Air quality click

Air quality click is a simple solution for adding a high sensitivity sensor for detecting a variety of gases that impact air quality in homes and offices. It carries an MQ-135 sensor. The click is designed to run on a 5V power supply. It communicates with the target microcontroller over the AN pin on the mikroBUS™ line.

Detecting gases

Air quality click is suitable for detecting ammonia (NH3), nitrogen oxides (NOx) benzene, smoke, CO2 and other harmful or poisonous gases that impact air quality. The MQ-135 sensor unit has a sensor layer made of tin dioxide (SnO2), an inorganic compound which has lower conductivity in clean air than when polluting gases are present.

Calibration potentiometer

To calibrate Air quality click for optimum performance, use the on-board potentiometer to adjust the load resistance on the sensor circuit.

Key features

• MQ-135 sensor
  • SnO2 gas sensing layer
• Interface: AN
• 5V power supply

Specification

Pinout diagram

This table shows how the pinout on Air quality click corresponds to the pinout on the mikroBUS™ socket (the latter shown in the two middle columns).

Notes	Pin	mikroBUStm				Pin	Notes
Analog	AN	1	AN	PWM	16	NC	Not connected
Not connected	NC	2	RST	INT	15	NC	Not connected
Not connected	NC	3	CS	TX	14	NC	Not connected
Not connected	NC	4	SCK	RX	13	NC	Not connected
Not connected	NC	5	MISO	SCL	12	NC	Not connected
Not connected	NC	6	MOSI	SDA	11	NC	Not connected
Not connected	NC	7	3.3V	5V	10	+5V	Power supply
Ground	GND	8	GND	GND	9	GND	Ground

Programming

Code examples for Air quality click, written for MikroElektronika hardware and compilers are available on Libstock.

Code snippet

The following code snippet intitializes the LCD display, pins, and ADC, and then periodically calculates ppm value, and prints it to the LCD.

01 void main() {
02
03  LCD_Init();                                // Initialize Lcd
04  Lcd_Cmd(_LCD_CLEAR);                       // Clear display
05  Lcd_Cmd(_LCD_CURSOR_OFF);                  // Cursor off
06  Lcd_Out(1,1,"AirQuality click");           // Write text in first row
07
08  ANSELA = 0x04;                             // Set ADC on RA2
09  TRISA  = 0x04;                             // Set RA2 as input
10  LATA   = 0;                                // Set PORTA as 0
11  ADC_Init();                                // Initialize ADC
12  delay_ms(100);                             // Pause of 100ms for ADC module stabilization
13
14  //Initial read ADC and display PPM value on LCD
15  readSensor();                              // Read sensor
16  calculatePPM();                            // Calculating PPM value
17
18  FloatToStr(ppm,&txt);                      // Conversion float ppm to string txt
19  LCD_Out(2,14,"ppm");                       // Print text on LCD
20  LCD_Out(2,1,txt);                          // Print txt value on LCD
21
22  while(1) {
23
24    delay_ms(500);                           // Pause 500ms
25    readSensor();                            // Read sensor
26    calculatePPM();                          // Calculating PPM value
27    FloatToStr(ppm,&txt);                    // Conversion float ppm to string txt
28    LCD_Out(2,1,"             ");
29    LCD_Out(2,1,txt);                        // Print txt value on LCD
30
31  }
32 }