Figure Above : Electret Microphone with MAX9814 breakout board schematic
Figure above show the schematic of electret microphone with MAX9814 breakout board . This breakout board which is only using a single integrated circuit is capable to do all the function in revision one and more (some of it is automatic gain control, AGC) . This breakout board can now overcome the problem in first revision which is power consumption and number of component use . The signal after this part can now be used by the controller to be processed .
Figure above : Full Schematic of Sound Sensor Module ( Second Revision )
Figure above show the full schematic of sound sensor module ( Second Revision ) . It is now consist of full hardware design from raw audio signal , digital data , process data and lastly transmit data . The electronic part in schematic above can be divided into 4 small parts . The bottom left of the figure above is a mechanical drawing of the chassis .
Figure above : Block of Sound Sensor Module ( Second Revision ) a ) battery and power block b ) sensor block c ) controller and indicator block d ) low power wireless device block
Figure above : Single Cell Lithium Polymer (Lipo) Battery
Figure a ) shows battery and power block of sound sensor module . Overall system is based on 5V system hence a battery that has more voltage from 5V is need . In this case , two lipo 3 . 7V as shown in figure above will be used which will be total up to be 7 . 4V . This 7 . 4V will go through TPS76650D low voltage dropout regulator which will be regulated to 5V . This TPS76650D has maximum quiescent current of 50uA which only contribute only small power to regulate the voltage compare to the normal 7805 series which has 8mA of quiescent current .
Figure c ) shows a controller and indicator block . In this block , there will be a controller to process the data receives from sensor block . The microcontroller use is Atmega328P which is based on 8 bit processing . The sleep function in this controller will be utilizes in order to save the power as much as possible . The controller will only wake up and use power to process the data only when it receives wake up signal generated from the op - amp which is connected to the sensor block . The op-amp use in this project also utilizes low power op-amp which is LMV358 . Other than that, this block also contain voltage indicator on order to notify the action module when the voltage of the battery is low .
Figure above : NRF24L01 Low Power RF Module
Figure d ) shows a low power wireless device block which utilizes low power radio frequency chip NRF24L01 as shown in figure above . The sleep function in this chip will be utilizes in order to save the power as much as possible . The chip will only wake up and use power to transmit the data only when it receives wake up command from the controller .
Figure Actual Design for Sound Sensor Module a ) Top layer b ) bottom layer
Figure shows PCB design for sound sensor module and actual design for sound sensor module . This board is two layer board constructions . It has the size of 5 cm times 5 cm.