[sdiy] undertstanding switches/muxes in a multi mode/preset setup

[johnspeth at yahoo.com]

Think for a moment, if you would ask the same question if the caps were not there.  The SW1A and SW1B switches are user controls that set the mux's A and B logic levels.  The capacitors (C1-C4) appeared to be there to soften the switching transients of the switches.  I'm not sure they're even needed, but I never built the circuit.  They're probably there to lessen audio pops during switching.

Let's pretend to take the caps out for analysis sake.  The A,B inputs will either be pulled high using the pull ups or at ground depending on the switch positions.  Adding the caps now, simply affects the switching voltage profiles.  During DC mode (switches not changing), the caps do nothing.  It's that simple.

JJS


----- Original Message ----
> can anyone help me understand what is going on in the switching section of this 
> schematic?
> 
> http://www.freeinfosociety.com/media.php?id=675
> 
> i know how a 4052 works and i can see that there are multiple filters, but 
> something about how the wires are drawn, i am confused as to how the switch is 
> changing modes.
> 
> i see the pullup resistors, but it looks like the A and B are Always connected 
> to ground through a cap.
> 
> any help would be greatly appreciated.
> 
> and actually, if anyone could recommend any other synth circuits that use 
> switches/muxes,etc to allow you to page through settings with a switch or a 
> momentary button, i would be very happy to see other applications