Hello Lowfers,

I am currently looking into a way how to realize a simple way of doing FSK
with my DDS VFO. The VFO consists of a AD9850 chip that generates the
frequency. This chips is getting it's information from a PIC that was
programmed by the supplier of the entire unit (S&S Engineering). So I have
no source code nor the ability to re-program the PIC.

The frequency adjustment is realized by a rotary shift encoder. I can set
the freqency up or down movement by digit, e.g. 1 Hz, 10 Hz, 100 Hz and so
forth.

Now my simple question is: how can I simulate a rotary shift decoder in a
simple manner, so that when I key, the freqency is for example 10 Hz higher
and then moves down again to the original frequency. I have no idea how
this is normally realized with the shift encoder, however, I saw that a 5V
signal is simply pulled to ground over a resistor. If I just key one of
those encoder port to ground, I already get the frequency shift keying I
need, however, after keying a couple of times down, the freqnecy is moving
up or down (in those 10Hz jumps). What I need, I assume, is a kind of time
sequence to simulate the rotary shift encoder first into one direction and
then to the other.

Using this method would easily allow me to FSK Slow-CW and, maybe with a
shift of 100 Hz, normal 45.45 bd RTTY.

Anybody has got a simple idea?

Thanks, vy 73