4. Input: Amplification & Filter
● In order to perform digital operations an analog signal must be converted into corresponding
digital output using Analog to Digital Converter (ADC).
● However, the noise outside of the band of interest makes the digital conversion a problem
due to unwanted added component
● Moreover, the low input signal (voice) must be amplified
● Design: An input amplifier with Filter topology is used to clean up incoming voice signal and
prepare it for processing.
5. Input System Design:
● In this project, the audio signal recorded by microphone is used for
amplification and filtering.
● Sound signal is within 0-20 kHz. A filter of 20kHz cutoff frequency is designed.
6. Input Circuit:
● System must perform two functions:
○ DC Shift of 2.5V: A non-inverting amplification
○ 40dB amplification with 20kHz cut-off frequency: A inverting amplification with RC
based filter at feedback of the amplifier.
14. SD Library
●SD library reads the data from the SD card, and write
to the SD card.
●SPI library is needed to communicate the arduino with
the shield.
●The data is written as a wav file where every block
contains some number of bits.
16. DAC
●Digital signals coming from arduino will be converted
into analog signal.
●A Buffer amplifier to protect the signal.
●Low pass filter to reduce the noise.
●Huge capacitor for better quality sound.
17. DAC vs PWM
●DAC will not give space to obtain the data from the SD
card.
●PWM is the solution to get enough space for the SD
card to do its functionality.
22. WHY LM386 ?
1) Quiescent power architecture which allows the unit to consume very little power (about 24mW)
when the device speaker is not in use
2) Easy gain control through the change of a single external capacitor
3) Cheaper, smaller and more effective option compared discreetly driven transistor based circuits
that require more components
4) Built-in large input resistance to prevent over current flow
