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Free public beta until December 4, 2026: every course is open, no card needed. After that, the first chapter of each course stays free and full access is a one-time $39 ($19 for up to 100 founding members chosen for helpful feedback). Your progress is kept. How the beta works

Recipe

Upload firmware to a board

Use when: you have a sketch that compiles and a board on a USB cable, and want the board running it

Goal: the board running the new program, confirmed by what it does

Taught in Bootloaders and uploading

Quick recipe

  1. Select the board
  2. Select the port
  3. Compile
  4. Upload
  5. If it can't connect, force upload mode by hand
  6. Confirm it runs
  1. 1

    In the IDE pick the exact board (ESP32S3 Dev Module, Arduino UNO R4 Minima); with arduino-cli use its FQBN.

    Why: the board decides the compiler, the addresses and the upload tool.

  2. 2

    Choose the port that appears when you plug the board in.

    • no port — check the cable, then force upload mode (step 5).
    • two new ports (a DevKitC-1 plugged in by both connectors) — pick the one for the connector you mean to use.

    Why: the upload tool sends to exactly one port.

  3. 3

    Click Verify, or run arduino-cli compile --fqbn <fqbn> <sketch>. Fix the first error before anything else.

    Why: an upload can only send a build that exists.

  4. 4

    Click Upload, or run arduino-cli upload -p <port> --fqbn <fqbn> <sketch>. Wait for the tool's "done" message.

    Why: the tool restarts the board into its bootloader, sends the image and restarts it again.

  5. 5

    ESP32-S3: hold Boot, press and release Reset, release Boot, then upload. Uno R4: double-tap Reset right after plugging in, then upload (the port name may change; select it again).

    Why: a crashed sketch can't answer the tool's request to restart, but the bootloader always can.

  6. 6

    Watch the board do what the sketch says. If it waited in download mode, press Reset once to start the new program.

    Why: "upload complete" proves the bytes arrived, not that the program behaves.

Common mistakes

  • Uploading with the wrong board selected: it compiles for the wrong chip.
  • Keeping a serial monitor open in another program, which holds the port.
  • Wiring a strapping pin so it is pulled low at reset, which sends the ESP32-S3 into download mode every time.