A hardware-based Carbon Monoxide (CO) monitoring system developed as a group project for the CSE 122 – Electrical Circuits course (Fall 2025).
The system uses an ESP32 Dev Module and an MQ-7 gas sensor to measure CO concentration continuously over a 7-day period, applying circuit and embedded system concepts such as PWM control, MOSFET switching, and sensor calibration.
- Course Code: CSE 122
- Course Title: Electrical Circuits
- Semester: Fall 2025
- Project Type: Group Project
- Contributors: Name1, Name2
This project implements a real-time CO concentration monitoring system using the MQ-7 gas sensor interfaced with an ESP32 microcontroller.
The MQ-7 sensor requires a specific heater cycling profile to operate accurately. To achieve this, an N-channel logic-level MOSFET (IRLZ44N) is driven using ESP32 hardware PWM (LEDC) to dynamically control the heater voltage.
The system performs:
- A 60-second high-heating phase (5V) for sensor cleaning
- A 90-second low-heating phase (~1.4V) for stable sensing
- Continuous CO data acquisition and logging via the Serial Monitor
This project emphasizes electrical circuit design, power control, and embedded system integration.
- Design a functional CO monitoring system using discrete circuit components
- Implement MQ-7 sensor heater control using PWM and MOSFET switching
- Apply electrical circuit concepts such as voltage control and load regulation
- Collect and analyze CO concentration data over an extended duration
- Practice embedded systems programming with real sensor data
- ESP32 Dev Module – Main microcontroller and data processing unit
- MQ-7 Gas Sensor – Carbon monoxide detection
- IRLZ44N N-Channel Logic MOSFET – PWM-based heater voltage control
- Resistors – Load resistance and signal conditioning
- USB Power Supply – Power source for the system
The MQ-7 sensor heater requires alternating heating voltages to function correctly.
In this design:
- The ESP32 generates PWM signals using its hardware LEDC module
- The IRLZ44N MOSFET acts as a low-side switch to control heater power
- Duty cycle modulation is used to achieve an effective heater voltage of ~1.4V
- The sensor’s analog output is connected to an ESP32 ADC pin with proper attenuation
This approach allows precise control of heater behavior while maintaining circuit simplicity.
- The MQ-7 heater is powered at 5V for 60 seconds to remove adsorbed gases
- Heater voltage is reduced to ~1.4V for 90 seconds using PWM control
- The sensor output voltage is read via ESP32 ADC
- Sensor resistance (Rs) is calculated and converted to CO concentration (PPM)
- Data is continuously logged to the Serial Monitor
This cycle repeats continuously during operation.
- MOSFET Type: IRLZ44N (N-channel, logic-level)
- PWM Source: ESP32 hardware PWM (LEDC)
- PWM Frequency: 1 kHz
- PWM Resolution: 8-bit
- Duty Cycle:
- 100% (5V) for high-heat phase
- 28% (~1.4V average) for low-heat phase
PWM is used strictly for voltage control, not signal modulation.
The MQ-7 sensor requires a defined preheating cycle:
- 60 seconds at 5V (high-heat phase)
- 90 seconds at ~1.4V (low-heat phase)
Calibration is performed by determining the sensor resistance (R₀) in clean air.
This calibrated value is then used to estimate CO concentration based on the sensor’s characteristic curve.
- Sampling Interval: Every 10 seconds
- ADC Samples: Averaged over multiple readings
- Data Output: Serial Monitor
- Monitoring Duration: 7 days continuous operation
Although the system implements the recommended MQ-7 heater cycling profile and basic calibration using a reference resistance (R₀) in clean air, the collected CO concentration data should be considered indicative rather than laboratory-grade.
Due to time and equipment constraints, a full multi-point calibration using certified CO gas concentrations was not performed. As a result:
- Absolute CO concentration values may deviate from true environmental levels
- Sensor drift and environmental factors (temperature, humidity) may affect accuracy
- The system is more suitable for trend observation and relative comparison than precise measurement
Improving calibration accuracy would require controlled gas exposure, long-term stabilization, and cross-validation with a reference-grade CO sensor. These enhancements were beyond the scope of this course project but are identified as important future improvements.
- Development Platform: Arduino IDE
- Programming Language: C++
- Microcontroller Framework: Arduino core for ESP32
- Libraries Used:
- Standard Arduino libraries
<math.h>for logarithmic and power calculations
The firmware handles heater timing, PWM control, ADC sampling, calibration logic, and data logging.
CSE122-ElectRICAL-CIRCUIT-PROJECT/
│
├── first_ESP32_project/
│ └── first_ESP32_project.ino
│
├── ProjectReport.pdf
│
└── README.md
│
└── ImplementedCircuitDiagram.png
│
└── PracticalCircuit1.jpg
│
└── PracticalCircuit2.jpg
A detailed formal project report was prepared as a mandatory requirement for CSE 122.
The report includes:
- Theoretical background
- Circuit analysis
- Experimental setup
- Data analysis and discussion
This project is released under the MIT License.
- This repository focuses on system-level understanding and implementation
- Detailed derivations and experimental analysis are intentionally kept in the project report
- The project reflects both academic learning outcomes and practical embedded systems experience
✔ Completed
✔ Tested
✔ Documented