S15: MP3 Player with Graphic Equalizer Display

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Grading Criteria

  • How well is Software & Hardware Design described?
  • How well can this report be used to reproduce this project?
  • Code Quality
  • Overall Report Quality:
    • Software Block Diagrams
    • Hardware Block Diagrams
      Schematic Quality
    • Quality of technical challenges and solutions adopted.

Abstract

The SJ One Board, which contains an LPC1758 microcontroller, will play MP3 audio files from an SD card and display the audio frequencies on a graphic equalizer simulated by LED's, an MP3 audio decoder integrated circuit (VS1053), and equalizer analyzing IC (MSGQE7).

Introduction

An equalizer is a set of electronic filters that can adjust the frequency response of a sound system. A common type of equalizer is the graphic equalizer, which represents filter levels usually with light-emitting diodes (LED's). Depending on the integrated circuit used, a graphic equalizer shows the direct-current representation of a varying range of audio frequency bands. For instance, the MSGEQ7 CMOS IC splits audio in seven bands: 63Hz, 160Hz, 400Hz, 1kHz, 2.5kHz, 6.25kHz, and 16kHz. Commonly seen on audio devices and media software like Windows Media Player or VLC Media Player are simulated versions of audio spectra.

Objectives

Interface the MP3/Audio Decoder IC with Our Microcontroller

The first objective was to interface the MP3/Audio decoder IC (VS1053) with SJSU One board (LPC1758) using SPI bus with some additional pins for data transmit and reset purpose.

Design Software for the MP3 Player

The second objective was to design software for the MP3 player to read files from a SD card then transmit data to the MP3/Audio decoder IC to play and output sound.

Control the MP3 Player Using a remote control

The third objective was to read IR signal from a remote control using IR receiver on SJSU One board and make change on the MP3 player accordingly. Basic commands: play, pause, fastforward, rewind.

Construct Equalizer Analyzing Circuit

The fourth objective was to design the equalizer analyzing circuit using a MSGQE7 chip. The SJSU One board gives the RESET and STROBE signal to the MSGQE7. A 3.5mm audio jack was used to input the audio into the MSGQE7.

Team Members & Responsibilities

  • Thinh Lu
    • Writing VS1053 audio decoder driver
    • Designing the MP3/Audio player
  • Brian Nguyen
    • Designing the equalizer analyzing circuit
  • Andrew Pang
    • Interfacing LED matrix with SJSU One board
    • Editor-in-chief of project report

Schedule

This is our original plan and the status of each task.

Week# Ending date Task Actual
1 4/18 Order all hardware Completed.
2 4/25 Interface LED matrix with LP1758.

Play a single MP3/Audio file

Completed
3 5/1 Finish MP3 driver. Completed
4 5/15 Finish MP3 player.

Interface with a remote control.

Completed.

Not completed.

5 5/22 Interface LED's as graphic equalizer. Presenting on 5/25. Completed.

Parts List & Cost

Give a simple list of the cost of your project broken down by components. Do not write long stories here.

  • (1) LED Matrix: $24.95
  • (1) 12 V power supply: $11.59
  • (1) 5/3.3 V power supply: $4.55
  • (1) Mikro VS1053 breakout board: $21.90
  • (20) jumper wires: $1.95
  • (1) 4-pin Molex connector: $0.95
  • (1) Electric tape roll: $0.95
  • (2) Graphic equalizer display filter MSGEQ7: $4.95
  • (1) Audio Jack 3.5mm: $0.95
  • Breadboard, resistors, capacitors, all spare parts from previous CMPE courses

Total cost: $72.74

Design & Implementation

In this section, we will go over our hardware and software designs including sub-sections describing our design and implementation.

Hardware Design

Figure 1. Schematic of the Hardware Design of the MP3 Player

For the Mp3 Player, we use SPI interface to control and send/receive data from the decoder, VS1053.

As shown in Figure 1, this design uses four GPIO pins of the LPC1758 CPU including one for input and three for output. Pin 1.22 is used as output to control CS pin of the audio decoder. Pin 1.28 is used as output to control RESET pin of the audio decoder. Pin 1.19 is used as input to check the DREQ signal from the audio decoder. And pin 1.30 is used as output to control the DCS pin of the audio decoder. The audio decode shares SPI bus, SSP1, with the Micro SD.

Briefly, the pin functionality of the audio decoder can be described as follows:

  • CS is chip select pin for SCI operation (to set up and control the audio decoder),
  • DCS is a chip select for SDI operation (to play songs),
  • RESET is to perform a hard reset on the audio decoder,
  • and DREQ is used to notify when the decoder can receive more data (busy = 0, ready = 1).

The rest, SO, SI, and SCK, follow the SPI protocol, as explained in LPC 1758 and VS1053 datasheets.

Figure 2. The schematic of the equalizer circuit

The two main components of the equalizer circuit were the audio jack and MSGEQ7 chip. The audio jack divides the audio into two audio channel, left and right. The left and right audio each go into the audio input of two seperate MSGEQ7. The MSGEQ7 is an audio spectrum analyzer chip with seven band-pass filters from 63 Hz to 16,000 Hz. Two MSGEQ7 chips were used to drive 2x5 LEDs. The MSGEQ7 is controlled with two digital signals, RESET and STROBE. A positive RESET signal is needed in order to start operation. The values of each of the bands can be read whenever seven negative pulses are inputted into STROBE. The values of the seven bands are analog values that are fed into an analog-to-digital converter (ADC) of two LPC1768. The ADC provides an us with a value between 0-4096 since the ADC resolution is 12-bit. The values from the ADC were divided by 40.96 in order to produce a value between 0 and 100. This new value is used in the pulse-width modulation in order to control the brightness of the 2x5 LEDs.

Figure 3. Schematic of proposed LPC1758/LED matrix interface.

Initially, we planned on outputting the audio frequency spectrum on a 16-by-32 LED matrix, with connections shown in Figure 3 in which two LPC1758's would be connected by UART, then the LPC1758 interfaced with the matrix via GPIO connections. However, we could not implement this part and decided on an alternative design (see Problem #1 section below).

Hardware Interface

For the Mp3 player, we use SPI bus to communicate between the LPC1758, micro SD card, and VS1053. For the audio decoder, it has two operation modes, SCI and SDI. SCI is for control settings of the decoding process (volume, bass/treble value, clock speed, decoding/recording). And SDI is for receiving data; for example, when we want to play a song, we simply read the song from the SD card then send to the decoder, which is set up properly; the decoder will then just decode the data from the audio file and output sound to speaker/headphone. For driver, we break it down into small functions to set up the connection interface between the CPU and the audio decoder, to set up the audio decoder by sending the value to its control registers, to send a single byte as well as 32 bytes of data to the decoder to play songs.

Hardware Interface Driver
   LPC_GPIO1->FIODIR |= (1<<22);   //set pin P1.22 as output -- CS signal
   LPC_GPIO1->FIODIR |= (1<<28);   //set pin P1.28 as output -- RESET signal
   LPC_GPIO1->FIODIR |= (1<<30);   //set pin P1.30 as output -- DCS signal

   LPC_GPIO1->FIODIR &= ~(1<<19);  //set pin P1.19 as input -- DREQ signal

   LPC_GPIO1->FIOSET = (1<<28);    //set pin P1.28 high initially
   LPC_GPIO1->FIOSET = (1<<30);    //set pin P1.30 high initially
   LPC_GPIO1->FIOSET = (1<<22);    //set pin P1.30 high initially

   ssp1_init(); //initialize ssp1

Software Design

LED Matrix

For interfacing the SJ One board with LED matrix, we intended to have the program activate a select number of LED's of a certain color, depending on audio frequencies read by the MSGEQ7 IC.

Pseudocode is as follows: 

#define CLOCKPIN 0 // P0.0
#define LATCHPIN 29 // P0.29
#define OEPIN 1 // P0.1
#define APIN 20 // P1.20
#define BPIN 19 // P1.19
#define CPIN 30 // P0.30
#define R1PIN 0 // P2.0
#define R2PIN 1 // P2.1
#define B1PIN 2 // P2.2
#define B2PIN 3 // P2.3
#define G1PIN 4 // P2.4
#define G2PIN 5 // P2.5

while(1)
       /* Output to matrix display */
        GPIO0 FIOPIN: OEPIN bit = 1 // Disable output
       /* Select row */
         GPIO1 FIOPIN: APIN bit = 1
         GPIO1 FIOPIN: BPIN bit = 1
         GPIO0 FIOPIN: CPIN bit = 1
       /* Output color */
                 for(i = 0; i < 32; i++){
                   if row<8 
                      GPIO2 FIOPIN: B1PIN bit = matrix[row][i]
                   else if(row>7)
                      GPIO2 FIOPIN: B2PIN bit = matrix[row][i]
                      GPIO0 FIOPIN: CLOCKPIN bit = 1
                      GPIO0 FIOPIN: CLOCKPIN bit = 1
         GPIO0 FIOPIN: CLOCKPIN bit = 1
         GPIO0 FIOPIN: LATCHPIN bit = 1
         GPIO0 FIOPIN: OEPIN bit = 1

Mp3 Player

Our focus in this project wasn't on the the Mp3 Player but rather on the whole system, a player with LED equalizer display. Therefore our player is rather simple, it consists of one task will read a song list from a text file then put song names into a vector. After that, it just reads the file in order then sends to the audio decoder to decode and output sound to a speaker and the equalizer analyzing circuit.

Pseudo code for Mp3_Player task: 

    open(songlist.txt) //read the songlist
    gets(line) //read line
    songnameVector.push_back(line) //push song names into vector
    while(open(songnameVector.front().c_str()) //open file from the SD card
        sendtoDecoder(buffer) //send data to the decoder
    songnameVector.rotateRight() //rotate the vector to get the next songname

Equalizer Circuit

The following is the code to start the equalizer and to collect the 7 spectrum values:

while(1) 

   {
       reset.setHigh();
       delay_us(1);
       reset.setLow();
       delay_us(75);
       for(int i=0;i<7;i++)
       {
           strobe.setLow();  //strobe is strobe
           delay_us(40);
           spectrum[i] = adc0_get_reading(3)/40.96; // Read the value of ADC-3
           strobe.setHigh();
           delay_us(40);
       }
    }


Implementation

Audio Decoder Driver

To set up the audio decoder, VS1053, these are the basic steps: 

   Do a hardware reset
   Set up the Mode Register //for normal operation use 0x0800
   Set up BASS/TREBLE Register //set to the value desired
   Set up the Clock Register //0x2000 for default clock 12 288 000 Hz
   Set up the AudioData Register //0xAC45 for sample rate of 44100 Hz
   Set up the Volume Register

To send a song to the audio decoder, VS1053, these are the basic steps: 

   Check DREQ signal //wait if it is 0 -- busy
   Send 32 bytes of data //as recommended by the manufacturer
   Read the AdditionalParameters Register //to see if any actions needed

Testing & Technical Challenges

Following is our encountered issues during our testing processes. These can be treated as an experience for future attempts at this kind of project.

Include sub-sections that list out a problem and solution, such as:

Issue #1: Programming LED matrix

Our original plan was to output graphic equalizer via a 16-by-32 LED matrix. However, the matrix's library was intended for Arduino, and we could not find a way to port the library to the LPC1758. In the end, we decided to output the graphic equalizer via five LED's on a breadboard, instead. We advise future aspiring engineers to research about available libraries or ask an expert before attempting to interface hardware with a microcontroller.

Issue #2: Additional PWM signal

Our design needed seven PWM signals in order to properly display each of the seven bands. The SJ-One board provides six PWM pins for use. We tried to configure a another pin, P0.20, as a PWM pin but were unsuccessful. We had a choice of using six or five PWM signals to display the equalizer. In the end, we decided to use five PWM signals for symmetry. For the LED display, The 160 Hz and 6250 Hz bands were not used.

Issue #3: GPIO pin defective issue

Our hardware design for the connection between the board and the VS1053 IC originally used pin 0.29 as the control signal for CS of the audio decoder. However, the original design didn't work. The issue was the GPIO pin 0.29 of the SJSU One board; it might be defective or require a pull up resistor. Everything worked just fine with pin 1.22 as the new CS pin. This issue took us some time to figure out since we were into Serial Clock Speed issue assumption. So for future reference, if you encounter this problem, when you cannot control CS signal the audio decoder at all, try to check the output level of all the GPIO pin first. It might save you some time.

Conclusion

An MP3 player is an embedded system because within a greater electrical system, the player has the express purpose of opening MP3 audio files and outputting the audio frequency via LED's, through a graphic equalizer circuit. The LPC1758 microcontroller uses SPI bus to communicate with the MicroSD card to read the audio file and VS1053 audio decoder, which then outputs to a seven-band graphic equalizer MSGEQ7 that splits the audio into several bands of varying frequencies, as well as to a speaker system. Rows of LED's display the filter levels of each band.

Programming the audio decoder involves resetting the hardware, then setting proper registers (mode, bass/treble, clock, etc.) for sound levels and data. Sending a song to the decoder sends the title and other relevant metadata to a vector.

Project Video

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Project Source Code

References

Acknowledgement

Acknowledgements to Sparkfun for providing components used, as well as lab instructor Preet Kang for his guidance in this project and throughout the semester. Special thanks to this group for a very detailed guidance to complete the mp3 player. They actually built a very convenient library used for simplifying the cstring operation. And we used it as is in our project for reading/storing file names.

References

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