STEMMA QT i2c connector
Adafruit's JST-SH system, connector-identical to Qwiic. On-board level shifting means 3.3 V or 5 V.
Pinout
STEMMA QT pinout
STEMMA QT runs a 4-pin JST-SH at 1 mm pitch, wired GND → V+ → SDA → SCL looking into the socket. The pin order is the part that actually matters: a connector that physically fits but is wired differently will land SDA where SCL should be, and the bus simply goes quiet. Because Qwiic use the same connector and the same order, their cables cross over with nothing in between.
Specs
STEMMA QT at a glance
| Vendor | Adafruit |
|---|---|
| Connector | JST-SH |
| Pins | 4 |
| Pitch | 1 mm |
| Logic voltage | 3.3 V or 5 V |
| Chainable | yes |
| Interrupt pin | no |
| Official docs | Adafruit's STEMMA QT documentation ↗ |
Watch out: Qwiic devices won't tolerate a 5 V STEMMA QT host — add a level shifter for that combo.
Voltage & chaining
Living with STEMMA QT on a real bus
STEMMA QT is 3.3 V or 5 V. The connector tolerates both rails — but the boards hanging off it may not, so check each part's own range rather than trusting the ecosystem. The level-shifting guide covers the mixed-rail case.
Chaining is the point of STEMMA QT: two connectors per board, so you hop from one to the next and they all share SDA and SCL. Two things end the party — two boards answering the same address (see address conflicts for the fixes), and the pull-ups. Every board adds its own pull-up resistors in parallel with the rest, so a long chain drives the combined resistance down toward the point where the bus can't pull low cleanly.
Cable length is the other quiet limit — i2c budgets 400 pF of total bus capacitance, and every extra centimetre spends it. Inside an enclosure you'll never notice; if you're reaching across a room, read how far i2c actually goes first. If a chain stops responding, an i2c scan tells you whether it's a wiring or an addressing problem.
Compatibility
Connecting STEMMA QT to other standards
Every pairing below is pre-answered — whether it's a direct cable, an adapter, or a level shifter first. Or skip to the compatibility checker and pick both ends.
Boards
Boards that ship with STEMMA QT
22 boards in our dataset ship with STEMMA QT — plug-together, no soldering. Each page lists its i2c address, voltage range and wiring notes.
Questions
STEMMA QT FAQ
What connector does STEMMA QT use?
A 4-pin JST-SH at 1 mm pitch, wired GND / V+ / SDA / SCL. That's the same physical connector and pin order as Qwiic, so cables interchange directly.
What voltage does STEMMA QT run at?
3.3 V or 5 V. That tolerance is why it survives mixed benches, but the boards on the chain may not be — check each board's own range before mixing.
Can you daisy-chain STEMMA QT?
Yes — STEMMA QT boards carry two connectors, so you chain one to the next and every device shares the same SDA/SCL. Two limits bite eventually: each board must have a unique address, and every board adds pull-up resistors in parallel plus cable capacitance.
Does STEMMA QT have an interrupt pin?
No. STEMMA QT carries only power, ground, SDA and SCL. A sensor with an interrupt output needs that pin wired separately to a spare GPIO — i2c itself has no way to signal "data ready" on the bus.
What should I watch out for with STEMMA QT?
Qwiic devices won't tolerate a 5 V STEMMA QT host — add a level shifter for that combo.