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Engineer questions written as pages. An AI search can point at one URL instead of a whole catalog.

• ESP32 status LED does not blink. What should I check first? — Confirm the GPIO in firmware matches this board. GPIO2 is common on ESP32-DevKit; many C3 boards use GPIO8. Copying the pin from another chip is the usual miss.
• ESP32 joined Wi-Fi but never gets an IP. Where do I look? — Station mode needs a router that hands out DHCP. A phone hotspot that requires a captive portal will sit associated with no usable IP.
• Why is ESP32 deep-sleep current still high? — Deep sleep only helps if wake pins are not floating and peripherals are really off. A floating GPIO can leak milliamps.
• ESP32 MQTT client never stays connected. What usually breaks? — MQTT needs a working Station IP and a reachable broker. If DNS or the port is blocked, the client retries forever with little in the log.
• Phone cannot find the ESP32 BLE device. What is missing? — Advertising must be running, and the name/UUID the phone filters on must match. A GATT server that never advertises is invisible.
• How do I talk to a meter on RS-485 from ESP32 UART? — UART echo only proves TX/RX and baud. RS-485 is a transceiver and a DE/RE pin, not a different UART peripheral.
• ESP32 I2C scan finds nothing. What is usually wrong? — Pull-ups must exist on SDA and SCL (typical 2.2k–10k to 3.3V). Many breakout boards already have them; a bare chip does not.
• How do I wire a 2.0 inch ST7789 SPI TFT to ESP32? — ST7789 panels are usually 4-wire SPI plus DC, RST and backlight. Match the 12-pin FPC pinout on that exact module — pin numbers are not universal.
• ESP32 OTA fails after the first update. What should be on the board? — Native OTA needs two OTA partitions and a partition table decided on board one. A single factory partition cannot swap images.
• Where should ESP32 store SSID and calibration so they survive reboot? — NVS, not RAM and not a hardcoded string in firmware. SSID, keys, serial numbers and calibration belong in namespaces you control.
• Does ESP32 TWAI mean I can drop the board on a CAN bus? — TWAI is the controller on the chip. You still need a CAN transceiver, termination, and a common ground plan.
• How does a production ESP32 get its SSID without a USB cable? — Provisioning is a product flow: SoftAP, BLE, or a phone app. The Station example assumes the SSID is already in NVS or the code.

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