DDS Up and running

[Terry Fox]

Just a note to let you know that the first DDS module is up and
running.  I built a simple breadboard around the module, and tickled it
into working the first time!!

As a reminder, it is a Analog Devices AD9832 and 25MHz oscillator
sitting on a small board that mounts onto a 24-pin DIP header.  It can
be programmed (via 3 wires) from almost 0 to about 9 MHz in .025Hz
steps.  I use bits D0, D1, and D2 of the printer port as clock, data,
and select lines.  In addition, it has 2 frequency registers selectable
by software or a hardware pin, and 4 phase registers, also selectable by
software or 2 pins.  FSK, BPSK, or QPSK is easily achievable.

The module generates about 1V P-P, and it does not include a low-pass
filter.  For simple applications, I have used a 5-pole LP filter, and an
Analog Devices AD818 op-amp buffer.  If I want a square wave, I raise
the gain of the op-amp and feed it to a schmidt trigger.

I have enough parts to make about 10 modules, and think the parts are
still around $25.00.  I will put some more together, and prepare some
simple documentation.  Anyone interested in writing software?????

I can think of a lot of applications, and software to write.  RF
sweeper, FSK or PSK generator, etc.  I will also use them for the LO on
my LF receivers.  Remember, the hard part is done, the rest is only
software!

Terry.