And the next disappointing revelation.
@FiDel, you were right after all. The TTP229-L does support I2C, but the chip on the keypad is a TTP229-B which doesn’t.
So we have to use the other approach, but that’s not too bad after the insight that the main advantage of having multiple pads on one I2C bus is not an option due to the inability to select other addresses for the keypad.
I’ll keep you posted.
BTW, these should be the correct datasheets
https://dl.dropboxusercontent.com/u/87066238/SUNROM-TTP229-BSF_V1.1_EN.pdf
http://www.sunrom.com/get/611100
https://dl.dropboxusercontent.com/u/87066238/TTP229B-Schematic.pdf
https://www.openimpulse.com/blog/wp-content/uploads/wpsc/downloadables/TTP229B-Schematic-Diagram.pdf
this explicitly states " with 2 wire SPI type data interface (not I2C)"
http://www.sunrom.com/p/ttp229-bsf-8229bsf-ssop28-spi
http://www.sunrom.com/p/816-channel-capacitive-touch-module-ttp229