Native DDS Library for Arduino v1.2

This repository contains the NativeDDS library for Arduino. NativeDDS is a software implemented Direct Digital Synthesizer. NativeDDS generates sinusoidal waves for example for use in audio applications, motor drives, sine wave inverters or for a reference frequency source. The library is easy portable to other platforms.

Function

The DDS frequency resolution is 32-bit. This means that the frequency can be tuned in steps of f_update/(2^32), with f_update = 1/timestep (see below). The amplitude resolution can be eight bits or ten bits by choosing the class instances DDS_8bit_xx or DDS_10bit_xx. The eight bit implementation is faster and will be precise enough in most applications.

The following library instance methods are implemented:

• DDS_8bit_1Ch or DDS_10bit_1Ch
• DDS_8bit_2Ch or DDS_10bit_2Ch
• DDS_8bit_IQ or DDS_10bit_IQ
• DDS_8bit_3Ph or DDS_10bit_3Ph

The explanation below will be continued for the 8-bit case.

DDS_8bit_1Ch is a single (output) channel DDS, DDS_8bit_2Ch is a dual channel DDS, DDS_8bit_IQ is a dual channel DDS generating orthogonal outputs and DDS_8bit_3Ph is a three output channel DDS.

The following methods exists:

.begin()

.update()

Initialize the class instance with the member function begin(). Also, begin() must be called each time when the frequency or phase has to be updated.

DDS_8bit_1Ch, use: .begin(float frequency, float starting-phase, float timestep);

DDS_8bit_2Ch, use: .begin(float frequency1, float frequency2, starting-phase1, float starting-phase2, timestep);

DDS_8bit_IQ, use: .begin(float frequency, float starting-phase, float timestep);

DDS_8bit_3Ph, use: .begin(float frequency, float starting-phase, float timestep);

For the member function .begin(), the variable frequency is in Hz and starting-phase in radians. timestep is the loop repeating time in seconds at which .update() is invoked.

The following public output variables are defined:

DDS_8bit_1Ch: out1 and uout1 for unsigned.

DDS_8bit_2Ch: out1, out2 and uout1, uout2 for unsigned.

DDS_8bit_IQ: outi, outq and uouti, uoutq for unsigned.

DDS_8bit_3Ph: outu, outv, outw and uoutu, uoutv, uoutw for unsigned.

Usage

• First create an instance of the library object, for example here we define mySin:

DDS_8bit_1Ch mySine;

• Initialize the DDS on some place in your setup function:

void setup() {
	...
	mySine.begin(float frequency, float starting-phase, float timestep);
	...
}

• Call mySine.update(); from the main loop or from an Interrupt Service Routine (ISR). Use .update(void) on the basis of a regular time interval to generate a jitter free output signal.

Right after the previous step, the instantaneous (unsigned) output value is obtained with: int sample = mySine.uout1;

void loop() {
	...
	mySine.update();
	sample=mySine.uout1
	analogWrite(PWM_OUT, sample);
	...
}

Examples

SineWave_8bit.ino - Example of a single channel 8-bits DDS. The time base is generated in the main loop. The maximum usable output frequency is limited to about 100Hz.

SineWave_10bit.ino - Example of a single channel 10-bits DDS. The time base is generated in the main loop. The maximum usable output frequency is limited to about 100Hz.

WobblingServo.ino - A slowly sine-wave modulated servo motor application.

AudioGenerator.ino - A generator for audible frequencies. A timer interrupt has been used to create the time base.

Acknowledgement

A lot of time was saved in developing this library by using the alternative Arduino-IDE Sloeber. Sloeber is a wonderful Arduino plugin for Eclipse. Thanks to Jantje and his contributors!