During my spare time I am developing the program for AVR controlled DDS generator. I decided to write software using WinAVR tool-set. How far ahead I have moved with this?

I have implemented:

• Menu system;
• Reading previous generator configuration from EEPROM;
• Setting signal mode;
• Storing last generator configuration to EEPROM to be loaded after reset;
• Four types of signal output (square, sawtooth, triangle and sine wave);

Still need to do:

• Ability to change signal frequency;
• Implement other signals (listed bellow);
• Make program clean-up;

Signals in AVR controlled generator:

• 0 – OUT_|¯|_ - square wave(done);
• 1 – OUT|/|/| - sawtooth(done);
• 2 – OUT|\|\| - reverse sawtooth(awaiting);
• 3 – OUT/\/\/\ - triangle(done);
• 4 – OUT~~~~ - sine wave(done);
• 5 – OUT-NOISE – noise signal(awaiting);
• 20 – PWM-OCC – timer output compare mode(awaiting);
• 21 – PWM-SINMDS – sine wave modulated PWM(awaiting);
• 22 – PWMSQSMDS - sine wave modulated PWM. PWM positive, SQ – negative polarity(awaiting);
• 23 – PWM-CMDS – custom PWM. Will be possible to set custom duty cycle(awaiting);

Signal generation

Square, sawtooth, triangle and sine waves are generated by reading values from flash memory. Fragment of sine wave is as follows:

//———————————————–

//signals saved in flash memory

const uint8_t sinewave[] PROGMEM= //256 values

{

0×80,0×83,0×86,0×89,0×8c,0×8f,0×92,0×95,0×98,0×9c,0×9f,0xa2,0xa5,0xa8,0xab,0xae,

0xb0,0xb3,0xb6,0xb9,0xbc,0xbf,0xc1,0xc4,0xc7,0xc9,0xcc,0xce,0xd1,0xd3,0xd5,0xd8,

0xda,0xdc,0xde,0xe0,0xe2,0xe4,0xe6,0xe8,0xea,0xec,0xed,0xef,0xf0,0xf2,0xf3,0xf5,

0xf6,0xf7,0xf8,0xf9,0xfa,0xfb,0xfc,0xfc,0xfd,0xfe,0xfe,0xff,0xff,0xff,0xff,0xff,

0xff,0xff,0xff,0xff,0xff,0xff,0xfe,0xfe,0xfd,0xfc,0xfc,0xfb,0xfa,0xf9,0xf8,0xf7,

0xf6,0xf5,0xf3,0xf2,0xf0,0xef,0xed,0xec,0xea,0xe8,0xe6,0xe4,0xe2,0xe0,0xde,0xdc,

0xda,0xd8,0xd5,0xd3,0xd1,0xce,0xcc,0xc9,0xc7,0xc4,0xc1,0xbf,0xbc,0xb9,0xb6,0xb3,

0xb0,0xae,0xab,0xa8,0xa5,0xa2,0×9f,0×9c,0×98,0×95,0×92,0×8f,0×8c,0×89,0×86,0×83,

0×80,0×7c,0×79,0×76,0×73,0×70,0×6d,0×6a,0×67,0×63,0×60,0×5d,0×5a,0×57,0×54,0×51,

0×4f,0×4c,0×49,0×46,0×43,0×40,0×3e,0×3b,0×38,0×36,0×33,0×31,0×2e,0×2c,0×2a,0×27,

0×25,0×23,0×21,0×1f,0×1d,0×1b,0×19,0×17,0×15,0×13,0×12,0×10,0×0f,0×0d,0×0c,0×0a,

0×09,0×08,0×07,0×06,0×05,0×04,0×03,0×03,0×02,0×01,0×01,0×00,0×00,0×00,0×00,0×00,

0×00,0×00,0×00,0×00,0×00,0×00,0×01,0×01,0×02,0×03,0×03,0×04,0×05,0×06,0×07,0×08,

0×09,0×0a,0×0c,0×0d,0×0f,0×10,0×12,0×13,0×15,0×17,0×19,0×1b,0×1d,0×1f,0×21,0×23,

0×25,0×27,0×2a,0×2c,0×2e,0×31,0×33,0×36,0×38,0×3b,0×3e,0×40,0×43,0×46,0×49,0×4c,

0×4f,0×51,0×54,0×57,0×5a,0×5d,0×60,0×63,0×67,0×6a,0×6d,0×70,0×73,0×76,0×79,0×7c

};

//———————————————–

The same is with square, sawtooth and triangle. Each wave is stored using 256 value table.

Signal is generated using simple function:

//———————————————–

void signalOUT(const uint8_t *signal)

{

uint8_t i;

i=0;

do

{

PORTD=pgm_read_byte(&signal[i++]);

}while(1);

}

//———————————————–

Using this function the maximum generated signal frequency was 6,25kHz. This means that one signal period consists of 256 values from signal table. Crystal frequency is 16MHz. So for one value from table it requires 16000000/(6250*256)=10 clock cycles.

Changing frequency of those signals should be ease. Just insert inside loop delay function regarding to selected frequency. This I will do later.

I still don’t know is it worse to try increase maximum frequency of signal. Now it is 6,25kHz and takes 10 clock cycles for one byte from 256 to output. If I would reach 5 cycles, that would be double frequency 12,5kHz.

In other hand if greater frequencies are needed there will be possibility to use timer signal generator on output compare mode, but only square waves.

Now I going to focus on implementing what I have planned and then think about optimisation.

Bellow are signal pictures I have got at frequency 6,25kHz(picture quality is poor - I really need to get tripod for my camera):

Square

Sawtooth

Triangle

Sine wave

The source code of current program is here:AVR controlled DDS generator software

Full documentation is on its way.

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This entry was posted on Wednesday, June 21st, 2006 at 11:30 pm and is filed under AVR controlled signal generator. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.