tldr wrote:how many more than 128 i/o pins do you need?
you could use one mcp23017 to set the address pins on a bunch of others on the fly. pretty sure it could work, but i'm having a little trouble wrapping my head around it at the moment. oops. i don't know if the chip checks its address once at power up or if it continually checks its address pins. probably in the data sheet. i'll check after dinner.
one thing, though. if you need a lot of switch inputs, the controller that adafruit uses for 8x8 matrices and 7 segment arrays is capable of scanning a 3x11 array of switches. i've got one on order to play with this weekend.
tldr wrote:different devices will use different address, but the address space is small, (7 bits, 128 unique addresses), so i would guess that each manufacturer tries to avoid conflicts between their own devices.
the led matrix backpacks i mentioned before have a base address of 0x70. mostly just the luck of the draw, i guess.
Which IC is used in those backpacks?
adafruit_support wrote:Which IC is used in those backpacks?
It is the HT16K33.
http://learn.adafruit.com/adafruit-led- ... 2c-address