A New AVR Signal Generator for Implementing DDS

This is a new implementation of an AVR DDS signal generator V2.0, which has been published on scienceprog.com. Obviously, full credit to its original creators is due for the original schematic and firmware. Presented here is a different PCB, compact and single-sided with through-hole components for easy construction. The function generator has two BNC outputs: one for high speed [1 to 8 MHz] squared signal (BNC1) and another for DDS signal (BNC2). Offset and amplitude can be adjusted with two potentiometers: offset in the range of +5 V to -5 V (POT1) and amplitude in the range of 0 to 10 V (POT2). The up and down arrow buttons are used to change the type of function (sine, trig, etc.), while the left and right arrow buttons are used to change the frequency value. There is also a separate menu for changing the frequency step. When the middle button is pressed, the signal generation starts. Schematic

EAGLE schematic (only one status LED and on/off switch on the shelf)

PCB

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EAGLE PCB (silk screen and bottom layer)

Parts List

power supply

For powering the function generator, a PC ATX power supply was used, with all voltages listed (+12 V, -12 V, +5 V). The wiring is shown in the image below taken from scienceprog.com.

Factory-made printed circuit boards and components

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PCB production

Photo of assembled PCB

ATMEGA16 programmer programming with usbtiny

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Since the orientation of the LCD characters is currently different from the original implementation (180 degrees), the following modifications were made in main.c: The left and right buttons were swapped:

#define LEFT 3 // PORTD

#define RIGHT1 // PORTD

The buttons TOP and BOTTOM are interchanged:

#define FALL 4 // PORTD

#define MAX 0 //PORTD

For recent versions of the AVR-GCC compiler, the following changes should be made (according to Jeff's comment at scienceprog.com):

Structure signal {

volatile uint8_t mode; //signal

unstable uint8_t FR1 //frequency [0..7]

volatile uint8_t FR2; //frequency [8..15]

volatile uint8_t FR3; //frequency [16..31]

volatile uint32_t frequency; //frequency value

oscillate uint8_t flag; //if 0 the generator is off, 1 is on

Volatile uint32_t ACC //Accumulator

volatile uint8_t ON;

volatile uint8_t HSfreq //High speed frequency [1 ... 4Mhz]

Volatile uint32_t deltafreq; //Frequency step value

} SG;

The ATMEGA16 fuses should be:

High = 0 × 59

LOW = 0xCF

This is interpreted as the following options being selected (all others being unchecked):

OCDEN

SPIEN

BOOTSZ1

BOOTSZ2

SUT1

SUT0

Photo equipment

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Final lab setup