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DDS Function Generator
author: Vassilis Papanikolaou - vpapanikgmail.com


 
a new implementation of the AVR DDS signal generator v2.0 found at : 

http://www.scienceprog.com/avr-dds-signal-generator-v20

by Vassilis Papanikolaou (vpapanikgmail.com)

Introduction


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.

The function generator features two BNC outputs : one for the high speed [1 to 8 MHz] square signal (BNC1) and another for the DDS signal (BNC2). Offset and amplitude can be regulated by two potentiometers : offset in range of +5V to -5V (POT1) and amplitude in range of 0 to 10V (POT2). Up and down arrow buttons are used for changing the function type (sine, triangle etc.) while left and right arrow buttons are used for changing the frequency value. There is also a separate menu for changing frequency step. When the middle button is pressed, the signal generation starts. Middle button is pressed again for stopping the signal. More details can be found in the original site.


Schematic


EAGLE Schematic (only a status led and an on/off switch was added)

click on image for higher resolution

 

PCB






EAGLE PCB (silkscreen and bottom layer)

Parts List



Part

Value

R1

470 W 5%

R2

10 ¼W 5%

R3

100 ¼W 1%

R4

20 ¼W 1%

R5

20 ¼W 1%

R6

10 ¼W 1%

R7

20 ¼W 1%

R8

10 ¼W 1%

R9

20 ¼W 1%

R10

10 ¼W 1%

R11

20 ¼W 1%

R12

10 ¼W 1%

R13

20 ¼W 1%

R14

10 ¼W 1%

R15

20 ¼W 1%

R16

10 ¼W 1%

R17

20 ¼W 1%

R18

10 ¼W 1%

R19

20 ¼W 1%

R20

100 ¼W 5%

R21

100 ¼W 1%

R22

12 ¼W 1%

R23

150 ¼W 5%

POT1

1 linear potentiometer

POT2

47 K linear potentiometer

POT3

10 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.





Photos of factory-made PCB and parts








PCB Making-of






Photos of assembled PCB
















Programming of the ATMEGA16 with usbtiny programmer







The device firmware can be downloaded from : 

http://www.scienceprog.com/avr-dds-signal-generator-v20


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 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 to the following options checked (all others unchecked) :

OCDEN
SPIEN
BOOTSZ1
BOOTSZ2
SUT1
SUT0


Photos of the device operation

















Final lab setup






Download



 
 

 
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