pimoroni SEN6x Breakout for Sensirion SEN66 - STEMMA QT / Qwiic

AI context

Dense context for pasting into a model prompt — addresses, pinout, voltages, tolerances and the vendor's reference circuit.

BOARD: Adafruit 6331, a 25.6 x 17.8 x 5.9 mm (2.0 g) adapter that lets a Sensirion SEN6x environmental sensor node plug into a STEMMA QT / Qwiic I2C chain. A 6-pin JST GH-compatible connector sits at the top edge for the sensor, two 4-pin JST SH QT connectors carry the host bus, and a 3.3 V regulator plus a two-channel BSS138 level shifter sit in between. The sensor and the GH cable are both sold separately and neither is in the box. Resold by Pimoroni; the maker is Adafruit.
ADDRESSES: the SEN6x sensors answer at 0x6B by default; the exception the vendor states is the SEN60, whose default is 0x6C. Nothing else on the board answers on the bus - the regulator and the level shifter are not I2C devices - so a scan on a bare board finds nothing.
PINOUT: 19 pads across four connectors, each numbered from 1 by the vendor, so three are offset and the offsets are stated here. Sensor connector X1 (JST GH 6-pin, SM06B-GHS-TB): 1 = 3V3, 2 = GND, 3 = SDA, 4 = SCL, 5 = GND, 6 = 3V3 - the sensor is fed 3.3 V on two pins and grounded on two, with SDA/SCL on the 3.3 V side of the shifter. Two QT connectors, JST_SH4, in parallel on the same nets: CONN1 pads 7-10 and CONN2 pads 11-14, each GND, VCC, SDA, SCL in that order. Spare unpopulated 5-hole 2.54 mm header JP1, pads 15-19: VCC, 3.3V, GND, SCL, SDA.
SUPPLY: VIN takes the same voltage as the microcontroller's logic - 3.3 V or 5 V - and feeds an AP2127K-3.3 LDO (U2) with a 10 uF input capacitor (C8); the 3.3 V output has a 10 uF (C9) and a 0.1 uF (C10) across it. The learn guide states 3Vo can supply up to 100 mA to external circuitry, and that is the rail the sensor connector hands the SEN6x.
LOGIC LEVEL: the QT side is level shifted, so the board takes 3-5 V logic on SDA/SCL; the sensor side is 3.3 V regardless. Q2 (BSS138 dual) is the shifter, one channel per line, and R1 is a 4-element 10K pack - two elements pull SDA and SCL up to VCC on the host side and two pull them up to 3.3 V on the sensor side, so both sides of the shifter have their own 10K pull-up.
REFERENCE CIRCUIT: everything is fitted - regulator, both 10K pull-up pairs, the BSS138 shifter, 10 uF in and 10 uF plus 0.1 uF out, and a green power LED (D2) with solder jumper SJ2 to cut it. The user supplies exactly two things: a 6-pin JST GH cable and the SEN6x sensor.
TRAPS: the board ships with neither the sensor nor the GH cable, and the GH connector is the only path to the sensor - a QT cable will not reach it. CONN1 and CONN2 are the same four nets in parallel, not a second isolated bus, so both ends of a chain see every device. The sensor is powered from the regulator's 3.3 V, so its supply current comes out of the same 100 mA the 3Vo pin advertises. JP1 is an unpopulated 5-hole header on the same rails, useful for probing but not a separate port. The address is the sensor's, not the board's: two SEN6x sensors on one bus collide unless one is reconfigured.