Unit I - ESP32 Advanced

49. Over-the-Air Updates

Ship a field-updatable node: first USB flash enables OTA, then change the firmware version banner and blink over Wi-Fi.

Estimated time 3 hours

Learning outcomes

Explain why sealed devices need OTA
Contrast ArduinoOTA with HTTP image pull
Keep ArduinoOTA.handle() responsive with millis timing
USB-flash once, then OTA-upload a visible behaviour change
Apply hostname and password safety habits

Parts and preparation

ESP32 DevKit on the same LAN as your PC, USB for first flash, LED on GPIO 2, WiFi credentials.

Before power: inspect wiring, confirm supply voltage and ensure all connected circuits share GND.

Libraries for this lesson

In Arduino IDE 2 open Tools → Manage Libraries…. Search by the Library Manager name and install the package by the exact author below. Similar names from other authors can use different APIs and will break the example.

Include	Library Manager name	Author	Install note
`WiFi.h`	WiFi	Espressif	Built into the esp32 Arduino core.
`ArduinoOTA.h`	ArduinoOTA	Espressif / Arduino	Built into the esp32 Arduino core.

Over-the-Air Updates instructional connection diagram

Project: Field-updatable node

Imagine the board is already installed in a ceiling box. You need to change behaviour without climbing a ladder for USB.

Sketch 1 (VERSION 1.0) enables OTA with a slow blink and a Serial banner. Sketch 2 (VERSION 1.1) is the update you push over the network port: faster blink and new banner. USB-upload sketch 1 first; OTA-upload sketch 2 to prove the field path.

PC Arduino IDE OTA upload over WiFi to ESP32 — USB once to enable OTA; later updates over Wi-Fi.

ArduinoOTA versus HTTP OTA

ArduinoOTA: IDE pushes over the LAN - perfect for labs. HTTP OTA: device pulls an image URL - typical for fleets. This lesson is ArduinoOTA end to end.

Style	Who starts	Use
ArduinoOTA	Developer PC	Lab / local
HTTP OTA	Device pull	Field fleets

BasicOTA flow and handle()

Flash with OTA code over USB -> board joins WiFi -> Tools Port shows network hostname -> upload again. loop must call ArduinoOTA.handle() often. Use millis for blinking - never long delay() that starves handle().

Safety notes

Unique hostname per board on busy lab WiFi. setPassword outside trusted LANs. Keep a USB cable for recovery if an update fails mid-way.

Wiring and safe build sequence

First flash: USB data cable
GPIO 2 LED shows version behaviour
PC and ESP32 on same WiFi

Power rule: switch off before moving wires. Arduino I/O pins are control signals; high-current loads require a driver and suitable external supply.

Worked sketch 1: Field node VERSION 1.0 (USB first)

Download .ino sketch

What this sketch is for: Install the OTA service once over USB. Slow blink and banner VERSION 1.0 prove this build is running. handle() stays responsive because blinking uses millis.

#include <WiFi.h>
#include <ArduinoOTA.h>

const char* ssid = "YOUR_WIFI_SSID";
const char* password = "YOUR_WIFI_PASSWORD";
const char* version = "1.0";
const int ledPin = 2;
const unsigned long blinkMs = 800;
unsigned long lastToggle = 0;
bool ledOn = false;

void setup() {
  Serial.begin(115200);
  pinMode(ledPin, OUTPUT);

  WiFi.mode(WIFI_STA);
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println();
  Serial.print("IP ");
  Serial.println(WiFi.localIP());

  ArduinoOTA.setHostname("wilteq-esp32");
  // ArduinoOTA.setPassword("lab-password");

  ArduinoOTA.onStart([]() { Serial.println("OTA start"); });
  ArduinoOTA.onEnd([]() { Serial.println("\nOTA end"); });
  ArduinoOTA.onError([](ota_error_t error) {
    Serial.printf("OTA error %u\n", error);
  });
  ArduinoOTA.begin();

  Serial.print("Field node VERSION ");
  Serial.println(version);
  Serial.println("OTA ready - network port wilteq-esp32");
}

void loop() {
  ArduinoOTA.handle();

  if (millis() - lastToggle >= blinkMs) {
    lastToggle = millis();
    ledOn = !ledOn;
    digitalWrite(ledPin, ledOn ? HIGH : LOW);
  }
}

How the code works

millis blink never blocks ArduinoOTA.handle().
Hostname wilteq-esp32 must be unique on a shared lab SSID - change it if needed.
Uncomment setPassword outside a closed classroom LAN.

Worked sketch 2: Field node VERSION 1.1 (OTA this one)

Download .ino sketch

What this sketch is for: After sketch 1 is running, select the network port and upload THIS sketch over OTA. Success: Serial shows VERSION 1.1 and the LED blinks faster - no USB required for the update. Match the breadboard layout below before upload.

Breadboard layout for ESP32 OTA field node: LED with series resistor on GPIO 2 — Breadboard for sketch 2: version-indicator LED with series resistor on GPIO 2 to GND. Same wiring as sketch 1. Click to enlarge.

#include <WiFi.h>
#include <ArduinoOTA.h>

const char* ssid = "YOUR_WIFI_SSID";
const char* password = "YOUR_WIFI_PASSWORD";
const char* version = "1.1";
const int ledPin = 2;
const unsigned long blinkMs = 150;
unsigned long lastToggle = 0;
bool ledOn = false;

void setup() {
  Serial.begin(115200);
  pinMode(ledPin, OUTPUT);

  WiFi.mode(WIFI_STA);
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println();
  Serial.println(WiFi.localIP());

  ArduinoOTA.setHostname("wilteq-esp32");
  // ArduinoOTA.setPassword("lab-password");
  ArduinoOTA.onStart([]() { Serial.println("OTA start"); });
  ArduinoOTA.onEnd([]() { Serial.println("\nOTA end"); });
  ArduinoOTA.begin();

  Serial.print("Field node VERSION ");
  Serial.println(version);
  Serial.println("OTA ready");
}

void loop() {
  ArduinoOTA.handle();
  if (millis() - lastToggle >= blinkMs) {
    lastToggle = millis();
    ledOn = !ledOn;
    digitalWrite(ledPin, ledOn ? HIGH : LOW);
  }
}

How the code works

Only version string and blinkMs changed - enough to prove the new image.
If OTA fails, recover with USB and sketch 1.
Same hostname and WiFi credentials as sketch 1.
Build from the breadboard photo: indicator LED on GPIO 2.

Test and record evidence

Expected result: After USB sketch 1: Serial shows VERSION 1.0 and a slow blink; network port appears. After OTA sketch 2: VERSION 1.1 banner and a clearly faster blink without reconnecting USB for the upload.

Practical evidence checklist

Labelled wiring or block diagram Uploaded sketch and observed result At least one measured/tested value Fault or improvement recorded in logbook

Common faults and checks

No network port: same LAN, firewall/mDNS, unique hostname, reboot IDE.
OTA stalls: confirm handle() runs; avoid delay-based blink.
Failed mid-update: USB recover with sketch 1.

Extension challenge: Enable setPassword, OTA again, and add a short onProgress Serial percent print.

Check your understanding

Q1. What field problem does OTA solve?

Show answer

Updating firmware without physical USB access.

Q2. Which call must run often?

Show answer

ArduinoOTA.handle().

Q3. Why avoid delay() for the blink here?

Show answer

Long delays starve handle() and can miss OTA.

Q4. How do you prove sketch 2 arrived?

Show answer

VERSION 1.1 banner and faster blink after network upload.

Q5. ArduinoOTA vs HTTP OTA?

Show answer

IDE push on LAN vs device pulls an image URL.

Q6. Why a unique hostname?

Show answer

Avoid flashing someone else's board on a shared WiFi.

Q7. Why keep USB around while learning?

Show answer

Recovery if an OTA image fails.

Q8. First enable step?

Show answer

USB-upload a sketch that connects WiFi and begins ArduinoOTA.