Air Quality Sensor Setup

I looked at 7 low-cost air quality sensors using the setup described below. Most of these require a 48hour preheating period, so I kept them on for a few days before testing the output. You can check out what the preliminary sensor output looks like in several different locations.

MQ-7 (Datasheet)

Carbon Monoxide Sensor
Datasheet requires a heating on/off cycle (but I did not implement it)
Sensor is symmetric (A and B sides are interchangeable)
I chose 2.7K as my RL

 

MQ-131 (Datasheet)

Ozone Sensor
Sensor is symmetric (A and B sides are interchangeable)
I chose 10K as my RL

 

 

GP2Y 1010AU0F (Datasheet)

Dust Sensor
I ordered a 6-pin connector (Tyco Part #2058943-5) to avoid the fragile soldering
In the diagram the pins are ardered from left to right as shown in the photograph
The LED pin has to be modulated with a cycle of 1ms as discussed in the datasheet.
The LED seems to use a PNP transistor so to power on, the LED pin must actually recieve a lower voltage.
Sample Arduino code:

digitalWrite(ledPower,LOW); // Power on the LED
// ledPower is any digital pin on the arduino connected to Pin 3 on the sensor

delayMicroseconds(280);
dustVal = analogRead(dustPin); // read the dust value via pin 5 on the sensor
delayMicroseconds(60);
digitalWrite(ledPower, HIGH); // turn the LED off
delayMicroseconds(9680);

TGS 2442(Datasheet)

Another carbon monoxide sensor
This sensor has 2 separate power cycles (heating and sensing circuits)

Sample Arduino code:

int figaroHeater = 6; // Heat VCC
int figaroCircuit = 5; // Sensing VCC

digitalWrite(figaroCircuit, LOW); // turn off sensing VCC
analogWrite(figaroHeater, 245); // turn on heating (recommended 4.8 volts)
delay(14);
analogWrite(figaroHeater, 0); // turn off heating
delay(981);
digitalWrite(figaroCircuit, HIGH);
delay(3)
figaroCOVal = analogRead(figaroCOPin); // take measurement here
delay(2);

 

TGS 2620(Datasheet)

Solvent vapor (VOC) sensor
I found that it also reacts to traffic exhaust and combustion
Really simple circuit, I chose 39 K as my RL

MQ-135(Datasheet)

General purpose ammonial, benzene and other harmful chemicals(VOC) sensor
Symmetric pin-out (A and B sides are interchangeable)
I chose 39K as my RL

TGS 2201(Datasheet)

Dual-purpose diesel and exhaust sensor

R1 is the load resistance of terminal 3 (exhaust output), which I chose to be 10K

R2 is the load resistance for terminal 1 (diesel output), which I chose to be 120K