FREE SIMULATOR EXAMPLE · BEGINNER

Pico W — IoT relay web server

This example turns a Pico W into an IoT relay controller: hit http://10.13.37.42/on and the relay on GP2 closes, switching an LED on a separate circuit. The classic web-controlled switch — WiFi join, HTTP server, one GPIO, one relay.

Board	Raspberry Pi Pico W (RP2040 + WiFi)
Difficulty	beginner
Category	communication
Libraries	None — just the Arduino core
Runs in	Sensbench browser simulator — free, no account

The exact circuit you get when you open this example — already wired, ready to run.

The MicroPython script

# main.py
# IoT Relay Control Web Server — MicroPython
#
# A blocking-style HTTP server on port 80 that flips a relay on
# GP2 in response to GET /on and GET /off. The server runs on the
# IP that the emulator hands out (10.13.37.42).

import network
import socket
import machine
import time

relay = machine.Pin(2, machine.Pin.OUT)
# Active-high so the LED wired to GP2 on the canvas lights when ON.
relay_state = 0
relay.value(relay_state)

ssid = "SENSBENCH-GUEST"
password = ""

wlan = network.WLAN(network.STA_IF)
wlan.active(True)
wlan.connect(ssid, password)

print("Connecting...")
while not wlan.isconnected():
    time.sleep(0.5)

ip = wlan.ifconfig()[0]
print("Connected at:", ip)

s = socket.socket()
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.bind((ip, 80))
s.listen(1)

print("Open browser: http://%s/" % ip)

def page():
    on = (relay_state == 1)
    color = "#22c55e" if on else "#666"
    label = "RELAY ON" if on else "RELAY OFF"
    return ("<html><head><meta name=viewport content='width=device-width,initial-scale=1'></head>"
            "<body style='font-family:sans-serif;text-align:center;padding:24px;background:#fafafa'>"
            "<h2>Pico W Relay (GP2)</h2>"
            "<div style='margin:18px auto;width:170px;padding:26px 0;border-radius:14px;"
            "background:%s;color:#fff;font-size:24px;font-weight:bold'>%s</div>"
            "<button style='font-size:18px;padding:12px 28px;margin:6px' "
            "onclick=\"fetch('on').then(()=>location.reload())\">ON</button>"
            "<button style='font-size:18px;padding:12px 28px;margin:6px' "
            "onclick=\"fetch('off').then(()=>location.reload())\">OFF</button>"
            "</body></html>") % (color, label)

# Wrap each client in try/except: a browser that drops the connection
# mid-response would otherwise raise ECONNRESET and kill the server loop.
while True:
    try:
        conn, addr = s.accept()
        request = str(conn.recv(1024))
        if "/on" in request:
            relay_state = 1; relay.value(relay_state)
        elif "/off" in request:
            relay_state = 0; relay.value(relay_state)
        conn.send("HTTP/1.1 200 OK\r\nContent-Type: text/html\r\n\r\n" + page())
        conn.close()
    except OSError:
        try:
            conn.close()
        except Exception:
            pass

How it works

The script joins SENSBENCH-GUEST and runs a blocking HTTP server on port 80. GET /on energizes the relay on GP2, GET /off releases it, and the server replies with plain text. The relay’s contacts switch a separate LED circuit — the isolation pattern a real relay exists to provide.

The server loop is deliberately simple: accept, parse the first line, act, respond, close. At 9600-baud-class simplicity it handles one client at a time, which is honest for a demo but the exact limitation the async example exists to solve.

Before you build it for real

Get the parts

Related examples

FAQ

Why does the server respond on 10.13.37.42?

That is the IP address the emulated WiFi network hands to the Pico W — a simulated LAN segment. On real hardware your router assigns a DHCP address instead, and you would read it from the serial console or your router’s client list. The fixed address keeps the demo deterministic.

Can a real relay be driven directly from GP2?

No. A relay coil needs tens of milliamps — beyond the RP2040’s 12 mA per-pin budget. The simulator’s relay is a virtual component; a real build needs a transistor driver between the pin and the coil, plus the flyback diode across it. The relay example page in this collection shows the pattern.