Arduino Duemilanove DAC output is very fluctuating when checked on Oscilloscope

Official Hardware Mega Due
1

I generated Sine wave using Arduino Due on DAC0 pin with the help of a sine lookup table. I tried achieving a frequency of 50 Hz by setting the sampling time of samples as 166.6666667 microseconds. When checked the signal received on DAC output using Oscilloscope, the frequency is wiggling too much and it's not stable. But in my project, I need high precision. Such fluctuations will not serve the cause, how can I make DAC output stable? Please guide through it. Thanks in Advance.

I am also posting my code below: -

#include <DueTimer.h>
#include "Waveforms.h"
volatile int wave0 = 0;
int i = 0;

void myHandler_1()
{
analogWrite(DAC0, waveformsTable_1[wave0]*); *
i++;
if (i == maxSamplesNum)

  • i = 0;*
    }
    void setup()
    {
    Serial.begin(9600);
    analogWriteResolution(12);
    NVIC_SetPriority(TC4_IRQn, 1);
    Timer4.attachInterrupt(myHandler_1).start(166.6666667); // DAC
    }
    void loop()
    {
    }
    Code in Waveforms.h header file
    #ifndef Waveforms_h
    #define Waveforms_h
    #define maxWaveform 1
    #define maxSamplesNum 120
    static int waveformsTable_1[maxWaveform][maxSamplesNum] = {
    {
  • 2047, 2154, 2261, 2367, 2473, 2577, 2680, 2781, 2880, 2977,*
  • 3071, 3162, 3250, 3336, 3417, 3495, 3569, 3638, 3703, 3764,*
  • 3820, 3871, 3917, 3959, 3994, 4025, 4050, 4069, 4083, 4092,*
  • 4095, 4092, 4083, 4069, 4050, 4025, 3994, 3959, 3917, 3871,*
  • 3820, 3764, 3703, 3638, 3569, 3495, 3417, 3336, 3250, 3162,*
  • 3071, 2977, 2880, 2781, 2680, 2577, 2473, 2367, 2261, 2154,*
  • 2047, 1940, 1833, 1727, 1621, 1517, 1414, 1313, 1214, 1117,*
  • 1023, 932, 844, 758, 677, 599, 525, 456, 391, 330,*
  • 274, 223, 177, 135, 100, 69, 44, 25, 11, 2,*
  • 0, 2, 11, 25, 44, 69, 100, 135, 177, 223,*
  • 274, 330, 391, 456, 525, 599, 677, 758, 844, 932,*
  • 1023, 1117, 1214, 1313, 1414, 1517, 1621, 1727, 1833, 1940*
    },
    };
    #endif
2

I wonder how your code actually outputs anything resembling a sine.
You are not giving the waveform steps into analogWrite.

Errors:

  • You are stepping with i instead of wavel
  • i should never be global as it is used as a the default local counter literal
  • You are referencing a int[][] array with only one indirection -> you are not reading the values, but the sub table pointers
3

There is some error coming while uploading the post in this Arduino forum, I've given instruction as
waveformsTable_1 [wave0] [ i ], I am wondering why it's not showing here, why it's uploading it as analogWrite(DAC0, waveformsTable_1[wave0]);

4

If you want to post code, use the Code window (top-left icon)

[i] is treated nicely

If [ i ] is embedded in regular text, it will be interpreted as a start-italics sequence.

David.

5

Ok, thanks for the information, David. :slight_smile:

6

Can you post some Oscilloscope screenshot?

How does the AVREF input look like?
Which kind of distortion o you get?
What is the impedience of the load?