Unpowered inspection practice

Inspect the sensor wiring

Practice tracing one documented route: the original Pico RP2040 to the Adafruit BME280 STEMMA QT breakout’s pad row. This is a visual netlist exercise—not a simulator, arbitrary-circuit checker, or hardware qualification.

Look first

Trace the displayed endpoints

Wiring case

A simplified endpoint netlist, not a physical placement or orientation drawing. Read the printed labels and use the manufacturer pinouts before touching a board; wire colors are not evidence. On a narrow screen, scroll the diagram sideways or use the connection table below.

Connections visible in this case
Pico source	BME280 destination
Physical 1 · GP0	SDI / SDA
Physical 2 · GP1	SCK / SCL
Physical 36 · 3V3(OUT)	VIN
Physical 38 · GND	GND

Reference wiring

Open this when you want a side-by-side check. These four connections are the complete reference for this exercise:

Physical 1 · GP0 → SDI / SDA
Physical 2 · GP1 → SCK / SCL
Physical 36 · 3V3(OUT) → VIN
Physical 38 · GND → GND

SDI means SDA here, and SCK means SCL. Sensor VIN is the input used in this route; the sensor’s 3Vo pad is a regulator output and is not connected.

Decide safely

Name the mapping and the next check

Your diagnosis

The four reference connections matchSDA and SCL are exchangedThe ground connection is missingA GPIO is being used as the power connection

Unpowered check

Disconnect USB/external power, then trace all four reference pathsDisconnect USB/external power, then trace SDA and SCL by labelDisconnect USB/external power, then continuity-check the ground pathDisconnect USB/external power, then trace 3V3(OUT) to VINWrong method: power it and see whether the sensor responds

Breadboard mini-check

One row, two isolated strips

On this generic example, a–e in row 10 share one five-contact strip. The center trench separates f–j, and row 11 is a different strip. Power rails are not shown.

Which contact shares a strip with a10?

e10f10a11

Use the labels, then verify

Manufacturer pin references

Original Pico R3 numbered pinout (PDF)Adafruit BME280 power and signal pinouts

This visual check cannot prove solder-joint quality, contact resistance, supply health, sensor calibration, or compatibility with a project whose wiring or firmware has been modified. The project’s own files remain authoritative for a modified build.