DDS VFO

Build a PIC controlled DDS VFO, 0 to 6 MHz

Click a picture to zoom

Files contained in MINIDDS.ZIP:

readme.txt	Read this first!
compplac.pdf	Component placement in PDF format
schema.pdf	Schematic diagram in PDF format
top.ps	PCB top copper layer in Postscript format
bottom.ps	PCB bottom copper layer in Postscript format
ad9832_4.asm	PIC assembly source code
p16f84.inc	Needed for assembly of ad9832_4.asm (for 'F84)
p16c84.inc	As above but for 'C84
vfo5x7f.hex	PIC16F84 program for LCD with 5x7 font
vfo5x10f.hex	PIC16F84 program for LCD with 5x10 font
vfo5x7c.hex	PIC16C84 program for LCD with 5x7 font
vfo5x10c.hex	PIC16C84 program for LCD with 5x10 font
filtresp.pcx	Computed frequency response of lowpass filter

Download MINIDDS.ZIP (186K)

If you prefer to control the DDS module from a PC (instead of using a PIC), try this:

Download PCVFO.ZIP (18K)

The zip archive contains a single file, VFO.EXE. It is a DOS program but it runs fine in a Windows 95/98 "DOS bubble" as well (see screenshots above).

Are you looking for a DDS based 136 kHz longwave transmitter exciter?

Have a look at G0MRF's page

Specifications:

Start-up frequency: 137.00000 kHz
Tuning range: 135.70000 to 137.80000 kHz in 0.25 Hz steps
DFCW offset: 0 to 50 Hz adjustable in 0.25 Hz steps
The dial can be locked to prevent inadvertent QSY
Calibration: +/- 200 ppm, stored in EEPROM.
Actual DDS output frequency is 4 * dial frequency

Schematic and source code for the PIC controller is available here:

Download the PIC program lwex.zip

The PIC program is written for the free version of the CC5X C compiler which is available at www.bknd.com

Click the schematic for a full size version

Almost any 2x16 character LCD module with Hitachi HD44780 controller chip will work. The LCD pin numbers on the schematic are not valid for all LCD modules. Please check the actual signal names on your particular LCD module.

The selected DFCW frequency offset will be added to the output frequency when the DFCW input is grounded. This input has a weak pull-up in the PIC.

The encoder inputs also have internal pull-ups in the PIC.

The switches "LOCK", "DFCW" and "CAL" are momentary pushbuttons.

Original scheme from http://home4.swipnet.se/~w-41522/index.html