HOT CAR BABY DETECTOR Group 20 Luis Pabon

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 x 14 reduction in power consumption Completed PCB with all sensors attached

TOP LEVEL BLOCK DIAGRAM

MICROCONTROLLER Model: PIC 24 FV 16 KA 301 16 -bits e. Xtreme 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 8 MHz

MICROCONTROLLER (SOFTWARE)

TEMPERATURE SENSOR • Model: TI LM 62 • Detection range: • 0°C to 90°C • Linear scale output voltage: • 480 m. V + 15. 6 m. V/°C • Reference temperature to trigger the device: • 27°C (901 m. V) 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 m. V is exceeded 901

ULTRASONIC MOTION SENSOR Model: HC - SR 04 Distance Detection: 2 cm - 400 cm 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 u. S Echo signal width (u. S) ∝ distance (cm) Distance (cm) = Signal width (u. S) / 58 Verification A request(green signal) was sent to the ultrasonic sensor for an object's distance (yellow signal) A 1100 u. S pulse width was measured when obstacle placed 20 cm away

CARBON DIOXIDE SENSOR Onboard heating circuit for CO 2 sensing Current consumption: 200 m. A CO 2 detection range: 400 - 10, 000 ppm CO 2 sensor circuitry

CARBON DIOXIDE SENSOR (RESULTS) Increasing CO 2 concentration (decreasing output voltage) Decreasing CO 2 concentration (increasing output voltage)

MICROPHONE Microphone Specs: Electret Condenser Microphone Sensitivity -47 ± 3 d. B Operating frequency 100 to 20, 000 Hz Signal to noise S/N 56 d. BA Max current 0. 2 m. A Signal Amplifier Specs: R 16 = 910 Ohm R 1 = 33 k. Ohm 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, 4 th order Chebyshev band-pass filter (Designed 3 d. B pass band: 517 Hz ~ 1. 358 k. Hz)

ANALOG VOICE FILTER (RESULT) Verification Measured 3 d. B lower cut-off: 560 Hz Falls Measured 3 d. B 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 < 1 d. B

DETECTION ALGORITHMS FOR THE SENSORS • Ultrasonic motion sensor: • Create a restricted zone (25 cm from the sensor during demo). Triggers the alarm if it detects an object within the restricted zone • Carbon Dioxide Sensor: • Sample the CO 2 concentration once per second. If CO 2 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 CO 2 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 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?