Lesson 4 of 4

Switch an LED over Wi-Fi

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// A web server that switches the LEDs from a browser #include <ESP8266WiFi.h> #include <ESP8266WebServer.h> const char* ssid = "iynk-guest"; const char* password = ""; // this network has no password const int LED_PIN = D1; ESP8266WebServer server(80); void handleRoot() { server.send(200, "text/plain", "NodeMCU: try /on or /off"); } void handleOn() { digitalWrite(LED_PIN, HIGH); digitalWrite(LED_BUILTIN, LOW); // LOW lights the blue LED server.send(200, "text/plain", "LED on"); } void handleOff() { digitalWrite(LED_PIN, LOW); digitalWrite(LED_BUILTIN, HIGH); server.send(200, "text/plain", "LED off"); } void setup() { Serial.begin(115200); pinMode(LED_PIN, OUTPUT); pinMode(LED_BUILTIN, OUTPUT); digitalWrite(LED_BUILTIN, HIGH); WiFi.mode(WIFI_STA); // station mode: join a network as a client WiFi.begin(ssid, password); Serial.print("Connecting"); while (WiFi.status() != WL_CONNECTED) { delay(500); // connecting takes about a second Serial.print("."); } Serial.println(); Serial.print("IP address: "); Serial.println(WiFi.localIP()); server.on("/", handleRoot); server.on("/on", handleOn); server.on("/off", handleOff); server.begin(); Serial.println("HTTP server started"); } void loop() { server.handleClient(); // answer browser requests all the time }

Stopped · Your code isn't running yet. Until you press Run, the board runs the program already on it.

Nothing printed yet. Press Run.

Join a Wi-Fi network, start a web server on port 80 and switch the LEDs from a phone with /on and /off.

Joining a Wi-Fi network
A web server with three pages
Why the supply matters for Wi-Fi

Pin	Connects to	What it does
`D1`	220 Ω resistor and the yellow LED	output, HIGH = on
`D4`	blue LED on the ESP-12E	output, LOW = on
`GND`	LED cathode	ground

Wire it in

Sensors and actuators this board drives, with the real connections.

LEDSupply 3.3 V
A 220 Ω resistor gives a red LED about 6 mA from a 3.3 V pin: (3.3 V - 2.0 V) / 220 Ω.
Part pin Board pin
anode (long leg), through 220 Ω D1Wire colour orange
cathode GNDWire colour black
Careful
Never connect an LED without a resistor: the pin is rated 12 mA. Blue and white LEDs need about 3 V and stay dim on 3.3 V.

All 12 parts on the NodeMCU (ESP8266) page

Connects to

What it does

D1

220 Ω resistor and the yellow LED

output, HIGH = on

D4

blue LED on the ESP-12E

output, LOW = on

GND

LED cathode

ground

Wire it in

Sensors and actuators this board drives, with the real connections.

LEDSupply 3.3 V

A 220 Ω resistor gives a red LED about 6 mA from a 3.3 V pin: (3.3 V - 2.0 V) / 220 Ω.

Part pin	Board pin
anode (long leg), through 220 Ω	D1Wire colour orange
cathode	GNDWire colour black

Careful

Never connect an LED without a resistor: the pin is rated 12 mA. Blue and white LEDs need about 3 V and stay dim on 3.3 V.

All 12 parts on the NodeMCU (ESP8266) page

Switch an LED over Wi-Fi

Try it yourself

Serial monitor

Checks

Break it

Inputs

Parameters

Wire it in

Switch an LED over Wi-Fi

Try it yourself

Serial monitor

Checks

Break it

Inputs

Parameters

Wire it in