Unit I - ESP32 Advanced

50. Capstone: Networked Room Node

Build an assessment-ready room node: STA WiFi, live comfort reading on the web, JSON for programs, and a threshold alert LED.

Estimated time 4-5 hours

Learning outcomes

Integrate STA WiFi, ADC sensing and WebServer into one reliable room node
Serve a live HTML dashboard and a /json reading
Drive an alert LED from a calibrated threshold
Follow sense -> decide -> connect -> serve integrate order
Demonstrate and explain the system at pass level without MQTT/NeoPixel/OTA

Parts and preparation

ESP32 DevKit, USB data cable, 10 k ohm potentiometer on GPIO 34 (room comfort / level stand-in), LED + series resistor on GPIO 2 (alert lamp), breadboard and jumpers. Libraries: WiFi + WebServer only (esp32 core).

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.
`WebServer.h`	WebServer	Espressif	Built into the esp32 Arduino core.

Capstone: Networked Room Node instructional connection diagram

Project: Networked room node

Build a small room monitor you could leave on a bench: anyone on the same WiFi opens a page, sees a live comfort level (potentiometer standing in for light, CO2 proxy, or knob setpoint), and an alert LED lights when the level crosses your threshold.

Pass requires a reliable demo and a clear explanation - not every Unit I feature at once. MQTT, NeoPixel status tiles, deep sleep and OTA are stretch only after the node is solid.

ESP32 STA room node with pot, web page and threshold LED — Sense a level, decide alert, serve HTML and JSON on the LAN.

Integrate in order

1) Power and 3.3 V pot (never 5 V into ADC). 2) Sense: Serial-print analogRead on GPIO 34. 3) Decide: threshold drives alert LED. 4) Connect: STA, print IP. 5) Serve: / for humans, /json for programs. 6) Loop: sample + handleClient, no long delay.

If something fails, isolate the last block that worked.

Block	Pass evidence
Sense	Page/Serial value moves with the pot
Decide	Alert LED flips near your threshold
Connect	LAN IP printed; phone on same SSID
Serve	Dashboard updates; /json matches

GPIO 34 and ADC with WiFi

GPIO 34 is ADC1 input-only on classic DevKits - correct while WiFi runs. analogRead is 0-4095 at 12-bit. Calibrate threshold by watching live values. The pot is a stand-in: say in your demo what real sensor you would swap in later.

Signal	Wiring
Pot ends	3V3 and GND
Pot wiper	GPIO 34
Alert LED	GPIO 2 via resistor

HTML dashboard and JSON

Humans get / with room name and meta refresh. Programs get /json: {"room":"Lab room","level":2048,"threshold":2000,"alert":true}. String building is enough - ArduinoJson optional stretch.

Assessment rubric (pass level)

Reliable demo first. Extra features do not rescue a flaky node.

Criterion	What good looks like
Bring-up	IP on Serial; correct board/port
Dashboard	Live level as pot turns
Alert	LED tracks threshold clearly
JSON	/json matches the page
Safety	3V3 pot; series LED resistor
Explain	STA, handleClient, ADC1 in your words
Fault-find	Isolate wiring vs WiFi vs code

Stretch only after a pass

Not required: MQTT publish (44), NeoPixel status colour (39-40), deep sleep pulses (47), OTA field updates (49), SoftAP setup (45). Pick at most one stretch.

Wiring and safe build sequence

Potentiometer: 3V3 -> one end, GND -> other end, wiper -> GPIO 34
Alert LED: GPIO 2 -> 220-330 ohm -> LED anode; cathode -> GND
USB for power; phone/PC on the same WiFi as the ESP32

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: Networked room node

Download .ino sketch

What this sketch is for: Full pass demo in one sketch: join WiFi, show Lab room comfort level on / and /json, light the alert LED above threshold. Calibrate threshold to your pot before the assessment. Match the breadboard layout below before upload.

Breadboard layout for ESP32 networked room node: potentiometer on GPIO 34 and alert LED on GPIO 2 — Breadboard for the capstone node: pot outer legs to 3V3 and GND, wiper to GPIO 34 (ADC1); alert LED with series resistor on GPIO 2 to GND. Click to enlarge.

#include <WiFi.h>
#include <WebServer.h>

const char* ssid = "YOUR_WIFI_SSID";
const char* password = "YOUR_WIFI_PASSWORD";
const char* roomName = "Lab room";

const int potPin = 34;
const int alertPin = 2;
const int threshold = 2000;

WebServer server(80);
int level = 0;
bool alertOn = false;

String getHTML() {
  String html = R"=====(
<!DOCTYPE html>
<html>
<head>
  <meta http-equiv="refresh" content="2">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Room node</title>
  <style>
    body { font-family: sans-serif; text-align: center; margin-top: 40px; }
  </style>
</head>
<body>
  <h1>)=====";
  html += roomName;
  html += R"=====(</h1>
  <p>Comfort level: )=====";
  html += String(level);
  html += R"=====(</p>
  <p>Alert threshold: )=====";
  html += String(threshold);
  html += R"=====(</p>
  <p>Alert lamp: )=====";
  html += alertOn ? "ON" : "OFF";
  html += R"=====(</p>
  <p><a href="/json">/json</a></p>
</body>
</html>
)=====";
  return html;
}

void handleRoot() {
  server.send(200, "text/html", getHTML());
}

void handleJson() {
  String body = "{"room":"";
  body += roomName;
  body += "","level":";
  body += String(level);
  body += ","threshold":";
  body += String(threshold);
  body += ","alert":";
  body += alertOn ? "true" : "false";
  body += "}";
  server.send(200, "application/json", body);
}

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

  WiFi.mode(WIFI_STA);
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println();
  Serial.print("Room node - open http://");
  Serial.println(WiFi.localIP());

  server.on("/", handleRoot);
  server.on("/json", handleJson);
  server.begin();
}

void loop() {
  level = analogRead(potPin);
  alertOn = level > threshold;
  digitalWrite(alertPin, alertOn ? HIGH : LOW);
  server.handleClient();
}

How the code works

roomName appears on the dashboard - change it for your assessment label.
threshold 2000 is a starting point on 12-bit ADC - calibrate live.
meta refresh updates humans; /json serves programs.
No long delay() - handleClient stays responsive.
Build from the breadboard photo: pot on GPIO 34, alert LED on GPIO 2.

Test and record evidence

Expected result: Serial shows the IP. Browser dashboard for Lab room updates as the pot turns. /json matches level/threshold/alert. Alert LED is clearly on above threshold and off below. You can explain STA, handleClient, and why GPIO 34 (ADC1) was chosen.

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

ADC stuck: 3V3 pot, wiper on GPIO 34, common GND.
Page static: same SSID as phone; exact IP from Serial.
Alert always on/off: recalibrate threshold.
WiFi fail: 2.4 GHz credentials as in Unit H.

Extension challenge: After a pass: publish level on MQTT, or map level to a NeoPixel status colour. Do not risk the pass demo for stretch features.

Check your understanding

Q1. What are you building?

Show answer

A networked room node with live web level and threshold alert.

Q2. Which WiFi mode?

Show answer

Station (STA) on the lab router.

Q3. Why GPIO 34?

Show answer

ADC1 input-only pin suitable with WiFi on classic ESP32.

Q4. Why not 5 V on the pot?

Show answer

ESP32 ADC is 3.3 V class.

Q5. What does /json provide?

Show answer

Machine-readable room, level, threshold, alert.

Q6. Why call handleClient every loop?

Show answer

Serve browsers while still sampling.

Q7. Is MQTT required to pass?

Show answer

No - stretch only.

Q8. What should a pass demo prove?

Show answer

Live dashboard, matching JSON, alert LED, and a clear STA/ADC explanation.

Q9. Integrate order first step after power?

Show answer

Sense on Serial before adding WiFi and the web UI.