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TEL412 Exam ProjectDesign of sensor for detecting
rodents
Kονταδάκης-ΝτίληςΗΜΜΥ Πολυτεχνείου Κρήτης, Ιανουάριος 2011
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Outline
• Problem: Rodents infesting crops• Rodent Alert with Sensor design– Microphone sensor
• Testing• Future work• Other applications• References
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Rodents infesting crops
• by 1974, rodents responsible for annualloss of 33 million tonesof stored cereals and rice
• Rodents may carry andtransfer diseases
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Rodents infesting crops
• Recent Rising Example: Snail farming– Mice are a threat to snail farming
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Microphone sensor
• Rodents make high frequencies sounds– Example: Rat squeak at 2.5 - 5 kHz– Easily distinguishable from human voice(<1 kHz)– and common environmental noises(<1.5 kHz)
• Result: cut low frequencies(<2 kHz)• Sampling frequency at least 10 kHz
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Microphone sensor• Components:– Microphone– Low Voltage Audio Power Amplifier(LM386)– Microcontroller unit(C8051F320)
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Microphone sensor
• Processing signal in MCU• Find basic frequency of sound• FFT not suitable– Main problem: needs memory– C8051F320 has 256 bytes of data memory most of
which are reserved
• We need real time processing. How?
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Microphone sensor(Zero Crossing)
• Zero Crossing Implementation– ADC sampling frequency: fs = 10 kHz
– Take window of 30 ms => (0.03*10000) samples =300 samples
– Separate data to training and testing • 100 samples training(10 ms)• 200 samples testing(20 ms)
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Microphone sensor(Zero Crossing)• Training(100 samples)– Find Threshold(mean on samples)
• Testing(200 samples)– Check how many times signal crosses threshold– Then f0=(times*fs)/(2*samples) Hz
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Microphone sensor(Zero Crossing)
• Summary– Faster than fft(O(n) instead of O(nlogn))
– Finds only basic frequency of sound
– Not good for very low frequencies(<100 Hz)
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Future work
• Problem with circuit– Voltage drops slowly after sound detection– Smaller accuracy on measurements
» Example: when fs = 10 kHz(demo) , cannot detect sound frequencies around 1.5 kHz
• Send detection result to base station(e.g. farmer)
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Other applications
• Besides rodent detection:– Sensor could detect certain insects• Higher frequency sounds• Change sampling frequency
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