Sawtooth wave with Arduino Uno

Using Arduino Audio
1

Hello everyone,

I'm trying to make a synthesizer (or something like that) by only using an Arduino Uno and a passive buzzer (and no libary for the Arduino).
I know that the most used sound of a synthesizer a sawtooth sound wave is.
I also have a sound file whith a sawtooth sound that is not pitched (I got the sound from an app on my tablet called "FL Studio Mobile" where you can create music with synthesizers).
I have tried this code, but the sound is not similar to the sound file;

int a = 0;

void setup(){
    pinMode(A0, OUTPUT); // The passive buzzer
}

void loop(){
    while(a < 256){
        analogWrite(A0, a);
        delayMicroseconds(10);
        a++;
    }
    a = 0;
}

I think that the problem could be the delayMicroseconds or the condition of the while loop.
Could somebody please help me?
if you have the solution, I would also like to know how to pitch the sound.

2

Your main problem is that the Arduino doesn't have a true-analog output (there is no DAC). analogWrite() is [u]PWM[/u]. That's good enough to control the speed of a motor or to make an LED appear dim, but it's a digital pulse.

There is a [u]TMRpcm[/u] library that uses fast-PWM for audio, but you should probably add a DAC.

3

Running 8-bit PWM at full speed gives a PWM frequency of 62.5kHz on a 16MHz processor, enough
for audio.

In fact you can use noise-shaping too to get more than 8 bits at lower frequencies from the self-same
PWM output.

See this thread:

https://forum.arduino.cc/index.php?topic=455680.0

The advantage of using PWM over a DAC is direct class-D amplification is possible without any
analog stages.

4

I have tried this code, but the sound is not similar to the sound file;

One reason for this is you do not have proper speaker but only a buzzer. These tend not to respond to waves other than pulsed, square and so on.

You can’t do an analogWrite to the A0 pin. It is not capable of it.
You can only use PWM capable outputs for analog write, those are the ones with a tilda, the ~ symbol by their names. It is really a bad name, but the analog write only produces a PWM signal which can only become analog when you have filtered it.

Anyway to actually use it in the way you have the code, you have to set the PWM speed to something fast like 40KHz or so before you try and set the PWM duty cycle.

5

Sorry for my late reaction.

DVDdoug:
There is a [u]TMRpcm[/u] library that uses fast-PWM for audio, but you should probably add a DAC.

I have found [u]this[/u] video where someone is making his own DAC by using resistors and arduino digital pins.
Can i use this for now to test the sound?
I also have searched for a 8 bit DAC component but i can only find 12 bit DAC's such as the mcp4725.
The only thing is that the arduino UNO is not 12 bit.
Is that a problem?

Grumpy_Mike:
One reason for this is you do not have proper speaker but only a buzzer

Thanks for telling me that.
I didn't knew that.

6

I have found this video where someone is making his own DAC by using resistors and arduino digital pins.
Can i use this for now to test the sound?

I didn't watch the video but yes you can make a resistor-ladder DAC.

Resistor tolerance can become an issue, especially as you go beyond 8-bits, but it will work.

I also have searched for a 8 bit DAC component but i can only find 12 bit DAC's such as the mcp4725.
The only thing is that the arduino UNO is not 12 bit.
Is that a problem?

Not a problem. The Arduino "processes" 8-bits at a time but it can handle 16-bit or 32-bit integers, etc. (That makes it slower than a 16 or 32-bit processor.)

The Arduino's ADC is 10-bits and it's read as 16-bit integer (with the 6 most-significant bits always zero).

...I was confused about that when I was first learning about digital too. Someone told me about a computer interface for test equipment that was 8-bits and I said, "8-bits? You can't get any resolution with 8-bits!" But, computer files are written as bytes (8 bits) and everything sent over the Internet is split into bytes so it very common.

7

I finally got a DAC.
It is a MCP4725.
I have already tried a code, but the frequentie is too low.
This is the code:

/****************************************************************************** 
MCP4725 Example Waveform Sketch
Joel Bartlett
SparkFun Electronics
Sept. 11, 2014
https://github.com/sparkfun/MCP4725_Breakout

This sketch takes data from a lookup table to provide 
waveforms to be generated by the MCP4725 DAC. 

Development environment specifics:
Arduino 1.0+
Hardware Version V14

This code is beerware; if you see me (or any other SparkFun employee) at the local, 
and you've found our code helpful, please buy us a round!

Distributed as-is; no warranty is given. 

This code builds off the sketch written by Mark VandeWettering, which can be found here:
http://brainwagon.org/2011/02/24/arduino-mcp4725-breakout-board/
*/

#include <Wire.h>//Include the Wire library to talk I2C

//This is the I2C Address of the MCP4725, by default (A0 pulled to GND).
//Please note that this breakout is for the MCP4725A0. 
#define MCP4725_ADDR 0x60   
//For devices with A0 pulled HIGH, use 0x61

//Sinewave Tables were generated using this calculator:
//http://www.daycounter.com/Calculators/Sine-Generator-Calculator.phtml


int lookup = 0;//varaible for navigating through the tables

int sintab2[512] = 
{
 2048, 2073, 2098, 2123, 2148, 2174, 2199, 2224,
 2249, 2274, 2299, 2324, 2349, 2373, 2398, 2423,
 2448, 2472, 2497, 2521, 2546, 2570, 2594, 2618,
 2643, 2667, 2690, 2714, 2738, 2762, 2785, 2808,
 2832, 2855, 2878, 2901, 2924, 2946, 2969, 2991,
 3013, 3036, 3057, 3079, 3101, 3122, 3144, 3165,
 3186, 3207, 3227, 3248, 3268, 3288, 3308, 3328,
 3347, 3367, 3386, 3405, 3423, 3442, 3460, 3478,
 3496, 3514, 3531, 3548, 3565, 3582, 3599, 3615,
 3631, 3647, 3663, 3678, 3693, 3708, 3722, 3737,
 3751, 3765, 3778, 3792, 3805, 3817, 3830, 3842,
 3854, 3866, 3877, 3888, 3899, 3910, 3920, 3930,
 3940, 3950, 3959, 3968, 3976, 3985, 3993, 4000,
 4008, 4015, 4022, 4028, 4035, 4041, 4046, 4052,
 4057, 4061, 4066, 4070, 4074, 4077, 4081, 4084,
 4086, 4088, 4090, 4092, 4094, 4095, 4095, 4095,
 4095, 4095, 4095, 4095, 4094, 4092, 4090, 4088,
 4086, 4084, 4081, 4077, 4074, 4070, 4066, 4061,
 4057, 4052, 4046, 4041, 4035, 4028, 4022, 4015,
 4008, 4000, 3993, 3985, 3976, 3968, 3959, 3950,
 3940, 3930, 3920, 3910, 3899, 3888, 3877, 3866,
 3854, 3842, 3830, 3817, 3805, 3792, 3778, 3765,
 3751, 3737, 3722, 3708, 3693, 3678, 3663, 3647,
 3631, 3615, 3599, 3582, 3565, 3548, 3531, 3514,
 3496, 3478, 3460, 3442, 3423, 3405, 3386, 3367,
 3347, 3328, 3308, 3288, 3268, 3248, 3227, 3207,
 3186, 3165, 3144, 3122, 3101, 3079, 3057, 3036,
 3013, 2991, 2969, 2946, 2924, 2901, 2878, 2855,
 2832, 2808, 2785, 2762, 2738, 2714, 2690, 2667,
 2643, 2618, 2594, 2570, 2546, 2521, 2497, 2472,
 2448, 2423, 2398, 2373, 2349, 2324, 2299, 2274,
 2249, 2224, 2199, 2174, 2148, 2123, 2098, 2073,
 2048, 2023, 1998, 1973, 1948, 1922, 1897, 1872,
 1847, 1822, 1797, 1772, 1747, 1723, 1698, 1673,
 1648, 1624, 1599, 1575, 1550, 1526, 1502, 1478,
 1453, 1429, 1406, 1382, 1358, 1334, 1311, 1288,
 1264, 1241, 1218, 1195, 1172, 1150, 1127, 1105,
 1083, 1060, 1039, 1017,  995,  974,  952,  931,
  910,  889,  869,  848,  828,  808,  788,  768,
  749,  729,  710,  691,  673,  654,  636,  618,
  600,  582,  565,  548,  531,  514,  497,  481,
  465,  449,  433,  418,  403,  388,  374,  359,
  345,  331,  318,  304,  291,  279,  266,  254,
  242,  230,  219,  208,  197,  186,  176,  166,
  156,  146,  137,  128,  120,  111,  103,   96,
   88,   81,   74,   68,   61,   55,   50,   44,
   39,   35,   30,   26,   22,   19,   15,   12,
   10,    8,    6,    4,    2,    1,    1,    0,
    0,    0,    1,    1,    2,    4,    6,    8,
   10,   12,   15,   19,   22,   26,   30,   35,
   39,   44,   50,   55,   61,   68,   74,   81,
   88,   96,  103,  111,  120,  128,  137,  146,
  156,  166,  176,  186,  197,  208,  219,  230,
  242,  254,  266,  279,  291,  304,  318,  331,
  345,  359,  374,  388,  403,  418,  433,  449,
  465,  481,  497,  514,  531,  548,  565,  582,
  600,  618,  636,  654,  673,  691,  710,  729,
  749,  768,  788,  808,  828,  848,  869,  889,
  910,  931,  952,  974,  995, 1017, 1039, 1060,
 1083, 1105, 1127, 1150, 1172, 1195, 1218, 1241,
 1264, 1288, 1311, 1334, 1358, 1382, 1406, 1429,
 1453, 1478, 1502, 1526, 1550, 1575, 1599, 1624,
 1648, 1673, 1698, 1723, 1747, 1772, 1797, 1822,
 1847, 1872, 1897, 1922, 1948, 1973, 1998, 2023
};


void setup()
{
 Wire.begin();

 // Set A2 and A3 as Outputs to make them our GND and Vcc,
 //which will power the MCP4725
 pinMode(A2, OUTPUT);
 pinMode(A3, OUTPUT);

 digitalWrite(A2, LOW);//Set A2 as GND
 digitalWrite(A3, HIGH);//Set A3 as Vcc
}
//---------------------------------------------------
void loop()
{
 Wire.beginTransmission(MCP4725_ADDR);
 Wire.write(64);                     // cmd to update the DAC
 Wire.write(sintab2[lookup] >> 4);        // the 8 most significant bits...
 Wire.write((sintab2[lookup] & 15) << 4); // the 4 least significant bits...
 Wire.endTransmission();
 lookup = (lookup + 1) & 511;
}

I have a oscilloscope at home and for what I can see was that the frequentie was 1.3Hz.
I'm also trying to understand what the Arduino exactly writes to the DAC and how fast it goes.
If there is a libary for this, I would be happy.
Again, sorry for my late reaction.
btw. Merry Christmas and a Happy New Year :).

8

// Set A2 and A3 as Outputs to make them our GND and Vcc,
//which will power the MCP4725

No no no! Never power anything like this.

The big problem is your device is only I2C, that only transfers data at 100K bits per,second, that is 10K bytes per second. Then you have a 512 byte look up table, so if everything was as fast as it could be you would get only 5 Hz. But then you are writing three bytes per sample which divides that by three to give 1.6 Hz which is close to what you are seeing.

Basically it is the wrong sort of interface to the D/A. You need one that uses SPI.

9

If you want to speed things up then increment the point in the lookup table by more than one.

Better still is to have the pointer as a float value and increment it by a float value. Then the increment value determines the frequency to quite accurate values.

10

Grumpy_Mike:
Basically it is the wrong sort of interface to the D/A. You need one that uses SPI.

Would the MCP4922 be good then?
The interface of it is ISP and it is pretty fast (for what I have read about it).

11

Yes it would be a lot better, the interface is SPI by the way.

However it has two D/As in it and you only need one. So you could probably get a cheaper one.

12

Grumpy_Mike:
However it has two D/As in it and you only need one.

Do they work separately? If so, can I make stereo sound when I have 2 speakers?

13

Yes they do work separately and yes you could use it for stero but this will halve the number of samples per seconds you will be able to acheave.