Difference between revisions of "F20: Space Invaders"

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[[File:Schematic_244_spaceinvaders.png|890x890px|thumb|center|PCB Schematic]]

Revision as of 00:46, 18 December 2020

Space s20cover.png
Final Result


  • Final Result
  • Win Gameplay
  • Lost Gameplay


Space Invaders is a fixed one person shooter style video game. The player controls a laser cannon by moving it horizontally across the bottom of the screen and firing at the aliens descending toward the cannon from the top of the screen. There are aliens descending towards the cannon and the player's main goal is to defeat an alien and earn points by shooting it with the laser cannon and destroying it. As more aliens are defeated, the aliens' movement speeds up. The alien invasion is declared successful and the game ends when the aliens have successfully reached the bottom. The final score of total kills is projected after the game ends. The mp3 decoder connected to the speaker will play the sound effects required.

Space Invaders High Level Architecture


About the Game

The object of the game is, basically, to shoot the invaders with your laser cannon while avoiding their shots and preventing an invasion. Amassing a high score is a further objective and one that must be prioritized against your continued survival. Each game screen starts with 3 rows of 4 invaders. The enemies will be shooting at the laser cannon seeking to destroy it in order to invade the earth. The person controlling the laser cannon must avoid getting blown out by the enemies. As more enemies are destroyed the difficulty increases with the speed of the enemies increasing towards the earth. The laser cannon can survive 5 enemy bullets.


  • Interface the 64x64 RGB LED Matrix with SJ-Two Microcontroller.
  • Interface the VS1053 MP3 Decoder with another SJ-Two Microcontroller.
  • Interface MAX98357A Mono Amplifier via I2S.
  • Establish UART communications between the two SJ-Two Microcontrollers.
  • Create simple coding logic for displaying required characters and game objects.
  • Have required sound effects at different functions of the game.
  • Have multiple display screens at different stages of the game.

Team Members

Technical Responsibilities

Administrative Roles
  • Game Logic Development
Salvatore Nicosia & Akash Vachhani
  • PCB Design
Akhil Cherukuri
  • LED Display Driver
Salvatore Nicosia
  • Graphics Driver
Salvatore Nicosia & Akhil Cherukuri
  • Splash Screen Graphics Driver
Akhil Cherukuri
  • Mp3 Decoder
Akash Vachhani
  • Enclosure
Salvatore Nicosia
  • Hardware Integration
Salvatore Nicosia & Akhil Cherukuri

Administrative Responsibilities

Administrative Roles
  • Team Leader
Salvatore Nicosia
  • Git Repository Managers
Salvatore Nicosia & Akash Vachhani
  • Code Reviewers
Salvatore Nicosia & Akash Vachhani
  • Wiki Report Manager
Akhil Cherukuri
  • Bill of Materials Manager
Akhil Cherukuri


Week# Start Date End Date Task Status
  • 10/12/2020
  • 10/18/2020
  • Read previous projects, gather information, and discuss among the group members.
  • Create a GitLab repository for the project [10/13/2020]
  • Completed
  • Completed
  • 10/19/2020
  • 10/20/2020
  • Acquire parts: LED Matrix, VS1053 Mp3 decoder breakout board by Adafruit
, 2X Analog 2-axis thumb joystick with select button + breakout board

  • Completed
  • 10/26/2020
  • 11/01/2020
  • Read and familiarize with LED Matrix Datasheet
  • Read and familiarize with MP3 Decoder VS-1053 datasheet.
  • Completed
  • Completed
  • 11/02/2020
  • 11/08/2020
  • Develop graphics driver for LED matrix and implement initial game objects
  • Develop driver for MP3 decoder
  • Read MP3 data from Micro SD Card
  • Completed
  • Completed
  • Completed
  • 11/09/2020
  • 11/15/2020
  • Finalize wiki schedule [11/10/2020]
  • Circuit Simulation in EasyEDA/Eagle Tool.
  • PCB Layout Design in EasyEDA/Eagle Tool.
  • Finalize component placement on PCB.
  • Order PCB from JLCPCB.
  • Create 3D printed enclosure and extra accessories
  • Completed
  • Completed
  • Completed
  • Completed
  • Completed
  • Completed
  • 11/16/2020
  • 11/22/2020
  • Assemble components to circuit boards
  • Extensively test circuit boards in two rounds
  • Develop game logic for space ship movement and monsters respawn
  • Develop splash screen and menu selection
  • Finalize selection of MP3 tracks for in-game sounds
  • Completed
  • Completed
  • Completed
  • Completed
  • Completed
  • 11/23/2020
  • 11/29/2020
  • Implement game difficulty logic as enemies count decreases
  • Integrate circuit boards and check proper connections to the components and the microcontrollers
  • Integrate game logic code with LED matrix
  • Integrate game sounds with game logic
  • Completed
  • Completed
  • Completed
  • Completed
  • 11/30/2020
  • 12/06/2020
  • Additional Features: Lives, Health Level Bars
  • Integrate subsystem and ensure proper connection and communication between peripherals
  • Integrate all components and finalize 3D printed enclosure
  • Update the wiki page.
  • Completed
  • Completed
  • Completed
  • Completed
  • 12/07/2020
  • 12/13/2020
  • Address bugs during testing of the integrated system
  • Test play/restart functionality
  • Test music and effects are synchronized with the game
  • Completed
  • Completed
  • Completed
  • 12/14/2020
  • 12/16/2020
  • Update Gitlab repo with complete and working code.
  • Create Project Demo video and upload it to YouTube.
  • Update the wiki page to the final version.
  • Final Demo [12/16/2020]
  • Completed
  • Completed
  • In Progress
  • Completed


Item# Part Description Part Model & Vendor Quantity Cost
1 Microcontroller Boards SJ2 Boards (Purchased from Preet Kang) 2 $100.00
2 LED Matrix Display Sparkfun RGB LED Matrix Panel - 64x64 1 $80.00
3 Arcade Buttons and Joystick Kit Arcade Buttons and Joystick Kit EG STARTS 1 $25.94
4 Capacitive Touch Switch Button Self-Lock Module DAOKI TTP223 Capacitive Touch Switch Button Self-Lock Module 2 $7.56
5 MP3 Decoder Adafruit VS1053 Mp3 Decoder Breakout Board 2 $24.95
6 Black PLA 3D Printer Filament HATCHBOX PLA 3D Printer Filament 1.75mm 1 $25.12
7 White PLA 3D Printer Filament HATCHBOX PLA 3D Printer Filament 1.75mm 1 $25.12
8 Power Supply 5V 18A MEAN WELL LRS-100-5 AC/DC Switching Power Supply 90W 5V 18A Single Output 1 $21.30
9 Rocker Switch Power Socket Inlet Module Plug 3Dman 15A 250V Rocker Switch Power Socket Inlet Module Plug 5A Fuse Switch with 18 AWG Wiring 3 Pin IEC320 C14 1 $8.73
10 Speaker 3" Adafruit Accessories Speaker 3" (1 piece) 1 $6.58
11 Mono Amplifier Adafruit I2S 3W Class D Amplifier Breakout - MAX98357A 2 $5.95
12 USB DC Buck Step Down Module HiLetgo 5pcs DC-DC Buck Step Down 6-24V to 5V 3A USB Module 1 $7.59
13 Prototype PCB LampVPath (Pack of 2) PCB Prototype Board 1 $6.99
14 Ribbon Cables 40pin Antrader 30CM 40-Pin IDC Connector Flat Ribbon Cable 1 $9.99
15 Ribbon Cables 16pin Antrader 30CM 16-Pin IDC Connector Flat Ribbon Cable 1 $8.99
16 Header Pins 2 x 8 pin Antrader 30PCS 16 Pin 2 x 8 Male Box Header 1 25.60
17 Header Pins 2 x 20 pin Antrader 24Pcs 2 x 20 Pin 40 Male Box Header 1 9.99
18 PCB JLCPCB Set of 5 1 25.60


Design And Architecture

The complete printed circuit board was designed using EasyEDA online software. Implemented both SJ-Two board connectors along with required connections to buttons, led matrix, touch sensors, joystick, VS1053 MP3 Decoder, and MAX98357A I2S Amplifier.

PIN Configuration

  • PIN# SJ-2 Main Board Pin Description uC PIN
    64x64 LED MATRIX
    R1 PIN for Red terminal of RGB LED for the upper half of LED Matrix P2_0
    G1 PIN for Green terminal of RGB LED for the upper half of LED Matrix P2_1
    B1 PIN for Blue terminal of RGB LED for the upper half of LED Matrix P2_2
    R2 PIN for Red terminal of RGB LED for the lower half of LED Matrix P2_4
    G2 PIN for Green terminal of RGB LED for the lower half of LED Matrix P2_5
    B2 PIN for Blue terminal of RGB LED for the lower half of LED Matrix P2_6
    A Mux pin for row selection P2_7
    B Mux pin for row selection P2_8
    C Mux pin for row selection P2_9
    D Mux pin for row selection P0_16
    E Mux pin for row selection P0_15
    OE Output Enable P1_28
    LATCH Data Latch P1_29
    CLK Clock Signal P0_17
    VCC VCC Supply VCC
    GND Ground GND
    TX UART Transmit P4_28
    RX UART Receive P4_29
    Pin 2 Right Movement P1_31
    Pin 3 Left Movement P1_30
    I/0 Pin Shoot P0_25
    I/0 Pin Start P0_26
  • PIN# SJ-2 Music Board Pin Description uC PIN
    VCC VCC Supply VCC
    GND Ground GND
    TX UART Transmit P4_28
    RX UART Receive P4_29
    VS1053 MP3 DECODER
    SCK_2 CLOCK for SPI Bus P0_7
    MOSI_2 MISO for SPI Bus P0_8
    MISO_2 MOSI for SPI Bus P0_9
    DREQ Data Request P2_0
    SDCS Transfer SCI commands P2_2
    XDCS Transfer the Audio Data P2_5
    RESET Reset for Decoder P2_7
    GPIO 4 (I2S_LROUT) I2S Audio Out LRC
    GPIO 6 (I2S_SCLK) I2S Salve Clock BCLK
    GPIO 7 (I2S_SDATA) I2S Slave Data In DIN
    LRC I2S Audio Out GPIO 4
    BCLK I2S Salve Clock GPIO 6
    DIN I2S Slave Data In GPIO 7
    I/0 Pin Volume Up P0_26
    I/0 Pin Volume Down P0_25


  • PCB was sent to fabrication to JLCPCB China which provided PCB with an order of 5 and 2 layers of PCB and common grounded the rest of the copper area.

DRC elements (in mm)

  • Track Width = 0.254
  • Clearance = 0.152
  • Via Diameter = 0.61
  • Via Drill Diameter = 0.305

  • PCB Top Layer
  • PCB Bottom Layer

  • PCB Schematic


Hardware Interface

This project utilizes as a display a 64x64 RGB LED Matrix Panel with a scan rate of 1:32. The LED matrix panel has 4096 RGB LEDs which can be controlled and addressed individually. Because 4069 LEDs would be impossible to connect to the sjtwo board since it does not have sufficient GPIOs, this LED Matrix utilizes only 13 digital GPIOs to provide full control of each individual LED. To achieve this, the LED matrix uses a decoder to select the rows and a 64-bit shift register which enables the desired color on the selected column. When the row selection is low the columns are selected by clocking in data into the shift register. This 64x64 LED matrix has 6 64-bit shift registers for R1, G1, B1 R2, G2, B2 where each color of the LED is controlled by one bit of the shift register. Since this display uses shift registers which are daisy chained, there is no capability to control each LED using PWM and therefore the display only supports 8 colors. Shown below is a diagram of the LED matrix showing the top half (Rows 0-31) and bottom half (Rows 32-63) which are controlled by 5:32 decoders. These decoders have a 5-bit input for each line A, B, C, D, E and are used for row selection. The diagram also shows six shift registers R1,G1,B1 for the top half, and R2, G2, B2 and for bottom half which are used for column selection and selecting the appropriate LED color. The data is clocked into these shift registers which hold all 64 bits for every single row. The LAT (Latch) signal is used to latch the data after each color has been clocked into the shift registers so that it can reach the output driver when set to high. The latch is then closed so that the next row of data can be clocked in. The OE (Output Enable) signal is used to enable the output when this pin is low so that the LEDs are turned on showing the data previous latched. Before switching rows the OE signal is then pulled high so that no LEDs are on during this transition.

LED Matrix

The LED matrix was interfaced with the SJTwo board using 13 GPIO pins connected to data in connector as shown in the diagram below. The LED matrix is powered by an external 5V 18amp power supply which is used for the overall system in addition to the LED matrix. The GPIO pins were chosen in such a way that they are close to each other for simplicity and wire organization.

Below are the technical specifications of the Sparkfun RGB LED Matrix Panel 64x64:

Spec Value
Pitch 3mm
Resolution 64 x 64 = 4096 dots
Panel dimensions 192 x 192mm
Working voltage/current rating 5v / 60A (max)
Scan Rate 1 / 16
Port Type HUB75-A
Weight 0.3 kg

LED Matrix Schematic

LED Matrix Driver

The LED matrix driver was designed based on the basic mechanism described below:

For each row of leds we repeat these steps:

  1. Set the latch and output enable pins to low to clock in the next row of data and enabling the output so that the leds are turned on
  2. For each column, clock in the data for the current row one bit at a time into the shift registers (R1, G1, B1, R2, G2, B2)
  3. Set the latch and output enable pins high to allow the row of data to reach the output driver while disabling the output so that no LEDs are on while switching rows
  4. Select the row by driving the appropriate row select lines (A,B,C,D,E)

Below is a snippet of code showing how the LED matrix displays the pixels based on the mechanism described before.

void led_matrix__display_pixels(void) {
  for (uint8_t row = 0; row < 32; row++) {
    for (uint8_t column = 0; column < 64; column++) {
      (matrix_buffer[row][column] & 0x1) ? gpio__set(B1) : gpio__reset(B1);
      (matrix_buffer[row][column] & 0x2) ? gpio__set(G1) : gpio__reset(G1);
      (matrix_buffer[row][column] & 0x4) ? gpio__set(R1) : gpio__reset(R1);
      (matrix_buffer[row][column] & 0x8) ? gpio__set(B2) : gpio__reset(B2);
      (matrix_buffer[row][column] & 0x10) ? gpio__set(G2) : gpio__reset(G2);
      (matrix_buffer[row][column] & 0x20) ? gpio__set(R2) : gpio__reset(R2);


The LED matrix driver was written for a 64x64 display but can be easily re-adapted for other display sizes. This driver was kept as simple as possible and includes the following APIs which are available to the programmer to fully control each individual pixel. Only 8 colors are available in this driver since the LED matrix uses shift registers.

void led_matrix__clear_display(void);
void led_matrix__set_pixel(uint8_t row, uint8_t column, led_color_e color);
void led_matrix__clear_pixel(uint8_t row, uint8_t column);

The data is stored into a 32x64 buffer and in order to correctly display the colors the top and bottom half of the display use the following mask values:

static uint8_t bottom_half_of_display_mask = 0x07;
static uint8_t upper_half_of_display_mask = 0x38;

Software Design

A high priority task is used to consistently refresh the LED matrix display which simply calls the led_matrix__display_pixels() API. All the game graphics and basic graphics such as numbers and letters were implemented in separate modules to keep the code base portable. The splash screen and game over screen were implemented using lookup tables and both are controlled by two separate tasks which check the status of the game and display the right screen accordingly. The victory screen was implemented by using the same graphics components used in the game logic and it also controlled by a task which checks for winning status of the game. In the images below are shown all the graphics components of the game as wells as all the different screens based on the status of the game. The graphics components of the game include, the explosion, laser cannon, enemies (octopus, crab, and squid), ufo, laser cannon bullet, enemies bullet, as well as the score board and lives. These graphics were designed by using the set_pixel() API of the LED matrix driver and it allows the user to pass in just the column position, row position, and color to display the object in the desired space of the display.

  • Splash Screen
  • Game Play Screen
  • Victory Screen
  • Game Over Screen


Hardware Interface

In this section, you can describe how your hardware communicates, such as which BUSes used. You can discuss your driver implementation here, such that the Software Design section is isolated to talk about high level workings rather than inner working of your project.

<Discuss here about MP3 decoder hardware>

MP3 board schematic

MP3 Decoder Driver

<Discuss here about MP3 player driver>

Software Design

Show your software design. For example, if you are designing an MP3 Player, show the tasks that you are using, and what they are doing at a high level. Do not show the details of the code. For example, do not show exact code, but you may show psuedocode and fragments of code. Keep in mind that you are showing DESIGN of your software, not the inner workings of it.



Arcade Buttons

Touch Sensors



The game logic uses an object oriented approach in which all the enemies, laser cannon, and bullets are created as objects. This design choice was done to simplify the game logic and to easily identify the object's column position, row position, moving direction, width, height, entity, subtype, color, validity, and points worth. The game consists of only 6 type of objects and are the following:

  • CRAB

Project Structure

│   ├───led_matrix
│   └───mp3_decoder
│   ├───game_graphics
│   ├───game_logic
│   ├───gpio_isr
│   └───led_matrix_basic_graphics


Space Invaders UART Connection

Game tasks

The game consists of the following tasks:

  • Refresh Display_task
  • LED Decorative Sign task
  • Display Scoreboard task
  • Start Screen task
  • Victory Screen task
  • Game Over Screen task
  • Move Laser Cannon task
  • Move Enemies task
  • Laser Cannon Shooting task
  • Enemy Shooting task
  • Kill Animation task

Refresh Display Task

This task is responsible for calling the led matrix driver function to display the pixels. The priority of this task is set to High.

LED Decorative Sign Task

This task is just an added feature that has the job to always keep the first 3 rows of the LED Matrix on to light up the arcade machine marquee.

Display Scoreboard Task

This task displays the score board and lives only when the game is started.

Start Screen Task

This task continuously displays the splash screen if the game is not started. It also uses a binary semaphore to receive the interrupt when the start button is pressed. When the start button is pressed the game is reset, the display is cleared to move to the next screen and the task is suspended.

Victory Screen Task

This task checks the winning status of the game. If the game is won it clears the display, displays the victory screen, and sets back a boolean variable called is_game_started back to false. It also uses a binary semaphore to receive the interrupt when the start button is pressed. When the start button is pressed the game won status is set back to false and the start screen task is resumed.

Game Over Screen Task

This task checks the game over status of the game. If the game is over it clears the display, displays the game over screen, and sets back is_game_started back to false. It also uses a binary semaphore to receive the interrupt when the start button is pressed. When the start button is pressed the game over status is set back to false and the start screen task is resumed.

Move Laser Cannon Task

This task calls the move laser cannon function only when the game is started. Its only job is to enable the control of the laser cannon through the joystick.

Move Enemies Task

This task calls the move enemies function only when the game is started. Its only job is to move the enemies left to right and down. The logic behind this function involves checking how many enemies are left to determine the correct movement and increase the enemies movement speed.

Laser Cannon Shooting Task

This task updates the bullet location and uses a binary semaphore to receive the interrupt when the shooting button is pressed and call the shoot bullet function. These functions are called only when the game is started.

Enemy Shooting Task

This task calls check valid enemy to shoot bullet function only when the game is started. The logic behind this function involves choosing an enemy that is still alive and it is valid to shoot a bullet to the laser cannon.

Kill Animation Task

This task checks for the status when an enemy has been killed and it needs to show the killing animation. The job of this task is to simply suspend the move enemies task when an enemy has been killed so that for a brief instant all of the enemies are stopped while the killing animation is display and then is resumed again.



The 3D model design of the arcade cabinet was modified according to our needs to fit the LED matrix display. Credit goes to the designer of the model which can be found on thingiverse at this link. The model took a little over a week to be printed using a 0.2 resolution with 20% infill. The buttons for the volume were custom made with a thickness of 2mm so that touch sensors would detect the input from the user. Show below are pictures of the 3D model as well as the printed result.

  • 3D Print Model (Front)
  • 3D Print Model (Back)
  • 3D Print Model
  • 3D Print Model (Top)
  • 3D Print Model (Bottom)
  • 3D Print Model (Volume Buttons)

3D printed result

  • 3D Print Model (Front)
  • 3D Print Model (Back)
  • 3D Print Model (Left)
  • 3D Print Model (Right)
  • 3D Print Model (Side)
  • 3D Print Model (Inside)


LED Matrix Displaying Incorrect Colors

While testing the driver it was identified an issue with the LED matrix not displaying the correct colors or at times not displaying them at all in certain parts of the display. To analyze this problem different objects were drawn in different sections of the display to understand the cause of this behavior. While testing it was noticed that the LED matrix would display the correct color only when both the top 32 rows and bottom 32 rows were active or when at least one row was active in both sections. After debugging the code and ensuring that the logic to display the pixels was correct the problem turned to be that the cable that connects to HB75E connector of the LED matrix had a few defective pins which were causing issues on some of the registers that control the RGB colors. After extensively testing by drawing more objects it was deduced that the root cause of this issue was a bad cable.

PCB Design

While testing the ribbon cables, we have identified out that the purchased double row ribbon did not invert pin rows as a normal ribbon cable does.


Conclude your project here. You can recap your testing and problems. You should address the "so what" part here to indicate what you ultimately learned from this project. How has this project increased your knowledge?


We would like to express our gratitude to Professor Preetpal Kang for providing valuable insight and knowledge with us and for guiding us through the completion of this project. We would also like to thank Vidhusi Jain(ISA) for her valuable advice code reviews, and constructive feedback. Also a big shout-out to all of our classmates, for the great Slack discussions which provided solutions and necessary feedback.


Project Source Code

Project Video