Question

I have a project to program a microcontroller PIC18F, I have to connect a switching circuit to the microcontroller board, this switching circuit has an electric lock and a buzzer to be connected to it.

The lock is initially powered. It is supposed that when I send ‘1’, the buzzer will be powered with a square wave and the lock will be powered off. When it receives ‘0’, the buzzer will be switched off without powering the lock again. When it receives ‘2’ the lock should be powered but if the buzzer was unpowered before, it should not be powered again.

My confusion is in the last part. When I send ‘2’ via the hyperterminal, and I sent ‘0’ before it, the buzzer is powered again.

Here is the code,

void buzzertest();
char uart_rd;
int buzzer;
void main() {
TRISB=0X00;
PORTB=0x00;
RB5_bit = 0xFF;                  //lock  open
UART1_Init(9600);               // Initialize UART module at 9600 bps
while (1) {                     // Endless loop
 if (UART1_Data_Ready())       // If data is received,
 {
    buzzer=1;
    uart_rd = UART1_Read();     // read the received data,
    if(uart_rd =='1') {
       RB5_bit = 0x00;  //lock closed
       buzzertest();
     }
     if(uart_rd =='0' ){   //disable buzzer
        RB1_bit = 0x00;   //buzzer
        buzzer=0;
       }//end if
      buzzer=0;

      if(uart_rd =='2'){   //disable lock
        RB5_bit=0xFF;
        if(buzzer!=1){
            buzzertest();
         }
       }//end if
     } //end outer if
    } //end while
}//end main
void buzzertest(){
 while(1){
  RB1_bit = 0xFF;  //buzzer
  Delay_ms(1000);
  RB1_bit = 0x00; //buzzer
  Delay_ms(1000);
  if (UART1_Data_Ready())
  break;
 }//end while loop
}

Can please anyone help me solving this?

Answer 1

You’re setting buzzer to 0 outside the if(uart_rd='0') block. So when you come to the if(uart_rd='2') block, buzzer is always 0 and so the if(buzzer!=1) block is always called.

Have you tried stepping through this with a debugger? It would show up this kind of thing easily. You could also change those if blocks either to a switch statement or a series of if / else if statements to avoid these sorts of issues.