AD9835 Based Sine/Square Wave Function Generator

Figure 1 

A Microchip PIC16F628 is used as the controller chip for this low cost and simple Since/Square wave generator based on the Analog Devices AD9835 Direct Digital Synthesis (DDS) Generator chip.

The design includes 3 pushbuttons and a novel sliding window LED display as it sets the frequency for any range from 1Hz to 10MHz resolution steps. The output frequency is set exactly and crystal locked which effectively does no drift with temperature or time. The DDS chip is a complete 50MHz clock sine wave generator on a single chip.

A sine wave up to 25MHz is generated by the AD9835 clocked at 50MHz but 10MHz was taken as the arbitrary upper limit in order to control and amplify the output waveform quality at this frequency. This gives a large output signal level over a 0 to 10MHz range with a good quality low distortion.

The 3 purposes served by the PIC16F628 microcontroller include controlling the display and switches, sending the necessary control commands to the AD9835 DDS chip, and storing the output frequency in the internal EEPROM. The cost of the system can be lowered by implementing the 4MHz internal RC oscillator.

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