Using CCP1 and CCP2 to measure instant fuel consumption

[srspinho]

Hello friends,

some time ago, I did a digital speedometer for my car using the following code to count pulses (written by Tim_B for Proton Basic)

==============================================

Define LCD_DREG PORTA
Define LCD_DBIT 0
Define LCD_RSREG PORTB
Define LCD_RSBIT 4
Define LCD_EREG PORTB
Define LCD_EBIT 5

REM Variables
TMR0_POSTCOUNT1 var WORD ' POSTSCALER COUNTERS
COUNT_RESULT var WORD ' THE RESULT OF THE COUNT
REFRESHED var BIT ' FLAG TO SAY COUNT REFRESHED

'-------------------------'
ON INTERRUPT GOTO PULSE_COUNT ' DEFINE WHERE TO JUMP TO ON AN INTERRUPT
'-------------------------'

GOTO INITIALIZE ' JUMP ALL INT CODE

'----- INTERRUPT CODE -------------------
Disable
PULSE_COUNT:
TMR0 = TMR0 + 7 ' RELOAD THE TIMER
TMR0_POSTCOUNT1 = TMR0_POSTCOUNT1 - 1
IF TMR0_POSTCOUNT1 = 0 THEN
TMR0_POSTCOUNT1 = 500 ' 1/4 sec (may need some adjust)
T1CON.0 = 0 ' TURN OFF THE TMR1
COUNT_RESULT.lowbyte = TMR1L ' GET THE COUNT
COUNT_RESULT.Highbyte = TMR1H ' GET THE COUNT
TMR1L = 0
TMR1H = 0
T1CON.0 = 1
REFRESHED = 1 ' SET FLAG TO SAY COUNT READ
ENDIF
INTCON.2 = 0 ' CLEAR INTTERUPT FLAG
Resume
enable ' RELOAD THE SYSTEM VARS
'------ END OF INTERRUPTS CODE ----------

'------ INTIALIzE ALL REGS --------------
INITIALIZE:

TMR0_POSTCOUNT1 = 500 ' INITIALZE THE POST SCALERS
OPTION_REG.0 = 0 ' SET THE PRESCALER TO 1:1
OPTION_REG.1 = 0
OPTION_REG.2 = 0
OPTION_REG.5 = 0 ' TMR0 CLOCK FROM MAIN OSC
OPTION_REG.3 = 0 ' IN THIS INSTANCE PRESCALER IS ASSINED TO TMR0
INTCON.2 = 0 ' CLEAR INTERRUPT FLAG
T1CON = %00000110
T1CON.0 = 1 ' TURN TIMER 1 ON
TMR0 = 7 ' LOAD THE TIMER
INTCON.5 = 1 ' ENABLE TMR0 INTERRUPTS
REFRESHED = 0 ' DONT MAKE FIRST READ UNTIL MAIN INT HAS OCCURED
INTCON.7 = 1 ' START THE WHOLE THING RUNNING
COUNT_RESULT = 0
pause 500
lcdout $FE,1



'------ MAIN CODE BELOW HERE -------------

LOOP:
IF REFRESHED = 1 THEN
lcdout $fe,1,$fe,2, "Freq = ", dec (COUNT_RESULT * 4) ' Show results in pulses / Sec
REFRESHED = 0 ' PREVENT A RE-READ UNTIL NEXT MAIN INTERRUPT
ENDIF
GOTO LOOP

END

===========================================

Well, I bought a new car (used, but newer than the other one). I had do modify a lot my circuit to make it working due to the Car´s Hall sensor strange bahavior. Now, it´s fixed.

But now, I would like to measure my instat fuel consumption, reading the Injector´s "on" time and the engine´s RPM (please, see http://www.eelkevisser.nl/fuel.htm )

I was reading the 16F877A datasheet and I noticed that CCP1 and CCP2 uses Timer1.

Is it possible to measure those two other parameters (engine´s RPM and Injector "on"-time) using the CCP1 and CCP2 without messing my interrupts ?

Sorry for my bad english !

Regards.

Sérgio

[Bruce]

Capture is not reliable with Timer1 in asynchronous counter mode. You're also
stopping & clearing Timer1 in your interrupt handler which would cause
problems with capture.

I would change to the 18F4431. This one has a Motion Feedback Module with
capture that uses Timer5, measures pulse widths or frequency, and it's really
easy to use.

The 18F4431 has everything you need.

[Johan]

Hi Bruce,

I am interested to use motion feedback module on 18F4431, could you please post sample code how to read the number of rotation ?

Thanks,

Johan

[srspinho]

Thanks Bruce !

I will check here were I live, if I can buy this device.

But, thank you for your advice !

Do you have tips on how to use the CCP4 and/or CCP5 on this device ?

Regards .

Sérgio

[Bruce]

Here's an example of measuring a 32kHz signal on RA2 with the Motion Feedback Capture. It's pretty simple to use.

DEFINE OSC 4
DEFINE DEBUG_REG PORTC
DEFINE DEBUG_BIT 6 
DEFINE DEBUG_BAUD 9600
DEFINE DEBUG_MODE 0 ' 1 = inverted, 0 = true

T1 VAR WORD
T2 VAR WORD
T3 VAR WORD

Capture VAR PIR3.1
False CON 0
True  CON 1

' auto time base reset, capture on rising to falling edge
    RiseToFall CON %01000111
' auto time base reset, capture on falling to rising edge
    FallToRise CON %01000110
' auto time base reset, frequency mode, capture on every rising edge
    Frequency  CON %01000101
  
    ANSEL0 = 0           ' All digital
    TRISA.2 = 1          ' Cap1 input pin (Capture input)
    INTCON = 0           ' Interrupts off
    TMR5H = 0            ' Clear high byte of TMR5 counter
    TMR5L = 0            ' Clear low byte
    T5CON = %00000001    ' prescale=1:1, int clock, TMR5=on

    GOTO Main
    
Trash: ' Trash 1st capture after capture mode changes
    Capture = False       ' Reset capture flag
    WHILE Capture = False ' Wait for capture
    WEND                  ' 
    Capture = False       ' Reset capture flag
    RETURN                ' Return 

Main:
    GOSUB LtoH
    GOSUB HtoL 
    GOSUB Freq
    PAUSE 500
    GOTO Main

LtoH:
    ' Capture on falling to rising edge
    CAP1CON = FallToRise 
    GOSUB Trash
    WHILE Capture = False 
    WEND
    T1.HighByte = CAP1BUFH ' high byte
    T1.LowByte = CAP1BUFL  ' low byte

    DEBUG "Low PW = ",DEC T1,"uS",13,10
    RETURN
    
HtoL:
    ' Capture on rising to falling edge
    CAP1CON = RiseToFall
    GOSUB Trash
    WHILE Capture = False
    WEND
    T2.HighByte = CAP1BUFH
    T2.LowByte = CAP1BUFL

    DEBUG "High PW = ",DEC T2,"uS",13,10
    RETURN
    
Freq:    
    ' Frequency measurement mode, capture every rising edge
    ' to measure period
    CAP1CON = Frequency
    GOSUB Trash
    WHILE Capture = False
    WEND
    T3.HighByte = CAP1BUFH
    T3.LowByte = CAP1BUFL

    DEBUG "Freq = 1/",DEC T3,"uS",13,10
    RETURN

    END

Returns;
High PW = 17uS
Low PW = 14uS
Freq = 1/31uS

This 18F series has a boat-load of nifty features. Check out how fast the A/D
is. Should be a killer PIC for robotics applications.

[srspinho]

Thank you very Much Bruce !

regards .

Sérgio