by crochambeau » Thu Jun 24, 2021 1:31 pm
Since my earlier post did not scare you off, I will go a little deeper..
Playing with CMOS switching was a mind opening experience for me. I'm happy to throw in possible solutions/angle to specific problems, but you'll need a roadmap first.
My method (and please bear in mind that there are probably more efficient ways to go about this that I do not know about) would be to label the circuit nodes and pot legs with separate letters or numbers, and then write out all of the intended connections. So say you have a pot and designate that A, B, and C, and then each circuit node has a number running from 1 to 7. You'd wind up with a (partial) map looking like this:
A1, B1, C2
A3, B3, C4
A5, B6, C7
Where each column is a pot lug, and each row is a circuit node.
This way you can map out everything that needs to happen from any vantage point. Example: lug A needs to connect to 1, 3, and 5. I'd probably steer toward a 4052 for this, but it can be done with simpler switches (mental horsepower will usually need to increase in the design phase to use simpler parts).
Repeat until all needed switch modes are addressed, and then we look at the logic needs of the switches to achieve that.
So say we determine that a 4052 needs a 01 in order to meet the needs of a given state, and in this state the switch position is in 11. You can strap a NAND gate across your two bit data line, that will output a low state when both inputs are high, and connect that to the instruction pin (so long as that pin needs a high signal during the other two configurations).
Dig into the truth tables for AND, OR, NAND, and NOR for other ideas. Sometimes you need to combine a couple layers of "instruction" (even though this is hardware, it's essentially low level programming) to get your needs met.