Source: https://mokxi.com/parts/mq2 Updated: 2026-11-10 Part # Gas sensor, MQ-2 A heated tin-oxide element on a comparator board. It reads like a gas leak until it has warmed up. See every part - 4 pins - 5 settings - In 1 project - In 1 lesson Drawn live by the editor's own code, at the size you see it. At a glance ## The Gas sensor, MQ-2 in brief What it is, and every setting the properties panel gives it. The MQ-2 is a heated tin dioxide gas sensor, sold on an FC-22 style comparator board with four pins: VCC, GND, DO and AO. Its heater wants 5 volts and 150 mA, so it runs from an Uno’s 5 V pin, or from VIN or USB 5 V beside an ESP32, never from 3.3 V; a cold sensor’s AO can sit above 3.3 volts, so an ESP32 should read it through a divider. More gas lowers the sensor’s resistance and raises AO, and the LM393 pulls DO low and lights the lamp when AO passes the trimmer. Mokxi follows the datasheet’s log-log sensitivity curves for LPG, methane, hydrogen, smoke, alcohol and CO, with r0, rl, threshold and warmup properties and a slider to 10 000 ppm. With the 1 k load, 10 000 ppm of LPG reads only about 1.4 volts. A cold sensor reads as full of gas and settles over a 20 second warm-up, then follows the gas with time constants of 2 seconds arriving and 8 clearing, so an alarm on the first reading fires at every power-up. Humidity and gas mixtures are not modeled. Family Sensors Pins 4 gas lpg (or methane, hydrogen, smoke, alcohol, co) r0 10000 rl 1000 threshold 0.1 warmup 20 A circuit built around it, running and explained: the MQ-2 gas sensor simulator. Pins ## 4 pins Named as the editor names them, so a wire lands where you expect it. Pin Role What it does VCC Input or output Supply, 5 V. The heater is specified at 5.0 V. GND Input or output Ground. DO Output Low when the gas is past the trimmer. Open collector with a 10 k pull-up. AO Output The sensor over the load resistor: higher means more gas. How to use it ## How to use the MQ-2 gas sensor with an Arduino Wire VCC to 5 V, GND to GND and AO to A0; DO can go to any digital pin if you want the trimmer to decide. A higher analogRead() means more gas. On the board’s 1 k load clean air reads only about 11 counts once warm, so pick an alarm level from your own clean-air reading rather than from a tutorial’s number. Ignore the first 20 seconds. A cold element reads as if the room were full of gas, so a sketch that alarms on its first reading goes off at every power-up. Add a little hysteresis too: the gas leak detector sounds at 100 and only stops below 80, so a reading on the line does not chatter the buzzer. Part pin Board pin VCC 5 V GND GND AO A0 The heater needs 5 V on every board. On a 3.3 V board such as an ESP32, run it from the 5 V or VIN pin and bring AO down through a divider before the ADC. Click to open it in the editor This is the simulator itself, running here. Click anything to open it in the editor. Open this project in the editor Read the full tutorial How it is modeled ## What is true about the Gas sensor, MQ-2, here In its help article’s own words: what the simulation gets right, and where it stops. ### Modeled The curve. The datasheet plots Rs / R0 against concentration on log-log paper, one straight line per gas, with a flat line for clean air at about 9.8. Each gas here is two numbers read off that chart, the ratio at 200 ppm and the slope: Gas Rs / R0 at 200 ppm Slope hydrogen 2.1 -0.47 LPG 1.6 -0.47 methane 3.0 -0.38 alcohol 2.9 -0.37 smoke 3.4 -0.44 CO 5.2 -0.34 They are readings of a printed chart, good to the width of its lines; hydrogen comes out at a ratio of 1.0 at 1000 ppm, as the definition of R0 says it must. With the 1 k load resistor clean air reads only a few tens of millivolts, and even 10 000 ppm of LPG reads about 1.4 V: the useful range is the bottom third of the ADC. The warm-up. A cold MQ-2 reads low resistance, as if the room were full of gas. Switch it on and AO jumps up, DO trips, and over the warm-up the reading sinks to clean air. A sketch that raises the alarm on its first reading goes off every time it is powered, on the bench and here. Slow response. Once warm, the reading follows the gas with a time constant of 2 seconds when gas arrives and 8 seconds when it clears. A whiff is seen in a few seconds and takes half a minute to go away. ### Not modeled The datasheet asks for a 24 hour burn-in before any figure it gives is to be trusted; the 20 second warm-up is the part of that anyone watches, and it is a property. The heater draws about 150 mA, which is why a real one should not run from a board's 3.3 V pin; the supply here is not loaded by it. Humidity and temperature, which move a real reading by tens of percent, are not modeled, and there is one gas at a time. The comparator has no hysteresis, as on the real board. From MQ-2 gas sensor, in full. Projects ## See the Gas sensor, MQ-2 in a project One built-in project uses it. It opens in the editor, already wired. Lessons ## Where it turns up in a lesson One lesson places it in its own circuit. ### Learn articles 1 lesson - Arduino MQ-2 Gas Sensor: Wiring, Warm-Up and Code Libraries ## Arduino libraries for the Gas sensor, MQ-2 Built in, so the sketch compiles with nothing to install. Each page has the calls, the wiring and an example to run. - MQUnifiedsensor More parts ## The rest of the bench Every one of these is drawn and simulated the same way. Full-size breadboard A real 0.1 inch grid with the rails and the center channel, 63 columns wide. Jumper wires Drag from any pin or hole to any other. Corners snap, and you can drag them. Power A supply rail at the voltage you choose. Ground The other end of every circuit. LED Lights when current flows. Five colors, and the brightness is what your eye would see. Filament lamp A tungsten bulb in a holder: an inrush when it is switched on cold, tens of milliseconds to warm up, and dim on half its voltage. Resistor Any value you like, with the color bands drawn to match. ESP32-C3-DevKitM-1 A RISC-V board that runs your firmware at 160 MHz on the real memory map. Pushbutton A 12 mm tactile switch. Hold it while the simulation runs. Raspberry Pi Pico The RP2040 board on our own Cortex-M0+ core. Pick a program and press Run. Raspberry Pi Pico W Raspberry Pi Pico W (RP2040). The same board and the same pinout as a Pico, with the CYW43439 on it. The WiFi is simulated (no radio; real internet through the Cloud panel’s switch), and the on-board LED, which hangs off that chip rather than off GP25, is driven through the same path. Everything else is the Pico. Raspberry Pi 4 Model B Raspberry Pi 4 Model B: the 40-pin header, driven by main.py with RPi.GPIO or gpiozero. See every part ## Wire up the Gas sensor, MQ-2 Open the editor and push it into the breadboard. It is free, and it runs on your own machine. Start building free Open the editor