What's the best way to get LOTS (at least 48) of capacitive touch inputs?

I posted something that lead to this a while ago which you can read here if you'd like, where I ultimately decided that the MPR121 breakout board is my best bet, but now I'm focusing on... how the heck am I going to get at least 48 inputs from the 12 it provides? Here are some of my ideas:

1) Is multiplexing the electrodes possible? Like an example would be to attach 4 relays to each electrode, but obviously I don't want to do specifically that for several reasons... but yeah if I can multiplex them a different way that'd be great

2) Could I use multiple boards? Each board provides 12 electrodes, which, conveniently, is 48/4, so I could use 4 boards and do it that way (although that would be second choice due to software changes, hardware complications and ugliness, and expenses

3) I'm using this for a touch-sensitive piano keyboard, so would there be a way I could combine more than one key into an electrode and still get an accurate result due to the fact that the sensor is analog rather than digital? LOL could I just have the whole 32 keys be hooked to 2 electrodes??? That'd be awesome and hilarious, and the more I think about it, the more this sounds like my best option Nope, even if this worked, it would eliminate multitouch abilities. Never mind.

4) It occurs to me that quite some time ago I saw someone use a strip of metal as a range detector by sending an electrical impulse and measuring the time it took to get back kind of like sonar, but I can't seem to find the video anywhere and I've forgotten how he did it! But if this is an option, I might ditch the capacitive sensor altogether and do that...

Let me know if you have any experience doing these, have thoughts on how they might go, or have any other ideas for how to get this thing working; help is much appreciated! :)

It is good form, and makes it more likely you'll get an answer, if you provide links to the breakout board. Like this one?

https://www.sparkfun.com/products/9695

1) Is multiplexing the electrodes possible? Like an example would be to attach 4 relays to each electrode, but obviously I don't want to do specifically that for several reasons... but yeah if I can multiplex them a different way that'd be great

Probably not. A discontinuity in capacitance will look like a touch.

2) Could I use multiple boards? Each board provides 12 electrodes, which, conveniently, is 48/4, so I could use 4 boards and do it that way (although that would be second choice due to software changes, hardware complications and ugliness, and expenses

I think that would be my first choice.

3) I'm using this for a touch-sensitive piano keyboard, so would there be a way I could combine more than one key into an electrode and still get an accurate result due to the fact that the sensor is analog rather than digital? LOL could I just have the whole 32 keys be hooked to 2 electrodes??? That'd be awesome and hilarious, and the more I think about it, the more this sounds like my best option

I doubt it. This isn't like those methods of connecting a bunch of pushbuttons to one analog input with resistors so each keypress is a different analog value. Those buttons are on or off, whereas a capacitive touch sensor is a very analog thing.

4) It occurs to me that quite some time ago I saw someone use a strip of metal as a range detector by sending an electrical impulse and measuring the time it took to get back kind of like sonar, but I can't seem to find the video anywhere and I've forgotten how he did it! But if this is an option, I might ditch the capacitive sensor altogether and do that...

No, the way it works is to charge the capacitance of the strip of metal through a resistor. The time it takes to charge to some setpoint is a function of the resistor and the capacitance. You touch the metal, it increases the capacitance and therefore the time to charge.

Some eBay sellers have them as cheap as $2.50 USD each.

It is good form, and makes it more likely you’ll get an answer, if you provide links to the breakout board. Like this one?

https://www.sparkfun.com/products/9695

Noted… yeah that’s the link I was looking at; I’ll post it into my question. Thanks for the tip!

Probably not. A discontinuity in capacitance will look like a touch.

Yeah, I was worried about something like that happening… admittedly not that specifically, but you’re probably right. I’ll look at other options.

I think that would be my first choice

Although it isn’t mine, I think the multiple boards may be the best thing thus mentioned… Now I would just need to know HOW to do that. I can’t find anything like that that’s been done before; do you have any links that might help me out with that?

I doubt it. This isn’t like those methods of connecting a bunch of pushbuttons to one analog input with resistors so each keypress is a different analog value. Those buttons are on or off, whereas a capacitive touch sensor is a very analog thing.

I’m not sure I quite see your argument here; however, it doesn’t really matter now because I realized that doing this, even if it worked, I could play only two notes simultaneously at best which would defeat the whole purpose of this project.

Some eBay sellers have them as cheap as $2.50 USD each.

Yeah, I suppose I’m not really worried about pricing now that I’ve found some cheaper ones; I would just need to know how to deal with them once I have them.

However, I did think of one other thing: would there be a way I can put the electrodes in a matrix, kind of like how the inside of a computer keyboard works? Obviously I couldn’t do exactly that because those typically use multiplexed grounds and whatnot, but what if I put two electrodes on top of each other and had the Arduino check which two electrodes showed up as touched (giving me a total of 36 virtual electrodes from 1 12-electrode board)? My only fear here is that this might also eliminate multitouch abilities… thoughts? Yeah I drew this out and it will eliminate multitouch… never mind that then; it’s looking like my only option is to hook up 4 boards, which I still don’t know how to do.

Ok quick update on this: I found this forum thread of someone with a similar problem, and it focuses mainly on software. Within that thread is a link to this thread which focuses mainly on hardware. It could be that I'm just tired right now, but I don't fully understand what either of the posts are saying. It sounds like they got it to work, but can someone simplify it for me? It doesn't seem like it should be very complicated!