Week 9 - Output Devices

17.11.2021 — weekly — 1 min read

This week I wanted to take a step forward towards displaying my PONG game on an LED matrix. To do so, I found at the lab an LED 32x32 RGB matrix. This looked like the perfect device to display my game:

The downside of finding random devices in the lab is that you never know where they come from or in what condition they are. I found online the datasheet which is far from being any detailed, so I had to spend some time thinking how to make the device work. I knew that it needs 5V power, DIN and GND. I tried to strip some bare wires and solder them directly on the matrix:

At the beginning I tried to power and ground it through my last week's breakout board but that showed no signal, so I connected the wires to an external 5V supply. I used the NeoPixel default example code to make sure my code is not the problem. Unfortunately, after many tries I had to figure out that either I am not connecting the device in a proper way or it is just defected. So I had to swap my output device with something I knew was working. I decided to program my PONG game on the OLED SSD 1306 display. I used Lingdong's awesome tutorial to bootstrap my display (code is attached below).

Now I coded a simply ball movement:

1// ball config
2int ball_x0;
3int ball_y0;
4int ball_dx = 1;
5int ball_dy = 1;
6int ball_x;
7int ball_y;
8int ball_speed = 50;

1// draw ball
2ball_x = ball_x0 + ball_dx;
3ball_y = ball_y0 + ball_dy;
4OLEDpixel(ball_x, ball_y);
5OLEDunpixel(ball_x0, ball_y0);
6
7// ball boundaries
8if (ball_y >= 63) {
9  ball_dy = -1;
10}
11if (ball_y <= 1) {
12  ball_dy = 1;
13}
14if (ball_x >= 127) {
15  ball_dx = -1;
16}
17if (ball_x <= 2) {
18  ball_dx = 1;
19}
20
21// update ball iteration
22ball_x0 = ball_x;
23ball_y0 = ball_y;
24
25// display
26OLEDflush();
27delay(ball_speed);

For some reason, the display flickered at the bottom part. At the beginning I though it has something to do with the way I convert integers to pixel locations on the OLED buffer. After debugging for a while I could not find any code mistakes so I assumed that my display was defected. I tried another OLED display with the same code:

And I was right! I used the rest of my time to program the players controllers and movement. In the future, those should be controlled via the distance ToF sensor I experimented with last week.

1// players config
2#define CONTROLLER_W 4
3int winner = 0;
4int p_y0 = 32;
5int p1_y= p_y0;
6int p2_y= p_y0;
7int d_p1 = 1;
8int d_p2 = -1;

1void drawPlayerController(int player_loc, bool isPlayerOne) {
2  int x_offset = 2;
3  if (!isPlayerOne) {
4    x_offset += 125;
5  }
6
7  for (int j = 0; j < 64; ++j) {
8    OLEDunpixel(x_offset, j);
9  }
10  
11  for (int i = 0; i < (2 * CONTROLLER_W + 1); ++i) {
12    int loc = player_loc - CONTROLLER_W + i;
13    OLEDpixel(x_offset, loc);
14  }
15  
16}

Week 9 - Output Devices

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