DDS based function generators

[MeggerMan]

This topic is to cover the parts required to build a DDS function generator.

Currently I am working on an inverter board for the DDS 20 function generator to provide the -5V rail for the high speed video op amp that produces the sine wave.
This uses the +5V rail from the DDS 20 to power it and after searching for every kind of inverter and dc-dc chip I came up with the TPS6735.

Schematic
http://i100.photobucket.com/albums/m25/kingrs/inverter_schematic_v1-0.jpg

Board
http://i100.photobucket.com/albums/m25/kingrs/inverter_layoutv1-0.jpg

Blanks
http://i100.photobucket.com/albums/m25/kingrs/inverter_pcb_blank_v1.jpg

Built
http://i100.photobucket.com/albums/m25/kingrs/inverter_built_v1.jpg

The output voltage is -4.946 volts at 60mA load with about 10mV of ripple although the scope shows about 18mV of noise anyway so its hard to tell what the real ripple is.
The power required by the op amp is about 25mA.
After struggling with removing the existing components I have decided to re-think the layout and drop the PCB directly onto the main PCB and make use of the existing components. The only component I am not sure about is the 7905 voltage reg. and the question is will the regulator cause a drain on the system in passive mode - if so I will need to cut the track.


Regards
Rob

[MeggerMan]

Testing and tools:

AD9835 placed on some SOIC pads.
http://i100.photobucket.com/albums/m25/kingrs/AD9835_on_tracks.jpg

Testing the -5V inverter with a 65mA load.
http://i100.photobucket.com/albums/m25/kingrs/Inverter_testing.jpg

PCB drill press with Dremel
http://i100.photobucket.com/albums/m25/kingrs/Drill_press.jpg

Konus scope for SMD PCB re-work soldering.
http://i100.photobucket.com/albums/m25/kingrs/Konus20xScope.jpg

Homemade 2 x 8watt UV exposure unit
http://i100.photobucket.com/albums/m25/kingrs/UV_exposure_unit_closed.jpg

UV exposure unit with artwork.
http://i100.photobucket.com/albums/m25/kingrs/UV_exposure_unit_open.jpg

[MeggerMan]

DDS 20 with ali case and collet type knobs (medium on the rotary encoder and small on the sine wave amplitude)
http://i100.photobucket.com/albums/m25/kingrs/DDS20_case_knobs_medium_small.jpg

knobs medium and medium
http://i100.photobucket.com/albums/m25/kingrs/DDS20_case_knobs_medium_medium.jpg

knobs large and medium
http://i100.photobucket.com/albums/m25/kingrs/DDS20_case_knobs_large_medium.jpg

Delay line compared with the AD9959
http://i100.photobucket.com/albums/m25/kingrs/DS1023-100_AD9959.jpg

top view under scope
http://i100.photobucket.com/albums/m25/kingrs/AD9959vSOIC_top.jpg

DS1023-100+ and AD9959
http://i100.photobucket.com/albums/m25/kingrs/AD9959vSOIC.jpg

DIL 8 showing just the narrow tips and AD9959, side view of the AD9959 appears to show the leads as quite wide where the underside view shows a much narrower pad.

http://i100.photobucket.com/albums/m25/kingrs/AD9959vDIL8.jpg

Regards
Rob

[MarkSnoswell]

Very nice Rob -- looks like you are well set up there.

9959 -- Wow -- tiny!

[MeggerMan]

I now have the samples for the PIC16F887 microcontroller. 1 x 40Pin DIP and 3 x 44 pin TQFP (thin square flat package).
I have tested the 40 pin DIP in a breadboard and can confirm that using it with the Pickit 2 flash programmer, I am able to do in circuit debugging in assembler.
Next step is to get the code I found that uses the 16F628 and AD9833 to compile in MPASM IDE and convert to run on the 16F887 and use the AD9959:
Description as follows:

;*************************************************************************
; DDS_F_Gen.asm
;
; Processor: PIC 16F628 Clocked at : 25MHz (EXT Osc) DDS CLOCK
;
; (Re)Coded: 26/03/05 Author :MRB
; Revision tracking: Ver. 1.01 :(1st issue, 1 changes/fixes)
;
;*************************************************************************
; FUNCTIONAL OVERVIEW
;
; A DIRECT DIGITAL SYNTHESIS SINE/TRIANGLE/SQUARE FUNCTION GENERATOR
; 0.0Hz TO 10MHz TO 0.1Hz RESOLUTION
; 0.0 TO 10.0 Vpp OUTPUT RANGE TO 0.1V RESOLUTION
; PUSH BUTTON CONTROL, WITH 2 X 16 LCD
;
; THE WAVEFORM IS SYNTHESISED USING AN ANALOG DEVICES AD9833 SPI DDS IC
; THE OUTPUT LEVEL IS CONTROLLED BY AN DS1267 SPI E-POT
;
;*************************************************************************

; Port A I/O allocation

; PIN DIR USE

; RA0 O/P DDS FUNCTION GENERATOR IC SPI BUS FSYNC (PULLED UP)
; RA1 O/P ELECTRONIC POTENTIOMETER IC SPI BUS FSYNC (PULLED DOWN)
; RA2 O/P LCD R/S
; RA3 O/P LCD EN*
; RA4 I/P NOT USED


; Port B I/O allocation

; PIN DIR USE

; RB0 O/P LCD D4 / ALSO SPI BUS CLOCK
; RB1 O/P LCD D5 / ALSO SPI BUS DATA
; RB2 O/P LCD D6
; RB3 O/P LCD D7
; RB4 I/P SWITCH 1,UP (ACTIVE LOW,PULLED UP)
; RB5 I/P SWITCH 2,DOWN (ACTIVE LOW,PULLED UP)
; RB6 I/P SWITCH 3,LEFT (ACTIVE LOW,PULLED UP)
; RB7 I/P SWITCH 4,RIGHT (ACTIVE LOW,PULLED UP)

;*************************************************************************