SIMPLE VOICE RECORDER

Introduction

• The main objective of this project was to design and implement a voice/sound recorder capable of simple voice modulation. Hence, we have developed a simple voice recorder that can playback audio which is recorded by the user through a microphone. The user is also able to implement a low-pass filter effect to recorded audio and playback the modified sound as well. Up to 3 recordings without any effects can be saved in the device and can be selectively played back, and we have made this using the ATmega328p microcontroller and various other inexpensive electronic components. Currently we have developed the physical prototype as a breadboard implementation. Furthermore, we have been involved with the PCB and enclosure designing which will influence the production of the finished product as a commercially successful device. Problems, improvements and alternatives regarding this project were also discussed and evaluated.

• When designing the functionality of the prototype, many critical factors have to be considered. Firstly, this project is implemented using appropriate ADC and DAC with 8 bit PCM. Hence, aspects such as sampling rate, quantization and compression needed for the PCM should be evaluated when doing so. Furthermore, the storage of recorded audio tracks in an SD card is another point of importance, with the number of samples stored, the file format used for storage etc. needed to be considered as well. With regards to audio enhancement, the type of effects to be implemented are essential to be identified when developing the algorithm. Next, concerning the perspective of the user of the prototype, elements such as input device, UI and output device design should be executed. The use of an appropriate microphone module and any other required input devices, an LCD screen to act as a clean and simple UI and a speaker with an appropriate amplification setup are included in this. Thus, the aforementioned features were experimented with using various parameters and variables and weighing out the pros and cons before they were finalized for this project. Hence, this paper details the attempt to develop a working prototype (breadboard implementation) of a simple voice recorder using the ATmega 328p microcontroller alongside other affordable electronic components, in a suitable way that can be expanded for commercial use later on.

List of components used

Modules and External components

• 1 x KY-037 Microphone module • 1 x 16x2 Alphanumeric LCD Display • 1 x Micro SD Card Module • 1 x PCF8574 LCD I2C • 1 x 4x4 Keypad • 1 x TPA3118 Amplifier module • 1 x 8Ωspeaker • 1 x 10 KΩ potentiometer • 1 x 9V Battery

Main PCB

• 1 x ATmega 328p microcontroller • 1 x DAC0808 IC • 1 x LM7805CV Power regulator • 1 x 16 kHz crystal oscillator • 3 x100 nF capacitors • 2 x 22 pF capacitors • 1 x Switch • 3 x10 KΩ resistors • 1 x 330 nF capacitor • 1 x 330Ω resistor

Matlab

In this project for the effect to be induced in playback, lowpass filtering is used. For this effect, each sample is read one by one from the pre-recorded voice sample stored in the SD card,and the values corresponding to the filtered output are stored in a new file(effects file). In the playback, the effects file is opened and played. For computing the values for the filtered output, the corresponding Matlab function is found using the first-order lowpass filter transfer function. the Matlab code and the calculation for the transfer function for lowpass first-order filtering done for an audio sample in wave file. And the spectrum obtained from the Matlab. Here the audio sample is filtered using a lowpass filter with a cutoff frequency of 1000Hz. Similarly, in Matlab we had tested adding echo effects for the recorded wave file. In this, each sample of the input signal is read and an empty array is created to store the set of past sample data and then combined to give the resultant output. The Matlab code done for the echo effects shows the original and resultant spectrum after the echo effects. However, the echo effects part of our testing was not implemented in the final product due to various limitations

Low Pass Filter

Echo effect

Arduino

With the physical implementation, the waveform obtained for the low pass filtering for a random signal

ALGORITHM DEVELOPMENT

The following block diagram is shown in represents the basic functionality of a simple voice recorder. By following these basic steps, we develop the related algorithms and appropriate functions in the Arduino platform and design and simulates in proteus software.

SIMULATIONS AND INPUT-OUTPUT WAVEFORMS

The Arduino implementation is simulated through proteus professional software. The circuit design for the proteus simulation. As an audio sample here sinusoidal signal of a single frequency of 500Hz is used. Samples are taken at a rate of nearly 4000 samples per second and stored in a comma-separated value file format in the SD card.

results

SCHEMATIC AND PCB DESIGN

The PCB design for the simple voice recorder circuit was made in Altium designer software. PCB design contains three main units they are power supply unit, main microcontroller ATmega 328p, DAC IC.

PCB Design

ENCLOSURE DESIGN

In designing the enclosure we considered several factors. Convenient usability was considered when deciding the placement of buttons, display and the microphone. Unscrewing the two plates would reveal all the connections and the battery hostler for easy replacement of parts. Maintaining aesthetic look and feel complementing the functionality, was also a concern.

USER INTERFACE

For the user to interact with our product, we have included a keypad which can be used for selection of the recording option and selective playback of the different recorded files with or without effects. From the simulation stage we are developing the final product which will work as follows. When the user turns on the device first a greeting message will be shown, then the selective option will be displayed. Six selective buttons are present for recording, playing the original file, playing the filter file, and selecting the appropriate audio clip. In the simulation, we designed for our device to contain upto three recordings. If we try to go beyond three files, there will be a prompt to delete the files first. we implemented the user interface in the simulation. To start recording, the user should press the record button (number 6) and after the subsequent press of the record button, the recording will be completed. After that, to play the original file, the user should press the play button (number 4). Then they have to select the file number, whether it is one, two or three. Similarly, for the play effects, the user should press the effect button (number 5) and choose the respective audio clip number.

PHYSICAL PROTOTYPE

The following image shows the physical circuit implementation using the breadboard. Using the aforementioned theories, simulations and components mentioned in the METHOD section, we have designed this circuit in a user-friendly way to achieve effective operation.