I believe the theory was that you’d power using USB and use the VIN pin on the Photon as a power output. It can source about 4.8 volts at 1A, well within the capabilities of the sensor (3.3V to 6V at < 130 mA). Since most of the IO pins are 5V tolerant in digital mode in INPUT mode (with no internal pull-ups or pull-downs) you should be all set with no level shifters or resistors. Or at least that how I would hook it up.
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