[sdiy] Controller design

[mskala at ansuz.sooke.bc.ca]

On Tue, 29 Dec 2015, Chris Juried wrote:
> Using individual, fixed frequency, tuned oscillators is what came to my mind
> as well. What do you propose for a summing network? Thanks!

My understanding is that there are supposed to be 10 buttons, each of
which has two fixed frequencies (one for one bellows direction, the other
for the other).  It seems like the simplest thing would be to make the
buttons be DPST switches; 20 oscillators feed into the buttons (two to
each button), then an op amp adder circuit for each direction sums the
switched signals (one sums all the selected "in" signals from the buttons,
the other all the selected "out" signals), and whatever senses the bellows
direction can switch between the two op amps.  The op amp (inverting)
adder is just a resistor from each button output to the op amp's negative
input, one from the output to the negative input, and the positive input
grounded.

If using DPST switches for the buttons is a problem, one could switch
between the oscillators upstream of the buttons, but that means having 10
SPDT electronic switches of some kind, which is probably more complicated
than just using the buttons to switch pairs of oscillator signals.

Twenty oscillators may sound like a lot, but if they're fixed-frequency,
they're much easier to build than 4 stable VCOs and the control circuitry
to manipulate the control voltages.  If any of the "in" frequencies
coincide with "out" frequencies, there may be some opportunity to share
oscillators between the two and bring the total count down.

-- 
Matthew Skala
mskala at ansuz.sooke.bc.ca                 People before principles.
http://ansuz.sooke.bc.ca/