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 mV/°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  Comparator outputs high when 901 mV is exceeded Rising temperature triggers the voltage comparator

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 A request(green signal) was sent to the ultrasonic sensor for an object's distance (yellow signal)  Trigger signal width: 10 uS  Echo signal width (uS) ∝ distance (cm)  Distance (cm) = Signal width (uS) / 58  Verification  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: ,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 = ( k/910) = 37 [V/V] Microphone circuitry with signal amplifier attached

MICROPHONE (RESULTS) Sample tapping sound before amplificationSample 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) Measured frequency response of the voice filter  Verification  Measured 3dB lower cut-off: 560 Hz  Falls within 517 Hz ± 200 Hz  Measured 3dB upper cut-off: 1.48 KHz  Falls within 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?