Rackley mentioned some legitimate points about resolution and timing when it involves engines that have multiple sensors that create a quantity of pulse per engine RPM. http://www.mikroe.com/forum/viewtopic.php?p=70751#70751
This program can help address his points and actually provide a simple solution. Read my comments inside of the code and see how this new approach can provide an alternate solution, while changing very little the overall concept of using the CCP input pin to catch signals and calculate RPM.
Code: Select all
program RPM_TACH2_CCP
' ***********************************************
' **** ANOTHER TACHOMETER DEMO USING THE
' **** THE PIC's CCP MODULE
' **** RANGE is 229 to 58,000 RPM
' **** SHOWS RPM RESULT ON CHARACTER LCD
' ***********************************************
' ***********************************************
' **** Program by Warren Schroeder March 18,2008
' **** Tach Demo Using 18F452 @ 8 MHz
' **** mikroBASIC 6.0
'************************************************
'************************************************
' **** Timer1 Prescaler=0 Ticks @ 0.5us
' **** Timer1 Prescaler=2 Ticks @ 1.0us
' **** Timer1 Prescaler=4 Ticks @ 2.0us
' **** Timer1 Prescaler=8 Ticks @ 4.0us
' ************************************************
' *******************************************************************************
'***** FURTHER NOTES ON THIS DEMONSTRATION CODE:
'***** Using the CCP Capture Mode, this code does not care to read Timer1 at every
'***** CCP Input Pin pulse and interrupt.
'***** Instead, it will capture all pulses, accumulate
'***** them, and then average them over a period of time.
'***** This averaging can produce some nice results for displaying finer RPM output
'***** especially at low RPM in some special cases.
'*****
'***** This program catches all input pulses over the full timing count of Timer1,
'***** or until Timer1 rolls over to 0.
'***** Timer1 sets PIR1.TMR1IF when rollover (overflow) occurs and is
'***** very easy to test. Timer1 below will rollover every 262ms.
'***** 262ms is equivalent to 229 RPM, if only 1 pulse was counted.
'***** From this we can create some simple
'***** RPM calculations for other pulse count totals. The formula being:
'***** pulsecount * 229, with 229 RPM being the best per pulse resolution
'*****
'***** Let's take this a step further. Assume that you have an engine with a rotor
'***** that has 4 Hall Effect sensors. This means that 1 RPM creates 4 pulses.
'***** RPM calculation over 262ms would look like this:
'***** pulsecount * 229 / 4, with 57 RPM being the best per pulse resolution
'***** Adding these extra pulses can create a finer more accurate RPM output.
'********************************************************************************
CONST
CAPTURE_FALLINGEDGE as byte = 4
CAPTURE_RISINGEDGE as byte = 5
T1_Prescale_0 as byte = 0
T1_Prescale_2 as byte = 16
T1_Prescale_4 as byte = 32
T1_Prescale_8 as byte = 48
RPMBase as byte = 229
DIM
REV as Byte ' total pulse counts
RPMCalc as Byte
RPMVal as Word
RPMStr as String[5]
Sub Procedure INTERRUPT()
If PIR1.CCP1IF = 1 Then ' input pulse counter, ignore CCPR1
inc(REV) ' accumulate pulses
PIR1.CCP1IF = 0 ' prepare for next CCP interrupt
End If
If PIR1.TMR1IF = 1 Then ' test Timer1 for overflow
' **** If Timer1 Overflows = 65536 x 4us = 262ms = 229 RPM
RPMCalc = REV ' save pulsecounts for calculations below
REV = 0 ' clear pulsecounter
PIR1.TMR1IF = 0 ' clear Timer1 Overflow Flag
End If
End Sub
Sub Procedure CCP_SETUP()
INTCON = 192 ' Enable Global & Peripheral Interrupts
T1CON = T1_Prescale_8 ' Ticks every 4us
TRISC.2 = 1 ' CCP1 pin is input
CCP1CON = CAPTURE_RISINGEDGE ' catch every 4th rising edge
PIE1.CCP1IE = 1 ' enable CCP1 Interrupt
PIR1.CCP1IF = 0 ' Clear CCP1 INTERRUPT Flag
TMR1H = 0 ' reset Timer1
TMR1L = 0
PIR1.TMR1IF = 0 ' Timer1 Overflow Flag Cleared
T1CON.TMR1ON = 1 ' Timer1 Running
end sub
Sub Procedure GENERAL_INIT()
ADCON1 = 6 ' disable analogs
LATA = 0
LATB = 0
LATC = 0
LATD = 0
LATE = 0
TRISA = 0
TRISB = 0
TRISC = 0
TRISD = 0
TRISE = 0
end sub
main:
General_Init()
CCP_Setup()
LCD_INIT(PORTB)
LCD_CMD(LCD_CURSOR_OFF)
LCD_OUT(1,6, " RPM")
REV = 0
RPMCalc = 0
Do
If RPMCalc <> 0 Then ' pulses occurred and make RPM Calculation
RPMVal = RPMCalc * RPMBase
RPMCalc = 0 ' clear for next Timer1 period
End If
Delay_ms(50) ' update LCD every 50ms
WordToStr(RPMVal, RPMStr) ' convert for LCD
LCD_OUT(1, 1, RPMStr) ' print to LCD
Loop Until 0=1
end.
