What it shows
A Sharp GP2Y1010 optical dust sensor measures airborne particles by scattered infrared light. An Arduino logs the density, shows it on an LCD and switches a 12 V fan with a cloth filter through a relay when dust rises, a model of an air purifier.
The science
Inside the sensor an infrared LED flashes for 0.32 ms and a photodiode set at an angle sees only light scattered by particles crossing the beam. The Arduino must pulse the LED pin and read the analog output 0.28 ms after the pulse starts, which needs delayMicroseconds and careful timing. The output voltage rises about 0.5 V per 100 µg per cubic metre above a clean-air offset, so the sketch converts volts to density after measuring the offset in clean air. The fan runs through a relay when density passes a threshold and stops when it falls back.
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
- A Sharp GP2Y1010AU0F dust sensor with its 150 Ω resistor and 220 µF capacitor
- A 5 V relay module and a 12 V fan with adapter
- A 16x2 I2C LCD
- A piece of cloth or a car cabin filter scrap
- A clear box for the test chamber
- Jumper wires and a breadboard
Safety
For this project: Make dust with a pinch of flour puffed by an adult inside the closed box, and do not breathe it in; never use smoke or chemicals. The fan is 12 V DC 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 sensor per its datasheet: the LED pin through the 150 Ω resistor and the capacitor to 5 V, LED control to pin 7, output to A0.
Write the read function: set LED low (on), wait 280 µs, analogRead, wait 40 µs, set LED high (off), wait 9680 µs.
Average 20 such readings, convert to volts (reading times 5 divided by 1024) and print.
Measure in clean air for a minute to get the offset voltage, usually 0.6 to 0.9 V.
Convert to density: the sensor gives 0.5 V per 0.1 mg per cubic metre, so (volts minus offset) times 0.2 gives mg per cubic metre; show it on the LCD.
Wire the relay IN to pin 8 and the fan through COM and NO to its adapter, with the cloth filter taped over the intake.
Start the fan above 0.1 mg per cubic metre and stop below 0.05.
Place the sensor and fan in the clear box; puff a pinch of flour inside and watch the reading jump and the fan clear it.
Log density every five seconds to the serial monitor and plot how fast the fan cleans the box with and without the filter.
What you should see
Dust density rises sharply when flour is puffed and falls back over a few minutes while the fan runs; the plot shows faster clearing with the filter fitted.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01Why must the reading be taken 280 µs after the LED turns on?
The datasheet specifies the moment the output settles during the short pulse; reading earlier or later gives the wrong value.
02What do PM2.5 and PM10 mean?
Particles smaller than 2.5 and 10 micrometres; the small ones reach deep into the lungs.
03Why does the sensor need a capacitor and resistor?
They smooth the brief high-current LED pulse so it does not disturb the supply.
04How does a purifier filter work?
Air is forced through a fine fibre mat that traps particles while letting air pass.
Take it further
Replace the sensor with a PMS5003 laser sensor and compare the two readings side by side.
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.
Free ebooks for this project
Robotics
Arduino and Coding for Robots Study Book
The complete study notes, practice questions and glossary for Arduino and Coding for Robots
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