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LED Matrix (Shifting Hollow Rectangle) Solution
LED matrixes are fun and compact components that allow a designer to display various shapes and colors.
How it works?
The LTP-2158AHR is a 5x8 LED matrix. The orientation of the LED matrix in the following diagrams and exercises has been chosen for simplicity
Two sets of pins, represented by RED and BLACK in the above diagram, are used to determine which LEDs are illuminated. You can determine the LED matrix orientation by finding the '1' on the back of the matrix next to pin 1.
The first set of pins (RED) control what pattern is displayed on a row of the LED matrix. The other set of pins (BLACK) control which row(s) display the pattern.
If a BLACK pin is grounded, then the pattern present on the RED pins will be displayed on the column associated with the grounded BLACK pin.
Below are some examples of the behavior of the LED matrix.
Prelab:
NOTE: The final challenge of this lab is to connect your LED Matrix using a shift register. If you feel confident you may complete all the parts using the shift register and get credit for the final challenge to reduce the amount of board rewiring.
1) Make the following connections from the microcontroller to the LED matrix:
IMPORTANT: Connect resistors between PD[4:0] and the LED matrix pins. Without the resistors in place, there is a risk of burning out the LEDs in the LED matrix.
Note: You may want to flip the orientation of your microcontroller 180 degrees. In the next lab we will be combining the LED matrix with a joystick. It is easier if the matrix is at the top of the breadboard and the joystick is at the bottom. Thus you would want
PORTC and PORTD oriented towards the top of your board near the LED matrix and
PORTA (required for analog control) oriented towards the bottom of the breadboard near the joystick.
PC7: pin 9 COL1
PC6: pin 14 COL2
PC5: pin 8 COL3
PC4: pin 12 COL4
PC3: pin 5 COL5
PC2: pin 1 COL6
PC1: pin 7 COL7
PC0: pin 2 COL8
PD4: pin 13 ROW5
PD3: pin 3 ROW4
PD2: pin 4 ROW3
PD1: pin 10 ROW2
PD0: pin 6 ROW1
No connection: pin 11
After making the above connections between the microcontroller and LED matrix, the diagram below shows how the pins of the microcontroller are mapped to the LEDs of the LED matrix.
2) Write a program to run a single synchSM. Copy and paste the code below into the program. This code will act as the synchSM. Set DDRC and DDRD to output. If the microcontroller is connected properly to the LED matrix, the synchSM should display a demo on the LED matrix where a single illuminated LED scrolls from left to right, top to bottom, then resets. The synchSM period should be at least 100 ms in order for the demo to be visible.
//--------------------------------------
// LED Matrix Demo SynchSM
// Period: 100 ms
//-------------------------------------- enum Demo_States {shift};
int Demo_Tick(int state) {
// Local Variables
static unsigned char pattern = 0x80; // LED pattern - 0: LED off; 1: LED on static unsigned char row = 0xFE; // Row(s) displaying pattern.
// 0: display pattern on row
// 1: do NOT display pattern on row
// Transitions switch (state) {
case shift:
break;
default:
state = shift;
break;
}
// Actions
switch (state) {
case shift:
if (row == 0xEF && pattern == 0x01) { // Reset demo pattern = 0x80;
row = 0xFE;
} else if (pattern == 0x01) { // Move LED to start of next row pattern = 0x80;
row = (row << 1) | 0x01;
} else { // Shift LED one spot to the right on current row pattern = 1;
}
break;
default:
break;
}
PORTC = pattern; // Pattern to display
PORTD = row; // Row(s) displaying pattern return state;
}
Video Demonstration of Demo: http://youtu.be/EYp3C6MWEU8
Design a system where an illuminated row of the LED matrix can be shifted up or down based on button presses.
Criteria:
● Two buttons control the system: One button shifts the illuminated row up. The other button shifts the illuminated row down.
● The illuminated row cannot be shifted off of the matrix. (i.e. If the illuminated row reaches the top of the LED matrix, if the “up” button is pressed again, the illuminated row will remain at the top of the LED matrix.)
Video Demonstration: http://youtu.be/DdK-x-z_xD8
Exercise 2 -- Shifting Columns
Design a system where an illuminated column of the LED matrix can be shifted left or right based on a button press.
Criteria:
● Two buttons control the system: Once button shifts the illuminated column right.
The other button shifts the illuminated column left.
● The illuminated column cannot be shifted off of the LED matrix (i.e. if the illuminated column reaches the far left side of the LED matrix, if the “left” button is pressed again, the illuminated column remains at the far left of the LED matrix.)
Video Demonstration: http://youtu.be/tF-ieEPy76Q
Exercise 3 -- Displaying a Rectangle
Design a system where a 3x4 hollow rectangle is displayed in the center of the LED
matrix like the photo below: Note: The varying brightness of the LEDs is only present in the photo. The completed exercise will not have varying brightness.
Hints:
● Since only one row pattern can be displayed on the LED matrix at a time, to display the rectangle, different patterns need to be displayed at different times
● Every one ms, update the pattern to be displayed and the row that the pattern will be displayed on.
● Use two arrays to store relevant data for the square. One array stores the patterns for each row. The other array stores the row that displays the pattern.
● Ground only one row at a time
Exercise 4 -- Shifting a Hollow Rectangle
Expand upon exercise 3 of the lab by introducing four buttons that control the position of the hollow rectangle.
Criteria:
● One button shifts the rectangle up
● One button shifts the rectangle down
● The other two buttons shift the rectangle left or right
● The rectangle cannot be shifted off of the LED matrix
Hints:
● Use two synchSMs. One synchSM controls the pattern displayed on the LED
matrix. The other synchSM monitors button presses.
Video Demonstration: http://youtu.be/Jpgkrmy_IZM
Exercise 5 (challenge) -- Adding Shift Registers
Repeat exercise 4 of the lab by using shift registers instead of directly wiring the microcontroller to the LED matrix.
Each person must submit their .c source files according to instructions in the Lab submission guidelines.
