38. GPIO, PWM, ADC and UART on ESP32

Project: Bench lamp dimmer

Build a small bench lamp control: pot sets brightness, Serial shows percent so you can match a desired level. Same skills later drive room lights over Wi-Fi (lesson 42) - start local and tactile.

Sketch 1 links pot to PWM duty. Sketch 2 is the product readout: Lab lamp brightness percent with millis-timed Serial.

Skills you already have

digitalWrite, analogWrite, analogRead and Serial still work. Write silkscreen GPIO numbers (2, 34), not Uno D-labels. Serial at 115200.

Pick pins that can do the job

GPIO 34-39 are input-only on classic ESP32 - pot yes, LED no. Course wiring: pot on 34, lamp LED / on-board LED on GPIO 2. Pot from 3V3.

PWM via LEDC / analogWrite

analogWrite(pin, duty) uses LEDC under the hood. map() converts 0-4095 pot codes into 0-255 duty.

int raw = analogRead(34);
int duty = map(raw, 0, 4095, 0, 255);
analogWrite(2, duty);

UART reminder

USB Serial is still Serial. Print brightness while you turn the pot so ADC and eye agree.

Wiring and safe build sequence

1. Pot outer legs -> 3V3 and GND; wiper -> GPIO 34
2. GPIO 2 -> 220-330 ohm -> LED anode; cathode -> GND (or on-board LED)
3. Serial Monitor 115200

What this sketch is for: Discovery: turn the pot and watch LED brightness track a 0-255 duty printed on Serial.

const int potPin = 34;
const int ledPin = 2;

void setup() {
  pinMode(ledPin, OUTPUT);
  Serial.begin(115200);
  analogReadResolution(12);
}

void loop() {
  int raw = analogRead(potPin);
  int duty = map(raw, 0, 4095, 0, 255);
  analogWrite(ledPin, duty);
  Serial.println(duty);
  delay(100);
}

What this sketch is for: Useful dimmer UI: same hardware, but Serial shows Lab lamp brightness as a percent updated every 200 ms with millis (no long delay). Match the breadboard layout below before upload.

const int potPin = 34;
const int lampPin = 2;
unsigned long lastPrint = 0;

void setup() {
  pinMode(lampPin, OUTPUT);
  Serial.begin(115200);
  analogReadResolution(12);
  Serial.println("Bench lamp dimmer");
}

void loop() {
  int raw = analogRead(potPin);
  int duty = map(raw, 0, 4095, 0, 255);
  analogWrite(lampPin, duty);

  if (millis() - lastPrint >= 200) {
    lastPrint = millis();
    int pct = map(duty, 0, 255, 0, 100);
    Serial.print("Lab lamp ");
    Serial.print(pct);
    Serial.println("%");
  }
}