Added DDS sample. Fixed pin 11 PWM output, now default (3 works better).

DDS.cpp

@@ -13,19 +13,30 @@ void DDS::start() {
 #ifdef DDS_PWM_PIN_3
   TCCR2A = (TCCR2A | _BV(COM2B1)) & ~(_BV(COM2B0) | _BV(COM2A1) | _BV(COM2A0)) |
          _BV(WGM21) | _BV(WGM20);
+  TCCR2B = (TCCR2B & ~(_BV(CS22) | _BV(CS21))) | _BV(CS20) | _BV(WGM22);
 #else
   // Alternatively, use pin 11
-  TCCR2A = (TCCR2A | _BV(COM2A1)) & ~(_BV(COM2A0) | _BV(COM2B1) | _BV(COM2B0)) |
-       _BV(WGM21) | _BV(WGM20);
+  // Enable output compare on OC2A, toggle mode
+  TCCR2A = _BV(COM2A1) | _BV(WGM21) | _BV(WGM20);
+  //TCCR2A = (TCCR2A | _BV(COM2A1)) & ~(_BV(COM2A0) | _BV(COM2B1) | _BV(COM2B0)) |
+  //     _BV(WGM21) | _BV(WGM20);
+  TCCR2B = _BV(CS20);
 #endif
-  TCCR2B = (TCCR2B & ~(_BV(CS22) | _BV(CS21))) | _BV(CS20) | _BV(WGM22);
 
   // Set the top limit, which will be our duty cycle accuracy.
   // Setting Comparator Bits smaller will allow for higher frequency PWM,
   // with the loss of resolution.
+#ifdef DDS_PWM_PIN_3
   OCR2A = pow(2,COMPARATOR_BITS)-1;
   OCR2B = 0;
+#else
+  OCR2A = 0;
+#endif
   
+#ifdef DDS_USE_ONLY_TIMER2
+  TIMSK2 |= _BV(TOIE2);
+#endif
+
   // Second, setup Timer1 to trigger the ADC interrupt
   // This lets us use decoding functions that run at the same reference
   // clock as the DDS.
@@ -50,16 +61,18 @@ void DDS::stop() {
 void DDS::setFrequency(unsigned short freq) {
   // Fo = (M*Fc)/2^N
   // M = (Fo/Fc)*2^N
-  if(refclk == DDS_REFCLK_DEAULT) {
+  if(refclk == DDS_REFCLK_DEFAULT) {
     // Try to use precalculated values if possible
     if(freq == 2200) {
-      stepRate = (2200.0 / DDS_REFCLK_DEAULT) * pow(2,ACCUMULATOR_BITS);
+      stepRate = (2200.0 / (DDS_REFCLK_DEFAULT+DDS_REFCLK_OFFSET)) * pow(2,ACCUMULATOR_BITS);
     } else if (freq == 1200) {
-      stepRate = (1200.0 / DDS_REFCLK_DEAULT) * pow(2,ACCUMULATOR_BITS);      
+      stepRate = (1200.0 / (DDS_REFCLK_DEFAULT+DDS_REFCLK_OFFSET)) * pow(2,ACCUMULATOR_BITS);      
+    } else if (freq == 600) {
+      stepRate = (600.0 / (DDS_REFCLK_DEFAULT+DDS_REFCLK_OFFSET)) * pow(2,ACCUMULATOR_BITS);      
     }
   } else {
-    // Do the actual math instead.
-    stepRate = (freq / refclk) * pow(2,ACCUMULATOR_BITS);    
+    // BUG: Step rate isn't properly calculated here, it gets the wrong frequency
+    stepRate = (freq/(refclk+DDS_REFCLK_OFFSET)) * pow(2,ACCUMULATOR_BITS);
   }
 }
 
@@ -68,28 +81,40 @@ void DDS::clockTick() {
   if(running) {
     accumulator += stepRate;
     if(timeLimited && tickDuration == 0) {
+#ifndef DDS_PWM_PIN_3
+      OCR2A = 0;
+#else
 #ifdef DDS_IDLE_HIGH
       // Set the duty cycle to 50%
       OCR2B = pow(2,COMPARATOR_BITS)/2;
 #else
       // Set duty cycle to 0, effectively off
       OCR2B = 0;
+#endif
 #endif
       running = false;
       accumulator = 0;
     } else {
+#ifdef DDS_PWM_PIN_3
       OCR2B = getDutyCycle();
+#else
+      OCR2A = getDutyCycle();
+#endif
     }
     // Reduce our playback duration by one tick
     tickDuration--;
   } else {
     // Hold it low
+#ifndef DDS_PWM_PIN_3
+    OCR2A = 0;
+#else
 #ifdef DDS_IDLE_HIGH
     // Set the duty cycle to 50%
     OCR2B = pow(2,COMPARATOR_BITS)/2;
 #else
     // Set duty cycle to 0, effectively off
     OCR2B = 0;
+#endif
 #endif
   }
 }

DDS.h

@@ -4,8 +4,14 @@
 #include <avr/pgmspace.h>
 
 // Use pin 3 for PWM? If not defined, use pin 11
+// Quality on pin 3 is higher than on 11, as it can be clocked faster
+// when the COMPARATOR_BITS value is less than 8
 // #define DDS_PWM_PIN_3
 
+// Normally, we turn on timer2 and timer1, and have ADC sampling as our clock
+// Define this to only use Timer2, and not start the ADC clock
+// #define DDS_USE_ONLY_TIMER2
+
 // Use a short (16 bit) accumulator. Phase accuracy is reduced, but speed
 // is increased, along with a reduction in memory use.
 #define SHORT_ACCUMULATOR
@@ -27,16 +33,29 @@
 // 8 = 62.5kHz PWM
 // 7 = 125kHz PWM
 // 6 = 250kHz PWM
+#ifdef DDS_PWM_PIN_3
 #define COMPARATOR_BITS       6
+#else // When using pin 11, we always want 8 bits
+#define COMPARATOR_BITS       8
+#endif
 
 // This is how often we'll perform a phase advance, as well as ADC sampling
 // rate. The higher this value, the smoother the output wave will be, at the
 // expense of CPU time. It maxes out around 62000 (TBD)
-#define DDS_REFCLK_DEAULT     38400
+#define DDS_REFCLK_DEFAULT     38400
+// As each Arduino crystal is a little different, this can be fine tuned to
+// provide more accurate frequencies. Adjustments in the range of hundreds
+// is a good start.
+#define DDS_REFCLK_OFFSET     0
+
+#ifdef DDS_USE_ONLY_TIMER2
+// TODO: Figure out where this clock value is generated from
+#define DDS_REFCLK_DEFAULT     48800
+#endif
 
 // When defined, use the 1024 element sine lookup table. This improves phase
 // accuracy, at the cost of more flash and CPU requirements.
-#define DDS_TABLE_LARGE
+// #define DDS_TABLE_LARGE
 
 #ifdef DDS_TABLE_LARGE
 // How many bits to keep from the accumulator to look up in this table
@@ -131,7 +150,9 @@ static const uint8_t ddsSineTable[256] PROGMEM = {
 
 class DDS {
 public:
-  DDS(): refclk(DDS_REFCLK_DEAULT), accumulator(0), running(false) {};
+  DDS(): refclk(DDS_REFCLK_DEFAULT), accumulator(0), running(false),
+    timeLimited(false), tickDuration(0), amplitude(0)
+    {};
 
   // Start all of the timers needed
   void start();

examples/DDS/DDS.ino

@@ -0,0 +1,32 @@
+#include <HamShield.h>
+#include <Wire.h>
+
+DDS dds;
+
+void setup() {
+  pinMode(2, OUTPUT);
+  pinMode(3, OUTPUT);
+  pinMode(11, OUTPUT);
+  dds.start();
+  dds.setFrequency(440);
+  dds.on();
+  delay(5000);
+}
+
+void loop() {
+  dds.setFrequency(2200);
+  delay(5000);
+  dds.setFrequency(1200);
+  delay(5000);
+}
+
+#ifdef DDS_USE_ONLY_TIMER2
+ISR(TIMER2_OVF_vect) {
+  dds.clockTick();
+}
+#else // Use the ADC timer instead
+ISR(ADC_vect) {
+  TIFR1 = _BV(ICF1); // Clear the timer flag
+  dds.clockTick();
+}
+#endif