how to read velocity from optical encoder using pic

[Ra]

Hi,
My project is relate with motor control and i use two motors, i try using pic18f2431 to capture the position and velocity but i can get only position.

Any one have a sample code to get velocity from pic18f2431 using interrupt qei and interupt port b?

code to capture the position is

#include <18F2431.h>
#fuses HS,NOWDT,NOPROTECT,NOLVP
#use delay(clock=20000000)
#use rs232(baud=9600, parity=N, Bits=8, xmit=PIN_C6, rcv=PIN_C7,stream=COM_1)
#BYTE QEICON=0xFB6 // quadrature configure
#bit QEICONDIR=0xFB6.5
#BYTE DFLTCON=0xF60 // quadrature noise filter configure
#BYTE CAP2BUFL=0xF66 // position counter
#BYTE CAP2BUFH=0xF67
#BYTE CAP3BUFL=0xF64 //max count
#BYTE CAP3BUFH=0xF65
#byte portb=0xF81
#bit bchanged=0xFF2.0
#use fast_io(B)
unsigned int16 quadhigh=0;
signed int32 position=0;

#int_rb
void myint(void) {
static int old;
static int new;
static int value;
new=portb;
value=new^old;
//'value', now has the bit set, which has changed
if (value & 0x10) {
//Here the low bit has changed
if (new & 0x10) {
//Here a rising edge on A
if (new & 0x20) --position;
else ++position;
}
else {
//Here a falling edge on A
if (new & 0x20) ++position;
else --position;
}
}
else {
//Here the high bit (B) must have changed
if (new & 0x20) {
//Here a rising edge on B
if (new & 0x10) ++position;
else --position;
}
else {
//Here a falling edge on B
if (new & 0x10) --position;
else ++position;
}
}
old=new;
bchanged=0;
#asm
RETFIE 1
#ENDASM
}

#int_IC2QEI
QuadRollover()
{
QEICONDIR?quadhigh++:quadhigh--;
}
void main(void) {
signed int32 position1=0;
signed int32 old_pos=0;
signed int32 lastpos=0;
position=0;
QEICON=24; // quad in x4 mode, resettable by maxcount
DFLTCON=49; // noise filter on QEA, QEB,, 1:2 clock
CAP3BUFL=0xFF; // set max count
CAP3BUFH=0xFF;
CAP2BUFL=0;
CAP2BUFH=0;
port_b_pullups(true);
setup_adc_ports(NO_ANALOGS);
setup_spi(FALSE);
set_tris_B(0x30);
enable_interrupts(INT_RB);
enable_interrupts(INT_IC2QEI);
enable_interrupts(global);
lastpos=position;
while (true) {
position1=(((int32)(quadhigh))<<16)+(CAP2BUFL+((int16) CAP2BUFH<<8));
if(lastpos!=position || old_pos!=position1){
lastpos=position;
old_pos=position1;
delay_ms(20);
printf("%ld %ld\n\r",lastpos*360/500/23,old_pos*360/500/23);

}

}
}

Thank you for your help.

[kender]

When your encoder provides an interrupt on each increment, so the velocity is 1/delta_t [clicks/sec], where delta_t is the time between the current interupt and the previous one. You need to set up one of the PIC's timers, which will generate delta_t. If your revolution rate is high enough, you can read the timer via get_timerX() and reset the timer at the end of your RB interrupt via set_timerX(0). If your revolution rate is not high enough, you'll need to count the interrupts in a global variable.

P.S. Please edit your original posting to add the code tags around your code.

[Guest]

Hi Kender,
Thank you very much for your reply. but I don't understant your explanation, Give me more detail about this if you have example code please give me.

Thank you.[/code]