/* 
* Project name: Contact less digital tachometer


 * Test configuration:

 MCU: PIC16F628A runs @ 4.0 MHz external crystal oscillator 
The common cathodes of the four seven segment dispalys are 
controlled by RA0, RA1, RA2 and RA3 
*/ 
//-------------- Function to Return mask for common cathode 7-seg. display 
unsigned short mask(unsigned short num) { 
 switch (num) { 
   case 0 : return 0x3F; 
   case 1 : return 0x06; 
   case 2 : return 0x5B; 
   case 3 : return 0x4F; 
   case 4 : return 0x66; 
   case 5 : return 0x6D; 
   case 6 : return 0x7D; 
   case 7 : return 0x07; 
   case 8 : return 0x7F; 
   case 9 : return 0x6F; 
 } //case end 
} 
sbit IR_Tx at RB7_bit; 
sbit DD0_Set at RA0_bit; 
sbit DD1_Set at RA1_bit; 
sbit DD2_Set at RA2_bit; 
sbit DD3_Set at RA3_bit; 
unsigned short i, DD0, DD1, DD2, DD3; 
unsigned int Sample1, Sample2, Sample3, RPM; 
void main() { 
TRISB = 0b00000000; // Set PORTB direction to be output 
TRISA = 0b00110000; // Set PORTA direction to be output 
PORTB = 0x00; // Turn OFF LEDs on PORTB 
CMCON = 7 ; // Disable comparators 
RPM = 0; // Initial Value of Counter 
OPTION_REG = 0b00111000; // TOCS=1 for Counter mode, PSA=1 for 1:1 
IR_Tx = 0; // Turn OFF IR 
do { 
DD0 = RPM%10; 
DD0 = mask(DD0); 
DD1 = (RPM/10)%10; 
DD1 = mask(DD1); 
DD2 = (RPM/100)%10; 
DD2 = mask(DD2); 
DD3 = (RPM/1000); 
DD3 = mask(DD3); 
for (i = 0; i<=100; i++) { 
PORTB = DD0; 
DD0_Set = 1; 
DD1_Set = 0; 
DD2_Set = 0; 
DD3_Set = 0; 
delay_ms(5); 
PORTB = DD1; 
DD0_Set = 0; 
DD1_Set = 1; 
DD2_Set = 0; 
DD3_Set = 0; 
delay_ms(5); 
PORTB = DD2; 
DD0_Set = 0; 
DD1_Set = 0; 
DD2_Set = 1; 
DD3_Set = 0; 
delay_ms(5); 
PORTB = DD3; 
DD0_Set = 0; 
DD1_Set = 0; 
DD2_Set = 0; 
DD3_Set = 1; 
delay_ms(5); 
} 
DD3_Set = 0; 
// First Sample 
TMR0=0; 
IR_Tx = 1; 
Delay_ms(1000); // Delay 1 Sec 
IR_Tx = 0; 
Sample1 = TMR0*60; 
// Second Sample 
TMR0=0; 
IR_Tx = 1; 
Delay_ms(1000); // Delay 1 Sec 
IR_Tx = 0; 
Sample2 = TMR0*60; 
// Third Sample 
TMR0=0; 
IR_Tx = 1; 
Delay_ms(1000); // Delay 1 Sec 
IR_Tx = 0; 
Sample3 = TMR0*60; 
RPM = Sample1 + Sample2 + Sample3; 
RPM = RPM/3; 
} while(1); // endless loop 
}