Embedded systemsDecember 2024 - April 2025

Air Quality Monitoring Device

IoT Environmental Sensing with Solar Power Integration

Solar Powered
Rechargeable battery with solar charging
Multi-Sensor
PM2.5, CO2, temperature, humidity integration
Wireless Display
Readings sent to a portable LCD and warning LEDs

System Overview

Two ESP32 units connect environmental sensing to a portable LCD and PM2.5 indicator LEDs.

The sensor measures particulate matter, CO2, temperature, and humidity using rechargeable power with solar charging. The presentation records lab comparisons and power tests, alongside unstable readings, limited wireless range, and weather-constrained solar evaluation.

How it actually works

From sensor bytes to a warning light

Follow one reading through the airlink firmware, from the particulate sensor's serial frame to the monitor's LEDs and a laptop log, then compare it with the team's lab and campus measurements.

Things to try

In Show and warn, drag PM2.5 to exactly 35 and watch the LEDs keep their colour.
In Read CO2, move the voltage drop and see how fast the reading climbs.
In Field data, open Campus PM2.5 and switch between Outside HM lab and KMITL dorm.

Built from the project's own code and documents.from code: A constant or rule copied from the project's repositoryfrom report: A value from the project's report or presentationsimulated: Computed in your browser by running the project's logic

The particulate sensor streams a frame over a software serial port on GPIO 21 at 9600 baud. The firmware checks the two header bytes and assembles each value from a high and a low byte. from code: main.cpp L8 and L108

PM2.5 the sensor reports19 µg/m³

Your input. It is split into the two bytes the sensor would send.

index

byte 12, 13

00 13

pm2_5

Bytes marked ·· are other fields of the frame the figure does not fill in. The loop stops after index 15 and drains the rest of the buffer.

Air Sensor/src/main.cpp · ReadPMS3003()View on GitHub

void ReadPMS3003(void)
{
int index = 0;
char value;
char previousValue;
while (mySerial.available())
{
value = mySerial.read();
if ((index == 0 && value != 0x42) || (index == 1 && value != 0x4d))
{
Serial.println("Cannot find the data header.");
break;
}
if (index == 10 || index == 12 || index == 14)
{
previousValue = value;
}
else if (index == 11)
{
pm_readings.pm1 = 256 * previousValue + value;
Serial.print("{ ");
Serial.print("\"pm1\": ");
Serial.print(pm_readings.pm1);
Serial.print(" ug/m3");
Serial.print(", ");
}
else if (index == 13)
{
pm_readings.pm2_5 = 256 * previousValue + value;
Serial.print("\"pm2_5\": ");
Serial.print(pm_readings.pm2_5);
Serial.print(" ug/m3");
Serial.print(", ");
}
else if (index == 15)
{
pm_readings.pm10 = 256 * previousValue + value;
Serial.print("\"pm10\": ");
Serial.print(pm_readings.pm10);
Serial.print(" ug/m3");
}
else if (index > 15)
{
break;
}
index++;
}
while (mySerial.available())
mySerial.read();
Serial.println(" }");
}

Air sensor circuit schematic: PMS5003, MG811 and DHT22 wired to an ESP32 devkit, with five 5 V solar panels in parallel feeding a solar charger and a 3.7 V battery — Sensor circuit: PMS5003 on D21/D22, MG811 on D33, DHT22 on D32.Slides p. 14

Pins, rules and constants are copied from the airlink firmware at a pinned commit, and the LED, label, arc and CO2 maths run in your browser with your inputs. Measurements come from the team's slides: the battery tables are exact, while the sensor traces were read off the published charts and are approximate. The repository README names a PMS3003 and TGS4161; the slides and schematic name a PMS5003 and MG811.

How it works

Measure air conditions where people are working.

1
Sample environmental conditions
The sensor ESP32 collects readings from the particulate, CO2, temperature, and humidity sensors housed in the ventilated sensing unit.
2
Transmit readings wirelessly
Send the sensor data to the receiver ESP32, with the system also supporting viewing readings on a connected computer.
3
Display local air-quality information
Present readings on the receiver's LCD and control its indicator LEDs according to the measured PM2.5 level.

Project Demo

The project's own demonstration footage.

Air Quality Monitoring Device video preview

Watch Air Quality Monitoring Device on YouTube

Engineering features

Built a two-unit air quality monitor on ESP32s, with a solar-charged sensing box and a portable receiver linked wirelessly.
Integrated PM2.5, CO2, temperature, and humidity sensors into a single monitoring device and transmitted readings to a receiver unit, with optional laptop monitoring.
Built a portable receiver with an LCD and LEDs whose colour follows PM2.5 thresholds set in the firmware.
Ran lab and campus tests against a purifier's readings and measured charging and battery runtime, documenting the sensor offset and range limits.

Inside the build

The control logic, integration and design decisions, one note at a time.

Separate sensing and display hardware

The system uses two ESP32 boards, a PMS5003 particulate sensor, an MG811 CO2 sensor, and a DHT22 temperature/humidity sensor. The receiver combines an LCD with an LED strip, allowing the sensing hardware and the user-facing display to occupy different locations.

Solar charging evaluated alongside load

Parallel solar panels feed the sensor charging system, and a rechargeable battery supplies the electronics through power conversion hardware. The presentation distinguishes component-based power calculations from measured charging and discharge tables. Solar output is shown with and without load, and cloudy-weather testing constrains the charging evidence.

Housing for airflow and monitoring

The sensor enclosure uses louvers for ventilation and a roof overhang intended to reduce direct rain entry. A separate solar box houses the charging arrangement. The receiver enclosure provides access to the screen and indicator lights, keeping the sensing, charging, and monitoring functions in distinct physical units.

Build artifacts

Figures taken from the project's own report or presentation.

Reported PM2.5 readings over time compared with the purifier's minimum and maximum reference readings — HM lab PM2.5 comparison chart extracted from PDF page 26; it shows the reported sensor offset from purifier readings.

Evidence & limitations

What the project documents show, and where each claim comes from.

Lab comparisons and campus measurements

The presentation plots PM2.5 and CO2 readings in the HM lab and at campus locations. The PM2.5 lab comparison shows a positive offset from the purifier's readings; outdoor plots were taken at different times of day, so they do not establish a simultaneous location comparison.

Power and communication results

Charging and discharge tables document USB charging, solar charging, and battery operation. The conclusion reports data transfer between two ESP32 boards and a PC, plus display and LED operation, while acknowledging transmission-range and solar-testing problems.

Air monitor project presentation
PDF pages 6-18: objectives, design, and power calculations; 20-29: tests; 30-31, 34: limitations and conclusion.
Airlink source repository
Project demonstration
Linked in the presentation and supplied portfolio.

CAD & mechanical models

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Air Monitoring Housing

STL

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Air Sensing Housing

STL

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Solar Charger

STL

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Project Resources

The original documents behind this case study.

Presentation Slides
PDF file
View Download
3D CAD files
ZIP file
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Air Quality Monitoring Device

Solar Powered

Multi-Sensor

Wireless Display

System Overview

From sensor bytes to a warning light

How it works

Sample environmental conditions

Transmit readings wirelessly

Display local air-quality information

Project Demo

Engineering features

Inside the build

Separate sensing and display hardware

Solar charging evaluated alongside load

Housing for airflow and monitoring

Build artifacts

Evidence & limitations

Lab comparisons and campus measurements

Power and communication results

CAD & mechanical models

Air Monitoring Housing

Air Sensing Housing

Solar Charger

Project Resources

Hiring for robotics or embedded work?