Snorecoder with SD Logging

People often keep ignoring their habit of snoring considering it a flawless, routine activity. When medically stated, snoring is rather a vibration of respiratory structures caused due to obstructed air movement during breathing while sleeping. Sleep apnea is a sleeping disorder exemplifying abnormal pauses in breathing. These abnormalities during sleep can be checked upon using this device which we rightly call Snorecoder. It is a well – implemented project from final year engineering students of Cornell University. Snorecoder detects snoring sounds from a sleeping person and records the time and intensity of each snore. The data recorded is then stored on a SD card which can be viewed on a personal computer.

The device operates in two different modes; Trigger and Continuous. Trigger mode logs a value of maximum snore intensity and its time stamp for a single snore event and Continuous mode records the snore sounds at a rate of around 500Hz. The mode of operation can be switched by a user using 4 input push buttons.

Some of the major components of the project hardware are STK500 development board (ATmega644 microcontroller), Hosiden electret condenser microphone, Operational amplifiers, 5-3.3V Voltage Regulator, SD card and holder and a 16×2 LCD.

Typical range of snoring frequencies lies within 100-800 Hz. Following which, this system is designed accordingly. A working microphone amplifier and filter circuit is the first objective of the snorecoder. Microphone with a huge gain of 3000 is used to input the snore signals into the system followed by two low pass filters with cut-off frequency 16Hz and 60Hz respectively. The circuit has a second order voltage controlled voltage source filter with a cut-off frequency of 800Hz. The microcontroller determines and interprets these snore occurrences, updates on LCD and also writes the information on SD. The microcontroller’s SCK output is given to SD card which is predefined to run at 125 KHz at startup and 2MHz for regular writing. The SD card is run into Serial Peripheral Interface (SPI) mode.

Another major aspect of this project is its software considerations used to communicate between different hardware. The software blocks include LCD writing, user interface, digital signal processing and SD logging.