Flow sensors produce pulses as liquids flow through them. Suppose that fuel flow and consumption needs to be measured in a system. This is accomplished by using a flow sensor such as the Gems FT-110 flow sensor. This device produces (model 173934) 8300 pulses per gallon of flow. The measurable flow rate is from .07 to 5.3 gallon per minute. Figure 7-30 illustrates the connection of this flow sensor to the microcontroller. This is a very simple device to interface that requires a single pull-up resistor and three wires.
EXAMPLE 7-21
/*
* Flow example written for a PIC18F1220
*/
#include <p18cxxx.h>
#include <timers.h>
/* Set configuration bits
* - set HS oscillator
* - disable watchdog timer
* - disable low voltage programming
* - disable brownout reset
* - enable master clear
*/
#pragma config OSC = HS
#pragma config WDT = OFF
#pragma config LVP = OFF
#pragma config BOR = OFF
#pragma config MCLRE = ON
void MyHighInt(void); // prototypes for interrupts
#pragma interrupt MyHighInt // MyHighInt is an interrupt
#pragma code high_vector=0x08 // high_vector is the vector at 0x08
void high_vector(void)
{
_asm GOTO MyHighInt _endasm
}
// data memory data
float flowRate;
// high prioity interrupt
#pragma code
void Timer1(void) // every 1/10 of a second
{
PIR1bits.TMR1IF = 0; // reenable Timer 1
WriteTimer1( 5303 );
flowRate = ReadTimer0() * 10.0 * 60 / 8300;
WriteTimer0( 0 ); // reset count
}
void MyHighInt(void)
{
if ( PIR1bits.TMR1IF == 1 )
Timer1();
}
// main program
void main (void)
{
ADCON1 = 0x0f; // all port pins digital
TRISA = 0x10; // Port A programmed
WriteTimer0( 0 ); // Timer 0 to 0
OpenTimer0(TIMER_INT_OFF & // Timer 0 interrupt on
T0_16BIT & // Timer 0 is 16-bits
T0_SOURCE_EXT & // Timer 0 clock is RA4
T0_EDGE_FALL & // pin RA4 negative edge
T0_PS_1_1 ); // Timer 0 prescaler is 1
WriteTimer1( 5303 ); // Timer 1 to 5303
OpenTimer1( TIMER_INT_ON & // Timer 1 interrupt on
T1_16BIT_RW & // Timer 1 is 16 bits
T1_SOURCE_INT & // Timer 1 clock is internal
T1_PS_1_8 & // Timer 1 prescaler is 8
T1_OSC1EN_OFF );
RCONbits.IPEN = 1; // IPEN = 1
INTCONbits.GIEH = 1; // enable high priority interrupts
// do other stuff here
}