What it shows
An infrared flame sensor module detects the near-infrared light given out by a flame from up to about half a metre away. The Arduino sounds an alarm and runs a 5 V submersible pump through a relay so a tiny sprinkler sprays water on the model store room.
The science
A flame gives off strong infrared light near 760 to 1100 nm. The sensor is a photodiode filtered for that band, with a comparator that pulls its digital pin low when the light passes a level set by the on-board screw. The Arduino reads that pin, and the analog pin gives a rough distance. Because the pump motor draws more current than a pin can supply, a relay switches it. A short confirmation delay avoids triggering on a brief flash; strong sunlight can still fool the sensor, so it is used indoors.
Materials
Cost: under Rs 1,500. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- An Arduino Uno clone and USB cable
- An IR flame sensor module (single or 5-way)
- A 5 V submersible mini pump with plastic tube
- A 5 V relay module
- A buzzer and a red LED with a 220 Ω resistor
- A plastic tray, a small water tub and a cardboard model room
- Jumper wires
Safety
For this project: An adult must handle the candle, standing it on a metal tray at least 30 cm from the cardboard model, with a bowl of water or a damp cloth ready. Keep water away from the Arduino and never leave the candle unattended. The pump runs on 5 V only.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
Step by step
9 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Wire the flame sensor: VCC to 5 V, GND to GND, DO to pin 2, AO to A0.
Wire the buzzer to pin 5, the LED through its resistor to pin 6, and the relay IN to pin 7.
Connect the pump through the relay COM and NO terminals to a separate 5 V source such as a power bank, with grounds joined.
Place the pump in the water tub and run the tube to a pinholed cap above the model room as the sprinkler.
Write a sketch that reads DO; if it stays low for 300 milliseconds, start the buzzer, LED and relay for ten seconds.
Print the A0 value so you can show the reading rising as the candle comes closer.
Turn the sensor screw until a candle at about 50 cm triggers it but a bright LED ceiling light does not.
Have an adult stand a lit candle on a metal tray about 30 cm from the sensor, clear of the cardboard: the buzzer sounds and the pump sprays the model room.
Add a reset button on pin 3 that silences the alarm after the pump cycle.
What you should see
A candle flame within about half a metre triggers the alarm and a ten-second spray; ordinary LED room lighting does not.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01Why does ordinary room lighting not trigger the sensor?
LED and fluorescent lamps give out almost no infrared and the threshold is set above what a distant lamp gives. Sunlight and filament bulbs can trigger it, so the sensor suits indoor use.
02What does the on-board screw change?
The reference voltage of the comparator, which sets how much infrared is needed to pull the digital pin low.
03Why wait 300 milliseconds before acting?
To ignore brief flashes such as a camera or reflection; a real flame stays detected.
04Why keep the pump supply separate?
The motor draws current spikes that could reset the Arduino if they share the USB 5 V line.
Take it further
Use a 5-way flame sensor array and turn a servo so the sprinkler points towards the strongest reading.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
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