Web Extras, Materials, and Corrections for Volume 35

16 thoughts on “Web Extras, Materials, and Corrections for Volume 35”

1. Jim Jewett says:

   July 21st, 2013 at 11:05 am

   In the digital edition of vol 35, the links to get to the web materials (this web page) seems to be wrong. The link address used at various locations throughout the magazine is makezine.com/35. This forwards me to https://makezine.com/2007/05/30/35-avr-oscilloscope-clock/ which is WAY off-topic.

   FYI

2. Shalom says:

   July 22nd, 2013 at 6:49 pm

   Note for “Advanced Arduino Sound Synthesis” code: in listing_2 line 24, it is recommended that you comment out that line and add v=0 as follows:

   float v=0;//v = (AMP*sin((PI2/LENGTH)*i)); // Calculate current entry

   If you don’t, the square wave that results is half square wave and the other half sine wave. Sort of the Centaur of waveforms!

   Nice job on the article Jon Thompson!

1. Shalom says:

   July 25th, 2013 at 8:27 pm

   I’ve edited the author’s “listing_3” code to output a Sawtooth wave instead of a Square wave and also edited the code so that it more closely resembles the standard Fourier Synthesis Equation. Notice that OFFSET is removed since the term a0*.5 takes care of the offset of the waveform in the standard synthesis equation:

   void additive(void) {
   #define PARTIALS 8
   float harmonic[PARTIALS] = {1,3,5,7,9,11,13,15};
   float amplitude[PARTIALS] = {-.4053,-.0450,-.0162,-.0083,-.005,-.0033,-.0024,-.0018};
   float v;
   float an;
   float a0;
   int i,j;

   // Fourier Synthesis Equation
   // v = a0*.5 + sum{ a_n*cos(2*pi*n*t/T) + b_n*sin(2*pi*n*t/T) }
   // where n is harmonic[j] in this code

   for (int i=0; i<LENGTH; i++) {
   a0=AMP;
   v = a0*.5;
   for (int j=0; j<PARTIALS; j++) {
   an = AMP*amplitude[j];
   v += an*cos((PI2/LENGTH)*(i*harmonic[j]));
   }
   v = constrain(v,0,255);
   wave[i]=byte(v);
   }
   }

3. Steve Carney says:

   August 6th, 2013 at 7:40 pm

   Any status on the Electro Chemical Kid Sub? Looking forward to the details of this project!

4. s_p_e_x says:

   August 24th, 2013 at 6:16 pm

   The “Skill Builder — Advanced Arduino Sound Synthesis” code doesn’t seem to build for Arduino Leonardo.

   I have a SparkFun Pro Micro 5V/16MHz ATMega32u4 board which looks very similar to the Arduino Nano in the article, but with a somewhat different chip.

   I have been using it as a Leonardo (programmed that boot loader onto it). If I choose the Pro Micro I can build the code. If I choose Leonardo, it complains:

   listing_3:25: error: ‘TCCR2A’ was not declared in this scope

   I’m guessing that I need an additional #include? Any ideas?

1. Chuck Benedict says:

   September 23rd, 2013 at 7:17 am

   The registers are different with different chips. I have the old Atmega 8 chips and so modified listing_2 to work. Here is my example:

   /******** Load AVR timer interrupt macros ********/
   #include

   /******** Sine wave parameters ********/
   #define PI2 6.283185 // 2 * PI – saves calculating it later
   #define AMP 127 // Multiplication factor for the sine wave
   #define OFFSET 128 // Offset shifts wave to just positive values

   /******** Lookup table ********/
   #define LENGTH 256 // The length of the waveform lookup table
   byte wave[LENGTH]; // Storage for the waveform

   /******** Waveform parameters ********/
   #define SINE 0
   #define RAMP 1
   #define TRIANGLE 2
   #define SQUARE 3
   #define RANDOM 4

   void setup() {

   /******** Populate the waveform lookup table with a sine wave ********/
   waveform(SINE); // Replace sine with the different cases to
   // Produce the different waves

   /******** Set timer1 for 8-bit fast PWM output ********/
   pinMode(9, OUTPUT); // Make timer’s PWM pin an output
   TCCR1B = (1 << CS10); // Set prescaler to 1 – full 8MHz
   TCCR1A |= (1 << COM1A1); // PWM pin to go low when TCNT1=OCR1A
   TCCR1A |= (1 << WGM10); // Put timer into 8-bit fast PWM mode
   TCCR1B |= (1 << WGM12);

   /******** Set up timer 2 to call ISR ********/
   TCCR2 = (1 << CS20); // Set prescaller to divide by 1
   TIMSK = (1 << OCIE2); // Set timer to call ISR when TCNT2 = OCR2
   OCR2 = 128; // sets the frequency of the generated wave
   // 8Mhz / (OCR2 * 256)…in this case, 244 Hz
   sei(); // Enable interrupts to generate waveform!
   }

   void loop() { // Nothing to do!
   }

   /******** Called every time TCNT2 = OCR2 ********/
   ISR(TIMER2_COMP_vect) { // Called each time TCNT2 == OCR2
   static byte index=0; // Points to successive entries in the wavetable
   OCR1AL = wave[index++]; // Update the PWM output
   TCNT2 = 33; // Timing to compensate for time spent in ISR
   }

   void waveform(byte w) {
   switch(w) {

   case SINE:
   for (int i=0; i<LENGTH; i++)
   {float v = OFFSET+(AMP*sin((PI2/LENGTH)*i));
   wave[i]=int(v);
   }
   break;

   case RAMP:
   for (int i=0; i<LENGTH; i++) {
   wave[i]=i;
   }
   break;

   case TRIANGLE:
   for (int i=0; i<LENGTH; i++) {
   if (i<(LENGTH/2)) {
   wave[i]=i*2;
   } else {
   wave[i]=(LENGTH-1)-(i*2);
   }
   }
   break;

   case SQUARE:
   for (int i=0; i<(LENGTH/2); i++) {
   wave[i]=255;
   }
   break;

   case RANDOM:
   randomSeed(2);
   for (int i=0; i<LENGTH; i++) {
   wave[i]=random(256);
   }
   break;
   }
   }

2. Chuck Benedict says:

   September 25th, 2013 at 5:46 am

   I blogged more about the changes I made using an ATmega8 at http://myrede.blogspot.com/2013/09/advanced-arduino-sound-synthesis.html

5. Dinosorceror says:

   November 12th, 2013 at 11:34 pm

   I’m fairly new to sound synthesis and oscilloscope use, but even after following Shalom’s advice to make the square wave more “square” in listing_2, I’m still not seeing a truly square wave on my scope. It’s vaguely square, but has a sweeping curve up to the peak and then a curve away on the downslope (much like a stereotypical ocean wave). Any ideas?

   Also, I didn’t have an exact match for the transistor specified, I tried using a 2N2222, as well as a BC549, and I couldn’t get any increase in volume on a 8-ohm speaker. In fact, hooking up a scope pretty much showed nothing. I just wound up using an amplified speaker instead, and just kept to the resistor and capacitor.

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