There are some low cost analyzers  for about $15US. For home or test projects these sensors are great but I wouldn’t recommend them for any serious environmental studies. (For true air quality monitoring you need to compensate for temperature and humidity).

For this projects we used a 90mA PM2.5 Dust Sensor PPD42NS / PPD42NJ Sensor. These sensor need to be mounted upright, so we used some Meccano to build a simple stand.

The sensors have 5 pins, with the pinouts of:

• Pin 1  => GND
• Pin 3  => 5 VDC
• Pin 4  => Data Pin

To see the results we used a 16×2 LCD shield.

The product example samples every 30 seconds and it returns a value of particles per 1/100 of a cubic foot (pcs/0.01cf).

The returned values (in pcs/0.01cf) will need some validation but from our testing we found that :

• 0-500 pcs/0.01cf = a clear room
• 500-1500 pcs/0.01cf = a “fairly” clean room
• 1500-4000 pcs/0.01cf = a room in need of dusting (but not super dusty)
• 4000+ pcs/0.01cf = if you have allergies you may notice the room

Our code for the project is:

90mA PM2.5 Dust Sensor PPD42NS / PPD42NJ Sensor with an 16x2 LCD Shield

JST Pin 1 (Black Wire) => Arduino GND
JST Pin 3 (Red wire) => Arduino 5VDC
JST Pin 4 (Yellow wire) => Arduino Digital Pin 8
*/
#include <LiquidCrystal.h>
LiquidCrystal lcd(8, 9, 4, 5, 6, 7);

int pin = 28;
unsigned long duration;
unsigned long starttime;
unsigned long sampletime_ms = 30000;
unsigned long lowpulseoccupancy = 0;
float ratio = 0;
float concentration = 0;
float maxcon = 0;

void setup() {
 Serial.begin(9600);
 pinMode(8,INPUT);
 starttime = millis();
 lcd.begin(16, 2);
}
void loop() {
 duration = pulseIn(pin, LOW);
 lowpulseoccupancy = lowpulseoccupancy+duration;
 if ((millis()-starttime) > sampletime_ms)
 {
 ratio = lowpulseoccupancy/(sampletime_ms*10.0); // Integer percentage 0=>100
 concentration = 1.1*pow(ratio,3)-3.8*pow(ratio,2)+520*ratio+0.62;
 if (concentration > maxcon){ maxcon = concentration;}
 lcd.setCursor(0, 0);
 lcd.print("now: ");
 lcd.setCursor(5, 0);
 lcd.print(concentration);
 
 lcd.setCursor(0, 1);
 lcd.print("max: ");
 lcd.setCursor(5, 1);
 lcd.print(maxcon);

 Serial.print(" concentration: ");
 Serial.print(concentration);
 Serial.println(" pcs/0.01cf");
 Serial.print(" max concentration: ");
 Serial.print(maxcon);
 Serial.println(" pcs/0.01cf");
 lowpulseoccupancy = 0;
 starttime = millis();
 }
}