Digital Piano

Techno Keith

Hello,
I am making sort of a custom digital piano.· It will have over 100 different buttons which will each play a different note.· Should each button have a different resistor attached, and the propeller measuring the resistance to tell which button is being pressed?· How should I do this?

- keith

Mike Green

That's hard to do with so many buttons. That technique works best with fewer buttons. You're better off using scanning with maybe an 8 x 16 matrix using either 8-bit shift registers like 74HC595 for output and 74HC165 for input or maybe I2C I/O Expanders like the PCA9554. You probably want a diode at each button so you can detect multiple button presses.

If you have 24 I/O pins available, you can use those directly for scanning the buttons rather than using shift registers (8 + 16 = 24). It all depends on what you want to do overall.

Rayman

I think you only need 20 pins for a 10x10 input matrix, right?· I think this might give faster input than i2c, but maybe they're both fast enough for human input...

Techno Keith

What if I wired the buttons up to a keyboard?

Mike Green

What do you mean by "wired the buttons up to a keyboard"? Why would you do that?

Ariba

These Piano-Keyboards with black and white "keys" have normally 3 states per key, not only an On/Off switch. You have one contact for released keys, and one for a full pressed key, and in between neither of the 2 contacts is closed. This allows measuring the time between the begin of a keypress until the key is ful pressed. And that time you use for playing the notes dynamically louder and softer. Without that, a keyboard is nearly useless for playing Piano (there are other sounds like organ, which does'nt require a dynamical keyboard).
You also have to detect several concurrently pressed keys for a polyphonic playing, and all with individual measuered press times.

So you need some kind of analog multiplexer, with a 3 level detector at the end, and the Prop have to scan one key after the other, store the current state of the key and increment a counter for every key, if the key is between released an pressed state.

Andy