Making analog presets with CMOS

[Processaurus]

Here was an interesting question Nordine from Chile asked me today, I thought I would repeat the question here, and see if anyone else had implemented or had thoughts on using a bunch of trimpots in a pedal that are selected electronically to make "presets" of favorite settings you want to reproduce reliably and quickly:

Right now im trying to find a way to generate presets using CMOS, and im a bit confused. While looking at posts, i found yours:

"An analog version that's been suggested here would be to use a bunch of trim pots for the different "presets", and select them with CMOS 4052's (DP4T) or 4051's (SP8T).  That approach would be much easier for a smaller number of presets, but would start getting to be too many parts if you wanted a bunch of presets.  But most pedals don't really have an infinite number of useful, distinct sounds.  I like about 4 on the fuzz factory."

Would you please expand a bit on HOW would a 4052 or 4051 (or 4053)would serve as preset switching devices?

What im after: id like to make 3 presets (for 2 presets i can do it with a 3PDT stompswitch), so, i'd have 2 knobs (we'll call them depth and speed) triplicated (6 knobs) and i'd like to switch between these pairs with a momentary stompswitch, so it goes on preset 1, 2 and 3.. and also, id like to have LEDs lightning up on each preset i set

Which CMOS chip would serve me better for this? And how? i know i can't ask for a complete tutorial on this issue, but if you could give me pointers, id do my homework  

Good question, it's just something I've just thought about... but think of the CMOS analog switches as logic controlled rotary switches.  You can control many many of the switches from a single logic signal, and do things like you would do with a giant, expensive, multi pole rotary switch like you see in those old computer monitor or printer switcher boxes.  I would use the CD4052 for switching pots, because you can use the two poles to simultaneously switch the pot wiper and one other pot lug into the circuit, and on all the trim pots leave their third lugs still connected (as it can't do anything electronic with just one end connected).  On the data sheet for the 4052 study the truth table, about which outputs are selected based on the state of the logic inputs.

To make the driving logic signal for the 4052, which uses 2 input pins to read a 2 bit binary number (for example switch throw 1 is active when the two logic inputs are 0,0; switch 2 is 0,1; switch 3 is 1,0; and switch 4 is 1,1) from a momentary switch, look at counter IC's that have a binary output.  There are a few, and they work by counting an clock input, and spitting out a binary representation of the count, on a few output pins.  Look at how the 40193 counter here is working to make the 4051 select it its 8 switch throws by using Qa, Qb, and Qc to send a binary number to the 4051 logic inputs, every time the CU pin (in count up mode, what you'd use) goes pulled low.  There's a lot of extra stuff there you don't need in the geofex circuit (like count down and random), but it shows that counter IC in action.


The 4052 only has 2 logic inputs, rather than the 4051's 3 logic inputs, but same idea.

Lastly, look at momentary switch debouncing for your physical switch you're using, you don't want your counter to stutter.

http://tech.thetonegod.com/debounce/debounce.html

Hope that helps, feel free to ask any more questions or show me a schematic you're working on.