Connecting to a Network

Learning Goals 5 min

Yesterday you saw your local WiFi networks. Today you join one. By the end of this lesson you will:

1. Connect an ESP8266 / ESP32 to a known WiFi network using SSID + password from your sketch.
2. Read back useful information from the connection: assigned IP address, MAC, gateway, RSSI of the active link, channel.
3. Add reliable reconnection logic that survives transient drops (router reboot, signal blip, board reset) — the difference between a demo sketch and something you'd leave plugged in for weeks.

Warm-Up 10 min

Have ready: your ESP board, USB cable, your WiFi network's SSID and password. Best to use your phone's hotspot if your home/school network has heavy authentication (corporate WPA-Enterprise, captive portal).

Security note before we put a password in code

WiFi passwords in plain text inside a sketch are common in tutorials but not a great idea long-term:

• Anyone with access to your computer or GitHub repo can read it.
• If you share the sketch with classmates, your password goes with it.

For school work, use a throwaway password on your phone's hotspot rather than your main home password. For real deployments, configure WiFi via a captive portal (the user enters credentials in a browser the first time), or via a hardcoded but unique-per-device password. We'll discuss in L04.

New Concept · WiFi.begin and reconnection 25 min

The minimum viable connect

#if defined(ESP8266)
  #include <ESP8266WiFi.h>
#elif defined(ESP32)
  #include <WiFi.h>
#endif

const char* SSID     = "YourNetwork";
const char* PASSWORD = "YourPassword";

void setup() {
  Serial.begin(115200);
  delay(500);
  Serial.println();
  Serial.print("Connecting to "); Serial.println(SSID);

  WiFi.mode(WIFI_STA);
  WiFi.begin(SSID, PASSWORD);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  Serial.println();
  Serial.print("# Connected. IP = "); Serial.println(WiFi.localIP());
  Serial.print("# RSSI       = "); Serial.print(WiFi.RSSI()); Serial.println(" dBm");
}

void loop() { }

Three steps:

1. Mode: WIFI_STA = station / client.
2. Begin: hands SSID and password to the radio. Returns immediately; connection happens in the background.
3. Wait: poll WiFi.status() until it returns WL_CONNECTED.

What WiFi.status() returns

What the assigned IP tells you

• WiFi.localIP() — the IP address your router assigned via DHCP. Use this from a browser on the same network to reach the board.
• WiFi.gatewayIP() — your router's IP. Useful for diagnostics (ping it to confirm the route is alive).
• WiFi.subnetMask() — usually 255.255.255.0 for a home network. Tells you which IPs are "local".
• WiFi.macAddress() — your board's unique MAC. Useful if you want to give it a static IP reservation in your router.

Reconnection logic — production-ready

WiFi drops happen. Routers reboot. Signals fade. A polished sketch survives:

const unsigned long RECONNECT_EVERY_MS = 5000;
unsigned long lastReconnectAttempt = 0;

void ensureWiFi() {
  if (WiFi.status() == WL_CONNECTED) return;
  if (millis() - lastReconnectAttempt < RECONNECT_EVERY_MS) return;
  lastReconnectAttempt = millis();

  Serial.println("# WiFi lost; reconnecting...");
  WiFi.disconnect();
  WiFi.begin(SSID, PASSWORD);
}

void loop() {
  ensureWiFi();
  // ... your normal work here ...
}

ensureWiFi() is a non-blocking re-connector. Every 5 seconds while disconnected, it tries again. While connected, it returns instantly. Drop it at the top of loop() in every WiFi sketch you write.

Static IP (optional)

DHCP gives a random-ish IP each time. For a tiny webserver you want to bookmark, configure a static IP:

IPAddress staticIP(192, 168, 1, 42);
IPAddress gateway (192, 168, 1, 1);
IPAddress subnet  (255, 255, 255, 0);

WiFi.config(staticIP, gateway, subnet);
WiFi.begin(SSID, PASSWORD);

Call WiFi.config() before WiFi.begin(). Make sure the static IP is outside your router's DHCP pool to avoid collisions.

Worked Example · Connect + diagnose 25 min

Step 1 — fill in your credentials

Take the §3 sketch and replace YourNetwork / YourPassword with real values (phone hotspot is easiest).

Step 2 — upload at 115200 baud

You should see:

Connecting to Aisyah-iPhone
....
# Connected. IP = 172.20.10.3
# RSSI       = -55 dBm

Three dots = three half-second polls = ~1.5 s to connect, which is normal. Cold-boot connect can take up to 10 s on a busy network.

Step 3 — full diagnostic dump

Replace the lines after "Connected" with this:

Serial.print("# SSID       = "); Serial.println(WiFi.SSID());
Serial.print("# IP         = "); Serial.println(WiFi.localIP());
Serial.print("# Gateway    = "); Serial.println(WiFi.gatewayIP());
Serial.print("# Subnet     = "); Serial.println(WiFi.subnetMask());
Serial.print("# DNS        = "); Serial.println(WiFi.dnsIP());
Serial.print("# MAC        = "); Serial.println(WiFi.macAddress());
Serial.print("# RSSI       = "); Serial.print(WiFi.RSSI()); Serial.println(" dBm");
Serial.print("# Channel    = "); Serial.println(WiFi.channel());

This is your "network info" banner. Print it once at boot in every WiFi sketch — gives you all the diagnostic context you need when things go wrong.

Step 4 — ping the board from your laptop

On the same network, open a terminal and run ping 172.20.10.3 (replace with your board's IP). You should see replies every second. The board is now a real network device — your laptop can find it by IP.

Step 5 — test reconnection

Add the ensureWiFi() helper from §3 to loop(). Then while the sketch is running, briefly turn off your phone's hotspot. The board prints "# WiFi lost; reconnecting...". Re-enable the hotspot. The board reconnects automatically.

Step 6 — measure typical link quality at different distances

Put the ESP next to the router; note the RSSI (probably −30 dBm). Move 5 m through one wall; note again (probably −55 dBm). 10 m through two walls; probably −75 dBm. This is the data you need to plan where in your house a WiFi-powered project will actually work.

Try It Yourself 15 min

unsigned long t0 = millis();
WiFi.begin(SSID, PASSWORD);
while (WiFi.status() != WL_CONNECTED) delay(500);
unsigned long elapsed = millis() - t0;
Serial.print("# Connected in "); Serial.print(elapsed); Serial.println(" ms");

unsigned long start = millis();
while (WiFi.status() != WL_CONNECTED) {
  if (millis() - start > 30000) {
    Serial.println("# Connect timed out");
    return;       // give up for now, ensureWiFi() handles retries
  }
  delay(500);
}

#include <ESP8266WiFiMulti.h>     // or <WiFiMulti.h> on ESP32

ESP8266WiFiMulti wifiMulti;

void setup() {
  wifiMulti.addAP("Home", "homepass");
  wifiMulti.addAP("Phone", "phonepass");
  while (wifiMulti.run() != WL_CONNECTED) delay(500);
  Serial.print("# Connected to "); Serial.println(WiFi.SSID());
}

Mini-Challenge · Build a connection logger 10 min

Polish your sketch so it's a usable diagnostic tool for any future WiFi project.

1. Boot banner: SSID, IP, RSSI, MAC.
2. In loop(), every 30 seconds: print one line with current RSSI and connection status.
3. When disconnected: print one line per reconnect attempt.
4. When reconnected: print "# Reconnected after Xs (Y attempts)".

Save as wifi-diag.ino. First sketch to upload whenever a future project has connectivity problems — it tells you whether the issue is WiFi or higher up the stack (DNS, server, etc.).

Recap 5 min

WiFi.begin(SSID, password) + poll WiFi.status() == WL_CONNECTED = connected. Read the IP, gateway, RSSI, channel for diagnostics. Add a non-blocking ensureWiFi() at the top of loop() so the device survives router reboots and signal blips. Phone hotspot is the safest network for school work — no password leakage if you share code. 5 GHz isn't supported; corporate WPA-Enterprise isn't supported. Tomorrow we use the connection to actually fetch a web page — your first HTTP client.

SSID

Service Set Identifier — the human-readable network name ("Home-WiFi").

Station mode / Access Point mode

STA = client connecting to an existing router. AP = the board IS a router. WiFi.mode() selects.

DHCP

Dynamic Host Configuration Protocol — the router assigns an IP to each new device. The default; gives you a different IP each time.

Static IP

An IP you manually configure on the device, outside the router's DHCP pool. Lets you bookmark http://192.168.1.42 reliably.

Gateway

Your router's IP. The device sends all non-local traffic here.

MAC address

The board's unique 48-bit hardware ID. Used for DHCP reservations and some network ACLs.

RSSI

Signal strength in dBm. −30 dBm = excellent, −85 dBm = barely usable.

Reconnect logic

Code that automatically rejoins WiFi after a drop. Required for any unattended device.

WiFi.status()

Returns the current state of the WiFi state machine. Poll for WL_CONNECTED; switch on the others for diagnostics.

WiFiMulti

Helper that picks the strongest of several known networks. ESP8266WiFiMulti on ESP8266; WiFiMulti on ESP32.

Homework 5 min

1. Save the diagnostic sketch as wifi-diag.ino.
2. Note in your engineering notebook: your board's MAC, the IP it gets on your home network, the RSSI in your usual workspace.
3. Bring tomorrow: the board still wired up (or just on its USB cable — no other components needed for L03-31).
4. Read ahead to ARD-L03-31 (HTTP Client). Tomorrow we GET a real webpage.

Bring back next class:

• Working wifi-diag.ino with your credentials.
• MAC + IP + RSSI in your notebook.