Hello community,

I'm attempting to implement a serial controlled relay driver using a PIC16F877A uC.

My circuit can be described in the next manner: A +12v input, a LM7805 for a net of +5v, a MAX232 for TTL signal conversion, PIC16F877A for serial communication and controlling the output port on which eight relays will be controlled. Each relay will power up a +12v strobe light at a time.

I have the schematic done but I'm struggling with the programming of the PIC, I have read several tutorials on using USART for serial communication an I have the following code:

// PIC16F877A Configuration Bit Settings
#include <xc.h>
// CONFIG0
#pragma config CP = OFF // Code protection OFF
#pragma config DEBUG = OFF // Debugger OFF
#pragma config WRT = OFF // Flash program memory write OFF
#pragma config CPD = OFF // Data EEPROM memory code protection OFF
#pragma config LVP = OFF // Low voltage In-circuit serial programming OFF
#pragma config BODEN = ON // Brown-out reset enable ON
#pragma config PWRTE = OFF // Power-up timer enable OFF
#pragma config WDTE = OFF // Watchdog timer enable OFF
#pragma config FOSC = HS // Oscillator HS : High speed crystal

#define STRLEN 12

volatile unsigned char t;
volatile unsigned char rcindex;
volatile unsigned char rcbuf[STRLEN];

void USART_init(void)
{
TXSTAbits.TXEN = 1; // enable transmitter
TXSTAbits.BRGH = 1; // high baud rate mode
RCSTAbits.CREN = 1; // enable continous receiving

// configure I/O pins
TRISCbits.TRISC7 = 1; // RX pin is input
TRISCbits.TRISC6 = 1; // TX pin is input (automatically configured)

SPBRG = 25; // set baud rate to 9600 baud (4MHz/(16*baudrate))-1

PIE1bits.RCIE = 1; // enable USART receive interrupt
RCSTAbits.SPEN = 1; // enable USART
}

void USART_putc(unsigned char c)
{
while (!TXSTAbits.TRMT); // wait until transmit shift register is empty
TXREG = c; // write character to TXREG and start transmission
}

void USART_puts(unsigned char *s)
{
while (*s)
{
USART_putc(*s); // send character pointed to by s
s++; // increase pointer location to the next character
}
}

int main(void)
{
USART_init();

USART_puts("Initialized!\n");

INTCONbits.PEIE = 1; // enable peripheral interrupts
INTCONbits.GIE = 1; // enable interrupts


TRISD = 0; //Define PORTD as output

while(1)
{
if (rcbuf == "relay1")
PORTBbits.RB0 =1;
}

return 0;
}

void interrupt ISR(void)
{
if (PIR1bits.RCIF) // check if receive interrupt has fired
{
t = RCREG; // read received character to buffer

// check if received character is not new line character
// and that maximum string length has not been reached
if ( (t != '\n') && (rcindex < STRLEN) )
{
rcbuf[rcindex] = t; // append received character to string
rcindex++; // increment string index
}
else
{
rcindex = 0; // reset string index
USART_puts(rcbuf); // echo received string
}

PIR1bits.RCIF = 0; // reset receive interrupt flag
}
}

Let's take a look at the main loop:

while(1)
{
if (rcbuf == "relay1")
PORTBbits.RB0 = 1;
}

Will this set RB0 to high when the string at rcbuff is relay1?

Any easier way of setting this up?

Thanks, any help will be greatly appreciated.

 

if (rcbuf == "relay1")

Learning some C would be helpful for you.

 

C will not compare strings directly. Use strcmp or strncmp which you will find in the libraries. These are described in Appendix A of the XC8 compiler User's Guide. You'll have to include string.h to use them.

Good luck.