Based on Analog Device DDS chip AD9832 which is controlled by a PIC16F84. The VFO is separated into two modules, the DDS module and the controller module.
The smallest step size is 1 Hz (although the AD9832 is able to tune in 5.8 mHz (millihertz!) steps). The PIC interfaces to a standard 1×16 LCD which is run in 4-bit
mode. Almost any LCD with Hitachi HD44780 controller will work.
The PIC program is a prototype. Some of the code has been borrowed from another DDS control program (for AD9850) written by Curtis W. Preuss, WB2V. The current version has the following functions:
?- Rotary encoder input for tuning
?- Dial lock switch
?- Step size switch (1, 10, 100, 1 kHz, 10 kHz)
?- LCD interface, shows frequency (in Hz) and step size
?- f/4 display possible (for I/Q front ends using LO divider)
Since the PIC controller is not onboard the DDS module, there is no reason why you couldn’t use, for example, your PC to control the DDS through the printer port. Only three lines are needed to control the AD9832. Have a look at the AD9832 data sheet for detailed information. (Available in PDF format from http://www.analog.com). AD9850 and AD9851 data sheets are also worth reading for general DDS information.
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