SCD40 — i2c address & wiring
True CO2 sensor using photoacoustic sensing.
Key facts
SCD40 at a glance
| i2c address | 0x62 fixed address |
|---|---|
| Logic voltage | 3.3–5 V |
| Type | sensor |
| Part | Sensirion SCD40 |
| Ships with | Qwiic, STEMMA QT |
| Datasheet | Sensirion SCD40 — manufacturer documentation ↗ |
The chip
What the Sensirion SCD40 actually is
Photoacoustic NDIR carbon dioxide (CO₂) sensor providing calibrated measurements of CO₂ concentration, temperature and relative humidity. Features automatic self-calibration, low power consumption and long-term stability for indoor air quality monitoring and ventilation control.
Wiring
How to connect the SCD40
The SCD40 talks i2c at address 0x62. It runs at 3.3–5 V, so match your host's logic level — if your host is 5 V and a board on the bus is 3.3 V-only, add a level shifter. Use the compatibility checker to confirm the exact cable for your setup.
The address is fixed, so two SCD40s can't share a bus directly — the address-conflict guide covers the workarounds (multiplexer, second bus).
Wiring is the usual four: power, ground, SDA and SCL, plus pull-up resistors — almost always already fitted on the breakout. Nothing showing up? Run an i2c scan first; if the bus is silent, the 7-step checklist finds it faster than guessing.
Ecosystems
Plug-together options for the SCD40
SCD40 breakouts ship with Qwiic and STEMMA QT — keyed 4-pin cables carrying power, ground, SDA and SCL, so there's nothing to solder and nothing to wire backwards. Chain it to the next board and keep going.
Running a mixed bench? Those ecosystems interoperate more than their marketing suggests — see every connector pairing for the cable or adapter you need, or the standards overview for how they compare.
Go deeper
Guides covering the SCD40
Alternatives
Other air quality boards
Get one
Questions
SCD40 i2c FAQ
What is the SCD40's i2c address?
The SCD40 sits at a fixed address of 0x62. It can't be changed, so two of them can't share one bus without a multiplexer or a second bus.
What voltage does the SCD40 run at?
3.3–5 V logic. That range covers both 3.3 V and 5 V hosts, so it drops onto a Pi, ESP32 or Arduino without a level shifter.
Can I use two SCD40s on one i2c bus?
Not directly — every SCD40 answers to 0x62, so two on one bus would collide. Use a TCA9548A multiplexer to give each its own channel, or put the second one on a separate bus.
Does the SCD40 work with Qwiic and STEMMA QT?
Yes — SCD40 breakouts ship with Qwiic / STEMMA QT, so it plugs straight in with no soldering. Mixing ecosystems? The compatibility checker gives you the exact cable or adapter.