* Timer2 generates the 31250 KHz Clock Interrupt The frequency appears on pin 11 where you can connect active speakers or an output filter described later. To run this software on an Arduino Diecimila or Duemilenove connect a potentiometer to +5Volt and Ground and the wiper to analog 0. MT-085: Fundamentals of Direct Digital Synthesis (DDS) This article published by Analog Devices is one of many good references. Further details of the DDS Method are described in web of course. The whole process is cycle timed by an interrupt process which acts as the reference clock. To the accumulator, the tuning word is added, the most significant byte of the accu is taken as address of the sinetable where the value is fetched and outputted as analog value bye the PWM unit.

An accumulator and a tuning word which are in our case just two long integer variables, a sinewave table as a list of numerical values of one sine period stored as constants, a digital analog converter which is provided by the PWM (analogWrite) unit, and a reference clock derived by a internal hardware timer in the atmega. To implement the DDS Method in software we need four components. The DDS Method (digital direct synthesis) Also in telecommunication the DDS Method is useful for instance in frequency of phase modulation (FSK PSK). This technique is not only useful for music and sound generation another range of application is test equipment or measurement instrumentation. The frequency range reaches form zero to 16 KHz with a resolution of a millionth part of one Hertz! Distortions can be kept less than one percent on frequencies up to 3 KHz. Almost no additional hardware is required.

Here we describe how to generate sine waves with an Arduino board in a very accurate way. Arduino Sine wave Generator using the direct digital synthesis Method

Pgmspace.h arduino simulator