DDS Function Generator

This is a new implementation of the AVR DDS signal generator v2.0, already published in scienceprog.com.  It is obvious that full credit for the original schematic and the firmware goes to its original creator. Presented here is a different PCB that is compact, single sided with only through-hole components for easy construction. 

● Parts list

Part	Value
R1	470 Ω ½W 5%
R2	10 ΚΩ ¼W 5%
R3	100 ΚΩ ¼W 1%
R4	20 ΚΩ ¼W 1%
R5	20 ΚΩ ¼W 1%
R6	10 ΚΩ ¼W 1%
R7	20 ΚΩ ¼W 1%
R8	10 ΚΩ ¼W 1%
R9	20 ΚΩ ¼W 1%
R10	10 ΚΩ ¼W 1%
R11	20 ΚΩ ¼W 1%
R12	10 ΚΩ ¼W 1%
R13	20 ΚΩ ¼W 1%
R14	10 ΚΩ ¼W 1%
R15	20 ΚΩ ¼W 1%
R16	10 ΚΩ ¼W 1%
R17	20 ΚΩ ¼W 1%
R18	10 ΚΩ ¼W 1%
R19	20 ΚΩ ¼W 1%
R20	100 Ω ¼W 5%
R21	100 ΚΩ ¼W 1%
R22	12 ΚΩ ¼W 1%
R23	150 Ω ¼W 5%
POT1	1 ΚΩ linear potentiometer
POT2	47 KΩ linear potentiometer
POT3	10 ΚΩ trimmer
C1	100 nF MKT/polyester
C2	100 nF MKT/polyester
C3	18 pF ceramic
C4	18 pF ceramic
Q1	16 MHz crystal
IC1	ATMEL ATMEGA16P
IC2	LM358N
BNC1 – BNC2	BNC female connector
S1 – S6	Push button
LCD Header	Female header 16 pin for LCD
LCD Module	HD44780-based 2×16 character LCD
ISP	Male header 2x3 for ISP
POWER	Female header 4-pin for power as follows : PIN1 : +12V PIN2 : -12V PIN3 : GND PIN4 : +5V
LED1	3 mm green led
ON/OFF	Miniature on/off switch

● Power supply

For powering up the function generator, a PC ATX power supply unit was used, where all voltages are already available (+12V, -12V, +5V). The wiring is shown in the following image, taken from scienceprog.com.

● PCB Making-of

for making of pcb video click here

Programming of the ATMEGA16 with usbtiny programmer 

The device firmware can be downloaded here :

● Changes in firmware

Because of the present LCD character orientation, which is different from the original implementation (180 degrees), the following changes in main.c were made :

Buttons LEFT and RIGHT were reversed :

#define LEFT 3//PORTD

#define RIGHT 1//PORTD

Buttons TOP and BOTTOM were reversed :

#define DOWN 4//PORTD

#define UP 0//PORTD

For the latest version of AVR-GCC compiler, the following changes should be made (according to Geoff comment on scienceprog.com) :

struct signal{

volatile uint8_t mode; //signal

volatile uint8_t fr1; //Frequency [0..7]

volatile uint8_t fr2; //Frequency [8..15]

volatile uint8_t fr3; //Frequency [16..31]

volatile uint32_t freq; //frequency value

volatile uint8_t flag; //if “0″generator is OFF, “1″ – 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 to the following options checked (all others unchecked) :

OCDEN

SPIEN

BOOTSZ1

BOOTSZ2

SUT1

SUT0

Testing