this is a complicated question!

:-? I am in the process of assembling a MIDI drum trigger for my computer. So far everything hardware wise is up and running but having only six analog inputs for my piezo triggers seems a little bit limiting. Can the piezo triggers be used to send a digital signal to give me 8 or more channels or am I stuck to using switches? I have a work around in mind to compensate for this but having a wire running to the drum stick to strike a metal contact pate seems a little self defeating especially if you get really wound up and start to shred and get tangled in wires. I also thought about the possibility of compensating by attempting to use “If/Then” logic in the programming so that if two analog channels receive a signal simultaneously to produce a different tone pulse to be sent to the computer but then that may defeat other pre-programmed sounds that might have to be made simultaneously during play.
Can programming be used to squeeze more potential sound channels from the 6 analog inputs using the simultaneous multiple inputs method (again if a signal is received by channel 2 and 3 to produce sound channel 7) or is it a pipe dream?
:-[Keep in mind I am no electronics engineer and I am no programmer by any stretch of the imagination. My strength is hardware. Heck, I put together and tested a Freeduino board I made and it worked. ;D
I am keeping in mind that multi signal reception may cause confusion and incorrect signaling to the compute so that is why I am asking those who may and do know more than me about programming whether or not this is a practical way of increasing output and input channels or if I have to add a signal expansion upgrade to the Freeduino board.
And to all of us Americans in this forum, HAPPY 4th of JULY!!! ;D ;D ;D

Since it is MIDI, you ought to be able to daisy chain duinos till you have enough piezos. I don't know about combining piezos into new channels, certainly possible if YOUR timing is good enough :)

Also if some piezos don't need an analog input (i.e. non-dynamic) then you can digital read those and save the analog pins for the dynamic piezos.

I have a cheesey kit like that, the pads are dynamic, but the foot pedals are binary.

Thanks for getting back so fast to this! I know this may seem fundamentally bonehead of me to ask this but how does one tell if a piezo is dynamic or not? I find this of particular interest because if I can use piezos on the digital channels as well that means I have a total of up to 16 possible inputs! (18 if channels 12 and 13 on the digital side of the board can be programmed as inputs!) That can lead to a very interesting percussion set! I have yet to fully wire my setup until I can figure out how to maximize the utility of what I got and having more than ten channels available to me adds new wrinkles on my project. I also have been contemplating designing a digital xylophone but I think on that project I may need three or four arduinos to make a full set. Being able to determine dynamic vs. non-dynamic piezos will help in the decision making part of the project. Now strangely I was wondering (because I do see a relation of how inputs work for this!) was how a keyboard on a computer with only four contacts with usb (nine pins in the classic connector and fourteen pins in the real OLD school computers.) can discern the difference between 101 to 130 DIFFERENT input signals from the keys. If I remember usb has +/- reference voltage and +/- signal voltage (all of it 5v). One of the pairs of contacts provide power for the device and the other two provide a + or - signal. Does it use voltage strength and variable resistance to provide a signal or does it use some kind of digital pulse? I know it is a side track question but one I have been wondering if the principle usb uses (or at least a keyboard) to open up more signal control potential through an arduino. :-?

how does one tell if a piezo is dynamic or not?

They will all make a dynamic signal. But you can hook it up to a digital read pin and the arduino will just register a one or a zero depending on how hard you hit it. This was in place of the drumsticks with wires on them :)

re: multiplexing switches, sure, if you had a bunch of footswitches on the digital pins you could control what midi voice/note the piezos will generate. Plenty of other possibilities too.