10 || sampleCount > 1000) sampleCount = 100;
Serial.print("Sample count set to ");
Serial.println(sampleCount);
Serial.println("Enter sample rate or samples per second for DAC (range 1 to 100k)");
sampleRate = readParameter();
if (sampleRate < 1 || sampleRate > 100000) sampleRate = 10000;
Serial.print("Sample rate set to ");
Serial.println(sampleRate);
Serial.println("Generating sine wave........");
Serial.end();
}

//waits for serial data and reads it in. This function reads in the parameters
// that are entered into the serial terminal
int readParameter() {
while(!Serial.available());
return Serial.parseInt(); //get int that was entered on Serial monitor
}

// Configures the TC to generate output events at the sample frequency.
//Configures the TC in Frequency Generation mode, with an event output once
//each time the audio sample frequency period expires.
 void tcConfigure(int sampleRate)
{
// Enable GCLK for TCC2 and TC5 (timer counter input clock)
GCLK->CLKCTRL.reg = (uint16_t) (GCLK_CLKCTRL_CLKEN | GCLK_CLKCTRL_GEN_GCLK0 | GCLK_CLKCTRL_ID(GCM_TC4_TC5)) ;
while (GCLK->STATUS.bit.SYNCBUSY);

tcReset(); //reset TC5

// Set Timer counter Mode to 16 bits
TC5->COUNT16.CTRLA.reg |= TC_CTRLA_MODE_COUNT16;
// Set TC5 mode as match frequency
TC5->COUNT16.CTRLA.reg |= TC_CTRLA_WAVEGEN_MFRQ;
//set prescaler and enable TC5
TC5->COUNT16.CTRLA.reg |= TC_CTRLA_PRESCALER_DIV1 | TC_CTRLA_ENABLE;
//set TC5 timer counter based off of the system clock and the user defined sample rate or waveform
TC5->COUNT16.CC[0].reg = (uint16_t) (SystemCoreClock / sampleRate - 1);
while (tcIsSyncing());

// Configure interrupt request
NVIC_DisableIRQ(TC5_IRQn);
NVIC_ClearPendingIRQ(TC5_IRQn);
NVIC_SetPriority(TC5_IRQn, 0);
NVIC_EnableIRQ(TC5_IRQn);

// Enable the TC5 interrupt request
TC5->COUNT16.INTENSET.bit.MC0 = 1;
while (tcIsSyncing()); //wait until TC5 is done syncing 
}

//Function that is used to check if TC5 is done syncing
//returns true when it is done syncing
bool tcIsSyncing()
{
  return TC5->COUNT16.STATUS.reg & TC_STATUS_SYNCBUSY;
}

//This function enables TC5 and waits for it to be ready
void tcStartCounter()
{
  TC5->COUNT16.CTRLA.reg |= TC_CTRLA_ENABLE; //set the CTRLA register
  while (tcIsSyncing()); //wait until snyc'd
}

//Reset TC5 
void tcReset()
{
  TC5->COUNT16.CTRLA.reg = TC_CTRLA_SWRST;
  while (tcIsSyncing());
  while (TC5->COUNT16.CTRLA.bit.SWRST);
}

//disable TC5
void tcDisable()
{
  TC5->COUNT16.CTRLA.reg &= ~TC_CTRLA_ENABLE;
  while (tcIsSyncing());
}

void TC5_Handler (void)
{
  analogWrite(A0, wavSamples[sIndex]);
  sIndex++;
  TC5->COUNT16.INTFLAG.bit.MC0 = 1;
}