F20: Hungry Snake

Abstract

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Objectives & Introduction

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Team Members & Responsibilities

• Yang Chen
  • Game Development, Code Repo Management
• Yanshen Luo
  • Hardware Development
• David Tang
  • Game Development
• Nuoya Xie
  • Hardware Development - LED Matrix, Controller, and PCB Design

Schedule

TEAM SCHEDULE
Week#	Date	Task	Status
1	10/10/20	Place an order for LED matrix Initial delegation of tasks for different parts of the project Set up splitwise for splitting expenses	Complete Complete Complete
2	10/17/20	Determine initial project content and scope Determine game stages Set up project Git repository	Complete Complete Complete
3	10/24/20	Determine project software architecture Come up with a more detailed spec of the game Plan out how to distribute tasks for software game components Specify smaller code modules needed and start programming	Complete Complete Complete Complete
4	10/31/20	Start developing prototype of game logic for various games screens Start creating LED matrix driver Start creating controller driver	Complete Complete Complete
5	11/7/20	Display letters in LED matrix Detect joystick and button state from controller Develop prototype for snake movement logic and border detection/collision	Complete Complete Complete
6	11/14/20	Start design of interfacing board between LPC and other components of the system Testing LED matrix and controller driver Ability to print game state on console for debugging purposes Initialize game state with multiple sprites Determine feasibility of MP3 decoding as game feature Start game enclosure design	Complete Complete Complete Complete In progress In progress
7	11/21/20	Finish interface board design Start developing prototype for displaying a score board logic Testing of LED matrix and controller drivers complete Initial combination of software and hardware implementation Finish game enclosure	Complete Complete Complete
8	11/28/20	Refine and add more features to the game specs Complete playable MVP Fine tune the game logic and playability
9	12/5/20	Testing all components (software, hardware) working as expected Game enclosure created and game enclosed
10	12/12/20	Testing all components working together as expected Finalize Wiki report
11	12/16/20	Demo Day

Parts List & Cost

Top Level
PART NAME	PART MODEL & SOURCE	QUANTITY	COST PER UNIT (USD)
64x64 RGB LED Matrix*	Adafruit	1	$54.95
5V 5A PSU	Amazon	1	$14.99
SJ2 Board	-	2	FREE (each team member has his/her own)
10 pin IDC flat Ribbon Cable	Amazon	1 roll	$7.99
2x5 FC-10P 2.54mm Dual Rows IDC Sockets Female Connector	Amazon	2	$0.46

Interface Board
Item #	PART NAME	PART SOURCE	QUANTITY	COST PER UNIT (USD)
1	2 x 20 (40 Pin) Extra Tall Female 0.1 Inch Pitch Stacking Header	Amazon	1	$1.375
2	2X5 10Pins 2.54mm Pitch Straight Pin Connector IDC Header	Amazon	1	$0.24
3	2X8 16Pins 2.54mm Pitch Straight Pin Connector IDC Header	Amazon	1	$0.28
4	TB006-508-02BE Screw Terminal Block	DIGIKEY	1	$0.77
5	RSTA 3.15 AMMO Fuse	DIGIKEY	1	$0.28
6	TB005-762-02BE Screw Terminal Block	DIGIKEY	1	$0.85
7	2.1mm Barrel Jack Female	DIGIKEY	1	$0.71
8	2.1mm Barrel Jack Female (Breadboard Compatible)	Provided by Yanshen Luo	1	Free
9	3mm LED	Provided by Nuoya Xie	1	Free
10	680Ω resistor	Provided by Nuoya Xie	1	Free

Controller Board
Item #	PART NAME	PART SOURCE	QUANTITY	COST PER UNIT (USD)
1	Analog 2-axis Thumb Joystick w/ select button	AMAZON	1	$1.6
2	12x12x7.3 mm Tactile Push Button	AMAZON	2	$0.64
3	2X5 10Pins 2.54mm Pitch Straight Pin Connector IDC Header	Amazon	1	$0.24
4	LSM303 Triple-Axis Accelerometer	DIGIKEY	1	$14.95
5	standoff with accompany screw and nut	Provided by Nuoya Xie	2	Free
6	2.5mm Female Headers (1x8)	Provided by Yanshen Luo	1	Free
7	3mm LED	Provided by Nuoya Xie	1	Free
8	330Ω resistor	Provided by Nuoya Xie	1	Free

Design & Implementation

The design section can go over your hardware and software design. Organize this section using sub-sections that go over your design and implementation.

Interface Board Design

Interface Board Finished Product

The purpose of the interface board is to provide stable, permanent connection to the SJ2 board. It includes connections to all the components that are necessary for the game to run. Below are the components of the interface board:

1. 2x20 0.1" pin header to connect to the SJ2 board
   
2. 3.15A fuse to prevent high current passing through the components, in case of an electrical short
   
3. IDC 2x8 shroud connector to the LED matrix signal pins
   
4. Screw terminals for power to the LED matrix(5V), as well as 5V inlet power from power supply
   
5. Optional 2.1mm DC barrel jack for 5V inlet power. Either this jack or the screw terminal can be used to feed power into the interface board
   
6. LED with a current-limiting resistor, indicting when power is provided to the board
   

In order to save manufacturing costs, the interface board is designed so the footprint of the board is as small as possible. The board is a standard two-layer board with silkscreen on both sides. We went with JLC (https://jlcpcb.com/) to manufacture our board.

Interface Board Schematic

Interface Board PCB Layout

Interface Board PCB

Controller Board Design

Controller Board Finished Product

The purpose of the controller board is to obtain user feedback to the game. Similar to a real controller, the controller board contains one joystick that can detect five different directions (up, down, left, right, and center). This is used to control movement of the snake in game. Two buttons, confirm(green) and cancel(red) are included on the board so they can be used to select options on the opening screen. An accelerometer, LSM303, is attached to the controller board through female headers for the ease of removal, in the event which the accelerometer needs to be replaced. The controller board also contains an LED to indicate that the board has been supplied of power. The communication between the controller board and the interface board is through and IDC 10-pin header and ribbon cable. The reason why flat ribbon cable is selected is because the crimper, header, and wire for such cable is cheap and readily available.

Controller Board Schematic

Controller Board PCB Layout

Controller Board PCB

The controller board is designed to be a narrow rectangular so the footprint of the board is as small as possible, yet give enough space for hands to grab confortably. The board is a standard two-layer board with silkscreen on both sides. Similar to the interface board, we went with JLC (https://jlcpcb.com/) to manufacture our board.

Hardware Interface

LED Matrix Display

64 X 64 LED Matrix

LED Matrix Pinout

We chose an 64 x 64 LED Matrix from Adafruit, because we wanted the number of pixels to be as many as possible. The display is controlled by an 2x8 IDC header, which has the following pins:

• R1, G1, B1 - Pins controlling Red, Green, and Blue colors for the upper half of the matrix (32 x 64 LEDs)
• R2, G2, B2 - Pins controlling Red, Green, and Blue colors for the lower half of the matrix (32 x 64 LEDs)
• A, B, C, D, E - Multiplexer pins selecting a single row of the matrix (2 ^ 5 = 32 rows)
• CLK - Clock signal that indicating each shift into the shift register of the LED matrix
• LAT - Once data is shifted into the shift register of the LED matrix, this pin latches the data so they won't be altered
• OE - Output Enable. Used to on the selected row's LEDs on or off

Because we are using 1 bit for each color, a total of 2^3 = 8 colors are available for us to pick from. This also means that all of the pins listed above are simply GPIO pins to control the LED matrix.

At any one point in time, 2 rows (1 on the upper half of the matrix and 1 on the bottom) are selected. These two rows are always off by 32. For example, if row 0 on the top half is selected, then row 0 on the bottom half, which is row 32, is also selected. This means at any one time, two rows are lighted up. However, because of the persistence of vision, human eye can only perceive image at and below 60Hz. This mean if we shift the bits fast enough, we are able to light up "all" of the LEDs on the matrix display.

Controller

Controller consists of:

• One joystick, capable of detecting 5 directions - up, down, left, right, and none (when the controller is not moved)
• Two buttons, one for confirming and one for cancelling of selected options on the start screen
• An accelerometer, LSM303, for detecting movement, such as the shaking of controller by user

Joystick consists of two potentiometers, one for horizontal and one for vertical. When user pushes the stick to a certain direction, both potentiometer contacts are swept across two contacts, creating two voltage dividers. Thus, but reading this voltage using two ADCs, the direction of horizontal and vertical movement can be calculated.

Buttons are connected to GPIO pins that are input direction with a pull-up resistor. When the button is pressed, the input line is connected to ground. Thus, by reading the input pins, if the pin is low, the button is pressed, and vice versa.

Accelerometer

LSM303 triple-axis accelerometer from Adafruit

Accelerometer (LSM303) is used in this game to detect controller motion. The sensor can detect acceleration in the x, y, and z coordinate. In our application, we used the z coordinate acceleration to calculate if the controller is been moved up and down. The sensor communicates to the JS2 board using I2C protocol, which means an SDA and SCL lines, on top of GND, are connected to the I2C2 peripheral of the microcontroller board.

Software Design

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LED Matrix Display

In order to control the LED matrix and give each pixel its color, the user has to:

1. Select which row (on both top and bottom half of the matrix) using pins A ~ E
2. Disable output on this row of LEDs by setting OE pin
3. Unlatch data by setting the LAT pin
4. For each pixel on the row, clear first, then shift the desired bits into R1, G1, B1, R2, G2, and B2 pins. Set and Reset the CLK pin for each LED.
5. Enable output by resetting the OE pin
6. Have some delay. The longer the delay, the brighter the pixel will be
7. Lastly, disable output by setting the OE pin

All of this code is encapsulated into a function, which is called by a FreeRTOS display task that has highest priority and runs every 10ms. The flow diagram of the display tasks is shown below.

File:Fall2020 group6 display task.JPG Display Task

Below is the code describing the steps above.

void led_matrix__refreshDisplay(void) {
  for (uint8_t row = 0; row < LED_MATRIX_HALF_LENGTH; row++) {

    led_matrix__select_row(row);
    led_matrix__disable_output();
    led_matrix__unlatch_data();
    led_matrix__clock_in_data(row);
    led_matrix__latch_data();
    led_matrix__enable_output();
    delay__us(100);
    led_matrix__disable_output();
  }
}

Select Row function:

void led_matrix__select_row(uint8_t row) {
  // set all rows to low first
  LPC_GPIO1->PIN &= ~(1 << D.pin | 1 << E.pin);
  LPC_GPIO2->PIN &= ~(1 << A.pin | 1 << B.pin | 1 << C.pin);

  // row number selected using A to E (5 bits)
  LPC_GPIO2->PIN |= (((row >> 0) & 0x1) << A.pin | ((row >> 1) & 0x1) << B.pin | ((row >> 2) & 0x1) << C.pin);
  LPC_GPIO1->PIN |= (((row >> 3) & 0x1) << D.pin | ((row >> 4) & 0x1) << E.pin);
}

Below is the clock in data function:

void led_matrix__clock_in_data(uint8_t row) {
    for (uint8_t col = 0; col < LED_MATRIX_FULL_LENGTH; col++) {
        LPC_GPIO2->PIN &= ~((1 << R1.pin) | (1 << R2.pin) | (1 << G1.pin) | (1 << G2.pin) | (1 << B1.pin) | (1 << B2.pin));

        LPC_GPIO2->PIN |= (display_matrix_top[row][col].R << R1.pin) | (display_matrix_bottom[row][col].R << R2.pin) |
                      (display_matrix_top[row][col].G << G1.pin) | (display_matrix_bottom[row][col].G << G2.pin) |
                      (display_matrix_top[row][col].B << B1.pin) | (display_matrix_bottom[row][col].B << B2.pin);

        lab_gpio__set(CLK.port, CLK.pin, true);
        lab_gpio__set(CLK.port, CLK.pin, false);
  }
}

Controller

All of the controller-related actions are encapsulated in two FreeRTOS tasks. One is a controller setter task that obtains values from controller joystick and buttons. Another is a getter task that gets the current controller-related values from the stored values obtained in the setter task. Both of these tasks are run at 100ms and are low priority. A mutex is used between the tasks to prevent simultaneous access to the resource, in this case a structure that stores the current controller values.

File:Fall2020 group6 controller tasks.JPG Controller Getter and Setter Tasks

Implementation

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Testing & Technical Challenges

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

<Bug/issue name>

Discuss the issue and resolution.

Conclusion

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Project Video

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Project Source Code

• Sourceforge Source Code Link

References

Acknowledgement

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References Used

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Appendix

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