Phase 4 — Wire I2C + scan¶

Add SDA / SCL and confirm SHT40 and BMP390 answer on the bus. Power from Phases 2–3 stays on.

Firmware¶

Changed. New folder firmware/04-i2c-scan/. Do not edit 01-hello. Pins SDA=8 SCL=18.

Preconditions¶

Checkpoint 3 passed
Sensor VCC/GND already on the 3V3 star
Unplug USB while seating the two data jumpers

4.1 Data wires¶

S3	SHT40	BMP390 (I2C silk)
GPIO8	SDA	SDI (sometimes labeled SDA)
GPIO18	SCL	SCK

BMP390 breakouts usually don’t print SCL/SDA — they reuse SPI names. For I2C: SCK = clock, SDI = data. Leave BMP390 CS and SDO open (Adafruit pinouts).

Both wires or nothing — one alone → found none. Do not wire TFT SPI yet.

4.2 Flash scanner¶

Stop any serial monitor on COM first.

cd firmware/04-i2c-scan
pio run -e esp32-s3-n16r8 -t upload --upload-port /dev/ttyACM0

Connected to ESP32-S3 on /dev/ttyACM0:
…
Hash of data verified.
Hard resetting via RTS pin...
========================= [SUCCESS] Took 13.70 seconds =========================

pio device monitor -b 115200 --port /dev/ttyACM0

weather i2c-scan — phase 4
SDA=GPIO8 SCL=GPIO18 expect=SHT40~0x44 BMP390~0x76/0x77
--- i2c scan ---
found 0x44
found 0x77
devices=2

Expect 0x44 (SHT40) and 0x76 or 0x77 (BMP390) every scan. This bench: 0x44 + 0x77, stable. Note any other addresses as ghosts.

4.3 If no device¶

Confirm both data wires seated on each module (BMP390: SDI+SCK, not CS/SDO)
Recheck data/clock not swapped
Shared GND confirmed on the star
Shorter jumpers; power still ~3.3 V on each VCC

Checkpoint 4¶

[x] Serial scan lists SHT40 (~0x44) and BMP390 (~0x76/0x77)
[x] Addresses stable across resets
[x] Logged in lab-log.md

Stop here until checkpoint passes.

Next: Phase 5 — Climate read