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Validate

Walk the full pin map and confirm USB still works. Do not expect the display to light or the SHT40 to report values here — that comes after you flash.

Before you start

Checkpoint 4 passed. Everything from the earlier steps stays wired.

Schematic wiring: ESP32-S3 to SHT40 over I2C and ST7789 240×240 over SPI

The full map

ESP32-S3 SHT40 Display (ST7789)
3V3 VIN / VCC / VN VCC
GND GND GND
GPIO8 SDA
GPIO18 SCL
GPIO11 SDA (MOSI)
GPIO12 SCL / SCK
GPIO10 CS
GPIO9 DC
GPIO7 RST
GPIO21 BL

Rules

  • 3V3 only for sensor and display logic.
  • Do not join TFT SDA to SHT40 SDA.
  • Avoid GPIO 0 / 19 / 20 / 45 / 46 (and 35–37 on octal PSRAM) for new wires — BOOT already uses GPIO0.
  • S3 underside silk is mirrored vs top — match by label.

Check

Check What to look for
Walk the map Every row above has a jumper on the matching pin label
Two separate buses SHT40 uses GPIO8 and 18. Display SDA/SCL use GPIO11 and 12 and never share a wire with them
3V3 only No sensor or display pin is on 5V or VIN
Cool After a few seconds on COM, lightly touch the SHT40 and the display. If anything is warm, unplug and recheck power and ground
USB Data cable in the COM socket. Run the commands below 
lsusb | grep -iE '1a86|QinHeng'
ls -l /dev/ttyACM0 /dev/ttyUSB0 2>/dev/null

Bus 001 Device 015: ID 1a86:55d3 QinHeng Electronics USB Single Serial
crw-rw-rw- 1 root dialout 166, 0 Nov 10 22:12 /dev/ttyACM0

Expect the QinHeng serial bridge (1a86) and a port such as /dev/ttyACM0. The panel may stay dark. I2C at 0x44, backlight, and the setup QR are checked on Flash.

If it fails

Symptom Likely fix
No serial port Use a data cable in the COM socket (not native USB). USB group setup is in Flash
Something warm Unplug. Start at 3V3 and GND, then the last wires you added
The map doesn't match One jumper is on the wrong pin. Walk the table row by row

Checkpoint 5

  • The full map matches the table above
  • The I2C and SPI buses are not crossed
  • The board shows up on USB (lsusb and a serial device)
  • The SHT40 and display stay cool

Stop here until every box is ticked.

Next: Flash the ESP32