Breathalyzer (Etilotest)
Introducere
Purpose: To provide an accessible, low-cost sobriety test tool built entirely from scratch using ATmega328P peripherals.
Starting idea: The project originated from the practical need for a simple, register-level embedded systems project that integrates multiple lab concepts into a real-world product.
Why it is useful: It demonstrates a complete embedded pipeline — analog sensing, interrupt-driven input, I²C communication, and GPIO output — while producing a functional, demonstrable device.
Descriere generală
The diagram below shows all hardware and software modules and how they interact.
- MQ-3 sensor — outputs an analog voltage proportional to alcohol concentration → read via ADC (PA0)
- Temperature sensor (optional) — provides ambient temperature for MQ-3 calibration → read via ADC (PA1)
- Buttons x2 — trigger test start and calibration → connected to INT1 (PD3) and INT2 (PB2) with software debouncing via systicks
- LEDs (green / yellow / red) — indicate safe / warning / danger status → controlled via GPIO (PC0–PC2)
- LCD/OLED display — shows measured BAC value and status text → driven via I²C (TWI)
- Buzzer (optional) — auditory alert on high readings → controlled via PWM or GPIO
- ATmega324P — central MCU coordinating all peripherals
Hardware Design
| Component | Qty | Notes |
| — | — | — |
| ATmega324P | 1 | Main MCU |
| MQ-3 alcohol sensor | 1 | Analog output |
| Temperature sensor (LM35 or NTC) | 1 | Optional, for calibration |
| Push buttons | 2 | Test start + calibration |
| LEDs (green, yellow, red) | 3 | Status indicators |
| 220Ω resistors | 3 | LED current limiting |
| LCD 16×2 or OLED 128×64 (I²C) | 1 | Display module |
| Buzzer | 1 | Optional audio alert |
| Breadboard + jumper wires | — | Prototyping |
| 5V USB power supply or battery | 1 | Power |
| 16 MHz crystal + 2×22pF caps | 1 | MCU clock |
| 10kΩ pull-up resistors | 2 | I²C lines SDA/SCL |
Pin mapping:
- MQ-3 analog output → PA0 (ADC channel 0)
- Temperature sensor → PA1 (ADC channel 1)
- Button 1 → PD3 (INT1)
- Button 2 → PB2 (INT2)
- LED green → PC0, LED yellow → PC1, LED red → PC2
- SDA → PC1 (TWI), SCL → PC0 (TWI)
- Buzzer → OC0B (PD5) or PD7
Diagram
Software Design
Third-party libraries and sources:
- No external libraries — all peripheral drivers written from scratch using registers
- Optional: lightweight I²C LCD driver adapted from course lab materials
Planned algorithms and data structures:
- ADC sampling — single-shot mode on PA0/PA1; average of 16 samples per reading for noise reduction
- MQ-3 calibration — baseline resistance R0 measured in clean air on startup; BAC estimation uses the Rs/R0 ratio from the MQ-3 datasheet characteristic curve
- Temperature compensation — Rs/R0 ratio adjusted using ambient temperature reading from PA1
- Interrupt handling (INT1/INT2) — button press sets a volatile flag inside the ISR; debounce enforced via systicks counter (Timer1 CTC, 1 ms tick); flag processed in main loop
- Display logic — BAC classified into ranges (< 0.2‰ → green, 0.2–0.5‰ → yellow, > 0.5‰ → red); value and status string sent over I²C to display
- LED/Buzzer output — GPIO write for LEDs; optional PWM tone on OC0B for buzzer alert
Rezultate Obţinute
- Clean air → 0.000 mg/L
- Inside an alcohol recipient → >0.2mg/L
Concluzii
To be completed
===== Download =====
<note warning>
* Github: https://github.com/Mihai4GH/PM_Proiect
Files will be uploaded under namespace :pm:prj2025:cc:your_name.
The archive will contain:
* src/ — all .c and .h source files
* schematics/ — KiCad or draw.io schematic files
* README.md — project description and build instructions
* Makefile — compile and flash script (avr-gcc + avrdude)
* CHANGELOG.md — version history
</note>
===== Jurnal =====
<note tip>
| Week | Activity |
|—|—|
| Week 1 | Component selection, initial schematic, MQ-3 and ATmega324P datasheet study |
| Week 2 | Hardware implementation, prototyping |
| Week 3 | Software implementation, fixing wrong read values on MQ-3 sensor |
</note>
===== Bibliografie/Resurse =====
<note>
Resurse Hardware:
* MQ-3 Datasheet – Hanwei Electronics
* ATmega324P Datasheet – Microchip Technology
* LM35 Datasheet – Texas Instruments
Resurse Software:
* AVR-GCC / AVR-libc documentation
* Microchip Studio (AVR Studio)
* Microchip AN2480 – I²C/TWI for AVR
* PM Lab materials – course wiki (laboratoare GPIO, Întreruperi, Timere, ADC, I²C)
</note>
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