Gas sensor (MQ-135) support In PSLab Android application

Along with lots of sensors provided in the PSLab Android application, recently support for a new sensor – MQ-135 gas sensor has been added to the app. In this blog, I will discuss what is this gas sensor and how to use it with PSLab Android application

MQ-135 Gas sensor

The MQ-135 gas sensors are used in air quality control equipment and are suitable for detecting or measuring of NH3, NOx, Alcohol, Benzene, Smoke, CO2. 

The Pin layout of MQ-135 sensor

(Figure 1: MQ-135 pin layout)

How to Connect MQ-135 to PSLab Board

The following diagram shows how a user can connect MQ-135 sensor to a PSLab Board. 

(Figure 2: MQ-135 and PSLab connections)

As can be seen in the diagram above connect Voltage pin of MQ-135 sensor to one of the VDD pins on the PSLab board. Connect the Ground pin of MQ-135 sensor to one of GND pins on the PSLab board. And connect Analog Output pin to CH1 pin on the PSLab board. Once these connections are made user can connect PSLab board to their mobile phone and start reading data using Gas Sensor instrument in PSLab Android application

Gas Sensor Instrument in PSLab Android Application

To provide users an interface to read values collected by MQ-135 sensor connected to PSLAb board, a new instrument screen has been added to the PSLab Android application. The UI of the screen is shown below,

(Figure 3: Gas Sensor instrument UI)

As can be seen, the user is provided with a circular meter, a text box and a graph, all of which indicates the amount of different gases sensed by MQ-135 in PPM (parts per million) unit. The data is collected by very simple lines of codes. Since we are connecting Analog Output of MQ-135 to CH1 on PSLab board, we need to read the voltage at CH1 pin. Which would be in the range of 0 – input voltage (which is 3.3V in our case). To convert the voltage values to PPM, we map these output voltages to a range of 0 – 1024. This is done by following lines of code.

double volt = scienceLab.getVoltage("CH1", 1);
double ppmValue = (volt / 3.3) * 1024.0;

As provided in all the other instruments in PSLab Android application, Gas Sensor also has data logging and importing feature. User can record the data and store it as a CSV file and import previously recorded data into the PSLab application easily.

So in conclusion, now users can utilize and experiment with MQ-135 sensor effortlessly using PSLab Android application.

A working demo of this feature can be seen in the following video

https://drive.google.com/file/d/1-KxOaqE_Y5EYquMkebYpBOEc0d7GAdLS/view?usp=sharing

References:

Tags: PSLab, Android, GSoC 19, Sensors, Gas Sensor, MQ-135

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