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Building a Carbon Monoxide Detector
Ed

Ṣẹ́dá nipasẹ̀

Ed

13. Oṣù Keje 2026FI
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Building a Carbon Monoxide Detector

Build a circuit that senses carbon monoxide (CO) — the invisible, odourless gas from any incomplete combustion — and raises an alarm when it rises. An MQ-7 sensor gives the Arduino a reading that climbs with CO; the code compares it to a clean-air baseline and triggers a buzzer and red LED. A great way to learn gas sensing — but read the safety note: this is a demonstration, NOT a certified life-safety CO alarm.

Àárín
1-2 hours

Ìlànà

1

Wire the sensor, buzzer and LED

On the breadboard: MQ-7 VCC to Arduino 5V, GND to GND, and its analog output (AOUT) to Arduino A0. Active buzzer + to pin 8, - to GND. Red LED anode to pin 7 through a 330 Ω resistor, cathode to GND.

Àwọn ohun èlò fún ìgbésẹ̀ yìí:

Arduino Uno R3Arduino Uno R31 ẹyọ
Carbon Monoxide Sensor - MQ-7Carbon Monoxide Sensor - MQ-71 ẹyọ
Modulu buzzer tí ń ṣiṣẹ́Modulu buzzer tí ń ṣiṣẹ́1 ẹyọ
LED - Basic 5mmLED - Basic 5mm1 ẹyọ
Resistor 330 Ohm 1/6 Watt PTH - 20 packResistor 330 Ohm 1/6 Watt PTH - 20 pack1 ẹyọ
BreadboardBreadboard1 ẹyọ
Jumper Wires (Male-to-Male)Jumper Wires (Male-to-Male)1 àkópọ̀
2

Connect and open the IDE

Plug the Arduino into your computer with the USB cable, open the Arduino IDE, and select Arduino Uno and its serial port.

Àwọn ohun èlò fún ìgbésẹ̀ yìí:

USB-B CableUSB-B Cable1 ẹyọ

Àwọn irinṣẹ́ tí a nílò:

Kọ̀ǹpútà Tí Ó Ní Arduino IDEKọ̀ǹpútà Tí Ó Ní Arduino IDE
3

Upload the detector sketch

Paste this sketch and upload. It warms the sensor for two minutes, records a clean-air baseline, then sounds the buzzer and lights the LED whenever the reading climbs above that baseline.

co_detector.inoarduino
// Carbon monoxide INDICATOR using an MQ-7 sensor.
// NOT a certified life-safety alarm - see the blueprint's safety note.
// MQ-7 analog output on A0; buzzer on pin 8; red warning LED on pin 7.

const int MQ7_PIN = A0;
const int BUZZER_PIN = 8;
const int LED_PIN = 7;

int cleanAirValue = 0;          // baseline, measured at startup
const int ALARM_MARGIN = 150;   // how far above baseline triggers the alarm

void setup() {
  pinMode(BUZZER_PIN, OUTPUT);
  pinMode(LED_PIN, OUTPUT);
  Serial.begin(9600);

  Serial.println("Warming up the MQ-7 (2 min) in clean air...");
  delay(120000);                // 2-minute warm-up
  cleanAirValue = analogRead(MQ7_PIN);
  Serial.print("Clean-air baseline: ");
  Serial.println(cleanAirValue);
}

void loop() {
  int reading = analogRead(MQ7_PIN);
  Serial.println(reading);

  if (reading > cleanAirValue + ALARM_MARGIN) {
    digitalWrite(LED_PIN, HIGH);      // CO above baseline -> alarm
    digitalWrite(BUZZER_PIN, HIGH);
  } else {
    digitalWrite(LED_PIN, LOW);
    digitalWrite(BUZZER_PIN, LOW);
  }
  delay(500);
}
4

Warm up, baseline and test

Power it in fresh air and let the 2-minute warm-up set the clean-air baseline (a brand-new MQ-7 also needs a longer 24–48 h burn-in before its readings settle). Then hold a small CO source nearby in a ventilated room — the smoke from a just-blown-out match works — and the buzzer and LED should trigger. Change ALARM_MARGIN to make it more or less sensitive.

5

Important safety limits

This is a LEARNING project and, at best, a supplementary indicator — it is NOT a certified life-safety device. A hobby MQ-7 gives a relative reading, not a calibrated ppm; it drifts over time and needs regular re-baselining, and it also responds to smoke and other gases. Carbon monoxide is invisible, odourless and can be fatal: for real protection always use a UL- or EN-certified CO alarm. Never rely on this circuit to keep anyone safe.

Àwọn ohun-èlò

8

Àwọn irinṣẹ́ tó nílò

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Àpapọ̀ Ìfojúsùn
Ohun tí ẹni tó ṣe é rà. Àwọn ohun èlò tí kò ní iye owó ni o máa rà níbi tí o bá ti rà á.
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