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Problem with C and PIC16F628A

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Andrei917

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Hi all, first I need to say I'm not good with microcontrollers, and I am building my second tesla coil, that is why I need a tachometer for the rotary spark gap RPM.

I started to look everywhere for a tachometer project, but I'm a bit limited on "money". I was trying to use PIC, because I can use pickit programmer at work. Then I found a code and schematics using PIC16F628A and 4 digit 7 segment display on the internet. Since I have this pic at work, my boss let me use it to test, if it works, then I will buy the parts.

I build the wiring as a lot of PIC projects:

RA0-3 ports control the digits
RB0-6 ports the segments
RA4 signal from IR transistor
RB7 turns on a IR led
MCRL goes to +5v
4MHz Crystal

Still the thing don't work. It shows 0000 when motor is off. If i turn on the motor, it show 8888, sometimes 8808, or some random segments that don't look like a number nor a letter.

I used this code from a blog. I found somewhere at this forum that a "break" comes after the case 0,1,2... lines, still it don't work.

Code C - [expand]
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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
}
 
Last edited by a moderator:

Hi, I read that thread, but there is no store selling PIC18F14k50 here. Only if I buy from US. I would but mail here is terrible, it will take 4-6 months to get the product. I will use optic IR led and transistor. The hall sensor needs a magnet, and I'm afraid if it will work properly will the very high voltage around.

Atmega is impossible right now, I can't buy the programmer, things are expensive here. The other project with PIC 18f452, maybe I can find that microcontroller around here, I was trying to use 7 segments display, which I can read from very far*, but if this one with 18f452 works, I will use LCD... *I can't stay close to the coil.

I have been trying to understand how to use C with PIC, but I'm not good with technical english vocabulary, actually google translate is helping me on this post heh. Maybe I can find a book in portuguese.

Well I have to think a bit about what I'm going to do, I can spend around 25$ this month... I almost got a chinese tachometer, but they only use 1 "pulse" / rotation, that is not very precise in low RPMs. This part of the code I could edit, to count more pulses/rotation, but their tachometer is probably code protected. My problem is the part where the code "talks" with PIC, the ports, LCD.
 
Last edited:

The designs discussed in the thread can be easily ported to the PIC16F series, there is no need to purchase a PIC18F device.

BigDog
 

I didn't knew that was possible. I will study how to do that. Thank you.
 

As long as the PIC provides the required feature or peripheral module utilized by the design/code, you should be able to port the source to a particular device.

BigDog
 

The first code shown works (sort of) but the delays cause the display to turn off and back on again on about a 3 second cycle.
 

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