Cheatsheet: ESP32 BLE Gadget: Build a Two-Way Phone Device

One-page lookup card for the whole course: board basics, toolchain, BLE two-way communication, and hardening.

Module 1: Set Up and Flash Your First Sketch

1.1 Meet the ESP32 Dev Board

Three meanings of "ESP32"

Term	Meaning
Chip	The bare Espressif SoC (e.g. ESP32-D0WD)
Module	Chip + flash + antenna (e.g. ESP32-WROOM-32)
Dev board	Module + USB, regulator, buttons (e.g. DevKitC)

Board parts and pin safety

Item	What to know
Logic level	3.3 V only. Never feed 5 V into a GPIO
Power	USB (5 V) or 3.3 V pin; board regulator handles the rest
Safe GPIOs	Most general pins; check your board's pinout
Avoid	GPIO 6 to 11 (wired to internal flash)
Strapping pins	GPIO 0, 2, 12, 15 affect boot mode; use with care
Input-only	GPIO 34 to 39 (no output, no pull-up)
Boot / Reset	Hold BOOT, tap EN to enter flash mode if upload stalls

[!WARNING] 5 V on a 3.3 V GPIO destroys the pin or the chip. Double-check wiring before powering.

1.2 Install PlatformIO and Flash a Blink Sketch

Install chain

1. Install VS Code.
2. Install the PlatformIO IDE extension.
3. Open PlatformIO Home, then New Project.
4. Name the project, pick your board (e.g. `Espressif ESP32 Dev Module`), pick the Arduino framework.
5. Write code in `src/main.cpp`, then Build and Upload.

Project layout

my-gadget/
  platformio.ini
  src/
    main.cpp
  lib/
  test/

platformio.ini essentials

[env:esp32dev]
platform = espressif32
board = esp32dev
framework = arduino
monitor_speed = 115200

Blink sketch

#include <Arduino.h>

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
  digitalWrite(LED_BUILTIN, HIGH);
  delay(500);
  digitalWrite(LED_BUILTIN, LOW);
  delay(500);
}

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