Originally Posted by gipetto
the tindie board was built to handle 3.3v and 5v. I'm not sure that would be possible using resistors. you could get away with even few level converters by changing the design to 3.3v mcu but that could make side buttons more susceptible to double click.
The 3.3v/5v to 1.9v is handled by the voltage regulator chip, then the level converters use the 1.9v from that to change the SPI voltage to 1.9v.
I think I might have figured out why they are needed now.
Basically VDDIO on the sensor is set to 1.9v from the voltage regulator, and so the SPI voltage should match the VDDIO, so the level converters are used to set the SPI signals from the MCU to 1.9v, to match the VDDIO voltage.
The VDDIO has a maximum voltage of 3.6v, so it can't be set to 5v, and the only other option is 1.9v, unless another voltage regulator is used, so might as well use the same 1.9v.
So I am assuming that VDDIO's voltage is meant to match the SPI voltage (I guess so it can interpret the signals properly?), if that's the case then you can't use 5v SPI signals, so I'd have to keep the level converters.