Overview

The KY-026 is an infrared (IR) flame and fire detection sensor module from the Keyes 37-in-1 sensor kit series. Engineered to detect naked flames, lighter fire, and combustion sources, it incorporates a high-speed black epoxy-encapsulated NPN phototransistor tuned to infrared light wavelengths between 760 nm760\text{ nm} and 1100 nm1100\text{ nm} (the primary IR emission spectrum of open flames).

The module pairs the IR photodiode with an LM393 differential voltage comparator and a multi-turn sensitivity potentiometer. It provides two output channels: a continuous analog voltage output (AO) for proximity/intensity estimation, and a digital threshold output (DO) that pulls Low when IR intensity exceeds the potentiometer setpoint. It is widely used in fire-fighting mini-sumo robots, stove safety alarms, and flame monitoring.

Quick reference

Operating voltage (VCC)3.3 V to 5.5 V DC
Spectral sensitivity760 nm760\text{ nm} to 1100 nm1100\text{ nm} (peak sensitivity at 940 nm940\text{ nm})
Detection angle60∘60^\circ directional cone
Detection distanceUp to 80 cm80\text{ cm} to 100 cm100\text{ cm} (for a standard lighter flame)
OutputsDual Analog Voltage (AO) & Digital LM393 Comparator (DO)
Onboard indicatorsPower LED (red) + Digital Alarm Output LED (green)
Operating current15 mA15\text{ mA} typical

Pinout

Standard 4-pin 0.1" (2.54 mm) breakout module header:

PinNameTypeDescription
1AOAnalog OutputAnalog voltage output (voltage drops as flame IR intensity increases)
2GNDPowerGround reference (0 V)
3VCC / +PowerSupply input (+3.3 V to +5.5 V DC)
4DODigital OutputLM393 comparator digital output (Low when flame detected)

Specifications

ParameterSymbolMinTypMaxUnitConditions
Supply VoltageVCCV_{CC}3.35.05.5VDC
Peak Wavelengthλpeak\lambda_{peak}—940—nmFire/flame IR spectrum
Spectral Bandwidthλrange\lambda_{range}760—1100nmResponse range
Detection Angleθ\theta—60—degHalf-sensitivity angle
Lighter Flame DistanceDistflameDist_{flame}1050100cmStandard lighter flame in dark room
Response Timetrest_{res}—15—µsPhototransistor response time

Operating Principle & Signal Behavior

  • No Flame / Dark: Photodiode conductivity is near zero (Rdark>1 MΩR_{dark} > 1\ \text{M}\Omega). Analog output AO sits near VCCV_{CC} (∼5V\sim 5\text{V}), and DO is High (VCCV_{CC}).
  • Flame Present: IR radiation from the flame increases photodiode conductivity, drawing current through the onboard pull-down resistor. Analog voltage AO drops towards 0V. When AO drops below the threshold set by the trimmer potentiometer, DO switches Low (0V) and the green LED illuminates.

VAO∝1Flame IR IntensityV_{AO} \propto \frac{1}{\text{Flame IR Intensity}}

Wiring

KY-026 Pin→Arduino UnoESP32Notes
VCC (+)5V / 3.3V3.3VPower rail
GNDGNDGNDSystem ground
AOAnalog Pin A0VP / GPIO36 (ADC1)Analog flame intensity signal
DODigital Pin D2GPIO 4Digital threshold trigger
Warning

Sunlight & Incandescent Light False Triggers:

  • Direct sunlight, halogen bulbs, and incandescent light bulbs emit significant 760–1100 nm760\text{--}1100\text{ nm} IR radiation, triggering false positives on the KY-026. Keep the sensor shielded from direct sunlight or calibrate the potentiometer threshold under ambient room lighting.

Example

cpp
const int flameAnalogPin = A0;
const int flameDigitalPin = 2;
const int buzzerPin = 13;

void setup() {
  Serial.begin(9600);
  pinMode(flameDigitalPin, INPUT);
  pinMode(buzzerPin, OUTPUT);
}

void loop() {
  int rawAnalog = analogRead(flameAnalogPin);
  int digitalVal = digitalRead(flameDigitalPin);

  float voltage = (rawAnalog / 1023.0) * 5.0;

  Serial.print("Analog AO: "); Serial.print(rawAnalog);
  Serial.print(" ("); Serial.print(voltage); Serial.print(" V)\t| Digital DO: ");

  if (digitalVal == LOW) {
    Serial.println("FLAME DETECTED! ALARM ON!");
    digitalWrite(buzzerPin, HIGH);
  } else {
    Serial.println("Safe (No Flame)");
    digitalWrite(buzzerPin, LOW);
  }

  delay(200);
}

Common mistakes

  • Inverting analog logic: Remember that lower analog voltages mean HIGHER flame intensity. A reading near 0V indicates an intense flame right in front of the photodiode.
  • Melting the photodiode lens: The black epoxy photodiode lens is plastic. Do not hold an open lighter flame closer than 10 cm10\text{ cm} to prevent melting the lens.

Notes

  • KY-026 vs MQ-2: KY-026 detects optical IR flame radiation instantly (15 μs15\ \mu\text{s} response); MQ-2 detects combustible gas concentrations (LPG, smoke, propane) via chemical reaction.

Assets & downloads