Build a Flame Sensor Alarm

Understand the target result

Read the flame sensor and create a demonstration-only visual and audible warning. The expected result is: The demonstration alarm responds to a controlled test source.

Prepare the board and parts

Disconnect the ESP32 from USB. Put the ESP32, breadboard, jumper wires, and the listed lesson parts in front of you. Straighten bent pins gently and never force a module into the breadboard.

Make each connection with power off

1. Sensor VCC → 3.3V and GND → GND.
2. Sensor analog output AO → GPIO 34.
3. Optional LED: GPIO 23 → 220Ω resistor → LED anode; cathode → GND.

Install any library and upload the code

No additional Arduino library is required for this starter sketch. Select your ESP32 board and serial port before clicking Upload.

const int SENSOR = 34, LED = 23;
int threshold = 2000;
void setup() { Serial.begin(115200); pinMode(LED, OUTPUT); }
void loop() {
  int value = analogRead(SENSOR);
  digitalWrite(LED, value > threshold);
  Serial.printf("Sensor: %d\n", value);
  delay(100);
}

Power the circuit and observe

Connect USB power only after the wiring check. Open Serial Monitor at 115200 baud when the sketch prints data. Watch the circuit for at least 20 seconds and compare it with this expected behavior: The demonstration alarm responds to a controlled test source.

Change one value and test again

Make one small change—such as a delay, threshold, brightness, or displayed message—then upload again. This confirms that you understand which part of the program controls the result.