Ibrahim Dogan - Advanced PIC Microcontroller Projects in C

Figure 6.6: Block diagram of the project

As shown in Figure 6.7, the LEDs are organized such that when they turn ON, they indicate numbers as on a real dice. Operation of the project is as follows: The LEDs are all OFF to indicate that the system is ready to generate a new number. Pressing the switch generates a random number between 1 and 6 which is displayed on the LEDs for 3 seconds. After 3 seconds the LEDs turn OFF again.

Figure 6.7: LED dice

The circuit diagram of the project is shown in Figure 6.8. Seven LEDs representing the faces of a dice are connected to PORTC of a PIC18F452 microcontroller in current sourcing mode using 290-ohm current limiting resistors. A push-button switch is connected to bit 0 of PORTB (RB0) using a pull-up resistor. The microcontroller is operated from a 4MHz resonator connected between pins OSC1 and OSC2. The microcontroller is powered from a +9V battery, and a 78L05-type voltage regulator IC is used to obtain the +5V supply required for the microcontroller.

Figure 6.8: Circuit diagram of the project

The operation of the project is described in PDL in Figure 6.9. At the beginning of the program PORTC pins are configured as outputs and bit 0 of PORTB (RB0) is configured as input. The program then executes in a loop continuously and increments a variable between 1 and 6. The state of the push-button switch is checked and when the switch is pressed (switch output at logic 0), the current number is sent to the LEDs. A simple array is used to find out the LEDs to be turned ON corresponding to the dice number.

START

Create DICE table

Configure PORTC as outputs

Configure RB0 as input

Set J = 1

DO FOREVER

IF button pressed THEN

Get LED pattern from DICE table

Turn ON required LEDs

Wait 3 seconds

Set J = 0

Turn OFF all LEDs

ENDIF

Increment J

IF J = 7 THEN

Set J = 1

ENDIF

ENDDO

END

Figure 6.9: PDL of the project

Table 6.1 gives the relationship between a dice number and the corresponding LEDs to be turned ON to imitate the faces of a real dice. For example, to display number 1 (i.e., only the middle LED is ON), we have to turn on D4. Similarly, to display number 4, the LEDs to turn ON are D1, D3, D5, and D7.

Table 6.1: Dice number and LEDs to be turned ON

The relationship between the required number and the data to be sent to PORTC to turn on the correct LEDs is given in Table 6.2. For example, to display dice number 2, we have to send hexadecimal 0x22 to PORTC. Similarly, to display number 5, we have to send hexadecimal 0x5D to PORTC, and so on.

Table 6.2: Required number and PORTC data

The program is called LED2.C, and the program listing is given in Figure 6.10. At the beginning of the program Switch is defined as bit 0 of PORTB, and Pressed is defined as 0. The relationships between the dice numbers and the LEDs to be turned on are stored in an array called DICE . Variable J is used as the dice number. Variable Pattern is the data sent to the LEDs. Program then enters an endless for loop where the value of variable J is incremented very fast between 1 and 6. When the push-button switch is pressed, the LED pattern corresponding to the current value of J is read from the array and sent to the LEDs. The LEDs remain in this state for 3 seconds (using function Delay_ms with the argument set to 3000ms), after which they all turn OFF. The system is then ready to generate a new dice number.

/*****************************************************************************

SIMPLE DICE

===========

In this project 7 LEDs are connected to PORTC of a PIC18F452 microcontroller

and the microcontroller is operated from a 4MHz resonator. The LEDs are

organized as the faces of a real dice. When a push-button switch connected to

RB0 is pressed a dice pattern is displayed on the LEDs. The display remains in

this state for 3 seconds and after this period the LEDs all turn OFF to

indicate that the system is ready for the button to be pressed again.

Author: Dogan Ibrahim

Date: July 2007

File: LED2.C

*****************************************************************************/

#define Switch PORTB.F0

#define Pressed 0

void main() {

unsigned char J = 1;

unsigned char Pattern;

unsigned char DICE[] = {0,0x08,0x22,0x2A,0x55,0x5D,0x77};

TRISC = 0; // PORTC outputs

TRISB = 1; // RB0 input

PORTC = 0; // Turn OFF all LEDs

for(;;) // Endless loop

{

if(Switch == Pressed) // Is switch pressed ?

{

Pattern = DICE[J]; // Get LED pattern

PORTC = Pattern; // Turn on LEDs

Delay_ms(3000); // Delay 3 second

PORTC = 0; // Turn OFF all LEDs

J = 0; // Initialize J

}

J++; // Increment J

if (J == 7) J = 1; // Back to 1 if > 6

}

}

Figure 6.10: Program listing

In the preceding project the value of variable J changes very fast among the numbers between 1 and 6, so we can say that the numbers generated are random (i.e., new numbers do not depend on the previous numbers).

A pseudorandom number generator function can also be used to generate the dice numbers. The modified program listing is shown in Figure 6.11. In this program a function called Number generates the dice numbers. The function receives the upper limit of the numbers to be generated (6 in this example) and also a seed value which defines the number set to be generated. In this example, the seed is set to 1. Every time the function is called, a number between 1 and 6 is generated.