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HOT CAR BABY DETECTOR Group #20 Luis Pabon, Jian Gao ECE 445 Dec. 8, 2014 INTRODUCTION Function of device: to detect a forgotten baby in a hot car Detection methods: Motion detection: Ultrasonic sensor Sound detection: Microphone with human voice-filter Breath detection: Carbon dioxide sensor How does it works? Temperature sensor wakes up the device Any one of the detection sensors can trigger the buzzer alarm FEATURES Compact size (4 x 3.2 in) Easy installation, independent of car seat Battery powered (4 x AA battery) Loud buzzer with warning and alarm modes Comprehensive life detection sensors Power savings mode with x14 reduction in power consumption Completed PCB with all sensors attached TOP LEVEL BLOCK DIAGRAM MICROCONTROLLER Model: PIC24FV16KA301 16-bits eXtreme Low Power PIC Main microcontroller features used in this project: 12-bits analog-to-digital converter 2 ports used for external interrupts 16-bits timers used for periodic interrupts Internal oscillator, clocked at 8MHz MICROCONTROLLER (SOFTWARE) TEMPERATURE SENSOR • Model: TI LM62 • Detection range: • 0°C to 90°C • Linear scale output voltage: • 480mV + 15.6mV/°C • Reference temperature to trigger the device: • 27°C (901mV) Temperature sensor circuitry with voltage comparator on the right TEMPERATURE SENSOR (RESULTS) Green: Temperature comparator output Yellow: Current temperature voltage Verification Rising temperature triggers the voltage comparator Comparator outputs high when 901 mV is exceeded ULTRASONIC MOTION SENSOR Model: HC - SR04 Distance Detection: 2cm - 400cm Detection Angle: 15° Advantages: Unaffected by changing temperature (compared to PIR sensor) Unaffected by outside motions (compared to Micro-wave sensor) Disadvantages: Narrow detection angle Unreliable with non-smooth surfaces Motion sensor circuitry ULTRASONIC MOTION SENSOR - CONTINUED Trigger signal width: 10 uS Echo signal width (uS) ∝ distance (cm) Distance (cm) = Signal width (uS) / 58 Verification A request(green signal) was sent to the ultrasonic sensor for an object's distance (yellow signal) A 1100 uS pulse width was measured when obstacle placed 20 cm away CARBON DIOXIDE SENSOR Onboard heating circuit for CO2 sensing Current consumption: 200 mA CO2 detection range: 400 - 10,000 ppm CO2 sensor circuitry CARBON DIOXIDE SENSOR (RESULTS) Increasing CO2 concentration (decreasing output voltage) Decreasing CO2 concentration (increasing output voltage) MICROPHONE Microphone Specs: Electret Condenser Microphone Sensitivity -47 ± 3 dB Operating frequency 100 to 20,000 Hz Signal to noise S/N 56 dBA Max current 0.2 mA Signal Amplifier Specs: R16 = 910 Ohm R1 = 33 kOhm Amplifier Gain = (1 + 33 k/910) = 37 [V/V] Microphone circuitry with signal amplifier attached MICROPHONE (RESULTS) Sample tapping sound before amplification Sample tapping sound after amplification ANALOG VOICE FILTER 2 stage, 4th order Chebyshev band-pass filter (Designed 3dB pass band: 517Hz ~ 1.358kHz) ANALOG VOICE FILTER (RESULT) Verification Measured 3dB lower cut-off: 560 Hz Falls Measured 3dB upper cut-off: 1.48 KHz Falls Measured frequency response of the voice filter within 517 Hz ± 200 Hz within 1.358 KHz ± 200 Hz Measured passband ripples < 1dB DETECTION ALGORITHMS FOR THE SENSORS • Ultrasonic motion sensor: • Create a restricted zone (25cm from the sensor during demo). Triggers the alarm if it detects an object within the restricted zone • Carbon Dioxide Sensor: • Sample the CO2 concentration once per second. If CO2 concentration is rising 5 seconds in a row, trigger the alarm. • Voice Sensor: • Use amplitude detection: trigger alarm if the measured voice voltage is 5% above or below the center voltage RECOMMENDATIONS FOR FURTHER WORK Hardware: Use a more energy efficient CO2 sensor Add a wireless module for offsite alert interface the alarm to the car's horn implement a low battery indication circuit Implement a reverse battery protection circuit Software: Implement a more advanced DSP algorithm to only detect a baby's voice Implement an algorithm to detect movement, regardless of the distance from the sensor CONCLUSION The functionality of the baby detector device was fully demonstrated Lessons learned: Conduct more circuit simulations before making the first PCB PCB prototype should be easy to test: i.e. bigger board size, more test points Realize our low power microcontroller cannot handle advanced signal processing technique for the audio QUESTIONS?