Low power device sensor module - Sound Sensor Module First Revision



Sound Sensor Module (First Revision)



Figure above shows Full Schematic of Sound Sensor Module (First Revision) 1) Input Sensor 2) Inverting Amplifier 3) High Pass Filter 4) Low Pass Filter


Figure above shows the schematic of sound sensor module (first revision). It is divided into four main parts. The first part which is figure 1) is input sensor which utilizes electret microphone. Considering the input sound is from living thing (human and pet), hence the allowable frequency must be between 300Hz to 3 kHz which is a frequency of human voice. The voltage generate by this passive electret microphone is very small which is lower than 100mV and usually 20 to 30mV. The signal generated will have both dc and ac component inside. It will go through the capacitor in order to filter out the dc component from the signal. The signal after this part will be call as raw signal.


The second part which is figure 2) is inverting amplifier. At this stage, the raw signal will be amplified to the gain of 10. By using the equation (2) with 100k value of Rf and 10k value of Ri, the output signal with gain of 10 can be generated with offset of 2.5V. This offset is due to the 2.5V reference at positive input of the op-amp. This reference is needed in order to amplify both positive region and negative region of the raw signal. The signal after this part will be called as invert gain signal.

The third part which is figure 3) is high pass filter. At this stage, the invert gain signal will be filter with cut-off frequency of 300 Hz and only allow signal above 300Hz to pass through it. By using equation (1) with 5k value of R and 0.1u value of C, the cut-off frequency of 300 Hz can be made. Then it will once again go through another amplifier in order to revert again the signal to its non-inverting value. The signal after this part will be called as low pass non-inverting signal.

The forth part which is figure 4) is low pass filter. At this stage, the low pass non-inverting signal will be filter with cut-off frequency of 3 kHz and only allow signal below 3 kHz to pass through it. By using equation (1) with 500 value of R and 0.1u value of C, the cut-off frequency of 3 kHz can be made. The signal after this part can now be used by the controller to be processed.

However, this “old school” circuit will not be used. This is because the number of component use is large which bring increase of cost and power use for mass manufacturing.

Circuit Gallery
 Circuit above contain filter and amplify

 Circuit above contain input circuit, amplify, sine wave generation (use as test signal) and power regulator

 Circuit above contain input circuit, amplify, filter, and power regulator. Compact version.

Circuit above contain input circuit, amplify, and filter. Compact version.

Analysis Gallery - Picture

Testing the sine wave generation use as test signal

Testing the functionality of the circuit

Analysis Gallery - Video

Sound Module testing - input directly from microphone


Sound Module - Input from microphone and after filtering

Sound Module - Input after filtering going through fourier transform


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