Guide on flow sensor application

[HenrikOlsson]

If it counts the pulses properly then I guess you're doing it right. However, doing it this way is probably not the best when you're trying to get more sensors in but more on that later.

If you look at the product page for the sensor there's a diagram showing the output frequency as a function of the flowrate. The output seems pretty linear (as you'd expect) with 4.5Hz/l/min.
So if you count pulses for on second and divide the result by 4.5 you have your flowrate in litres/minute.

For multiple sensors I'd set up a timer interrupt and poll all inputs in one go. Compare this state to the previous one to see if any input changed. Since the dutycycle of sensor output is 50% you can get twice the resolution (if needed) by counting both the positive and negativ going edges of the signal but then you'd need to poll the inputs twice as fast to guarantee not missing any pulses. It's going to be kind of like reading incremental encoders (lots of examples floating around here) but without the need to determine direction.

Nice hardware setup!

/Henrik.

[HenrikOlsson]

Hi,
I spent some time on this and here's what I came up with. It counts four sensors on PortC.0-3 using a timer based interrupt, polling the inputs at 250Hz. It counts both rising and falling edges effectively doubling the resolution and calculates the flowrate. Hope it's of some use.

'****************************************************************
'*  Name    : Flowrate.PBP                                      *
'*  Author  : Henrik Olsson                                     *
'*  Notice  : Copyright (c) 2011 Henrik Olsson 2010             *
'*          : No Rights Reserved                                *
'*  Date    : 2013-03-10                                        *
'*  Version : 1.0                                               *
'*  Notes   : Written for tacbanon.                             *
'*          : Counts pulses from four flow sensors connected    *
'*          : to the lower four bits of PortC and calculates    *
'*          : the flowrate based on 4.5Hz/l/min.                *
'*          : Program requires TMR1 interrupt to exectute at    *
'*          : 250Hz. Set TmrReload constant to correct value:   *
'*          : 61543 for 4MHz                                    *
'*          : 57543 for 8MHz                                    *
'*          : 45543 for 20MHz                                   *
'*          :  1543 for 64MHz                                   *
'*          : Tweak if neccesary                                *
'*          :                                                   *
'*          : Development board used: AMICUS18 platform @64MHz  *
'*          : Change hardware setup to match acutal hardware!   *
'****************************************************************
DEFINE OSC 64
DEFINE LOADER_USED 1                    ' We're using a bootloader.
DEFINE HSER_RCSTA 90h                   ' Enable serial port & continuous receive
DEFINE HSER_TXSTA 24h                   ' Enable transmit, BRGH = 1
DEFINE HSER_CLROERR 1                   ' Clear overflow automatically
DEFINE HSER_SPBRG 138                   ' 115200 Baud @ 64MHz, -0,08%

INCLUDE "DT_INTS-18.bas"                ' Include Darrel Taylors interrupt processing routines
INCLUDE "ReEnterPBP-18.bas"

ASM
INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
        INT_Handler   TMR1_INT,  _PollInputs,   PBP,  yes
    endm
    INT_CREATE              ; Creates the interrupt processor
ENDASM


' Create an alias to the TIMER1 register so we can access it as a word.
' Make sure RD16 is disabled.
@Timer1 = TMR1L
Timer1  VAR  WORD EXT

TMR1_ON VAR T1CON.0                     ' Alias to the TMR1ON bit

SensorCount Var BYTE[4]                 ' Count 4 sensors
FlowRate VAR BYTE[4]                    ' Flow rate for 4 sensors
SensorState VAR BYTE                    ' Stores current state of inputs.
PreviousState VAR BYTE                  ' Used to determine if inouts has changed state.
ISRCount VAR WORD                       ' Used to keep time based on number of interrupts
i VAR byte                              ' General purpose index variable
j VAR BYTE                              ' General purpose index variable
DataReady VAR BIT

TmrReload CON 1543                      ' 250Hz, 1:1 @64MHz

CLEAR

SPBRGH = 0
BAUDCON.3 = 1                           ' Enable 16 bit baudrate generator
TRISB = %00000000                       ' PortB.0 are all outputs
TRISC = %10001111                       ' Sensor inputs on PortC.0-3, RX/TX on PortC.7/PortC.6

Timer1 = TmrReload                      ' Preload the timer for 250Hz interrupt
TMR1_ON = 1                             ' Start the timer and....

@ INT_ENABLE TMR1_INT                   ; ....enable the interrupt

HSEROUT["Program start",13]

Main:
    If DataReady = 1 THEN               ' ISR sets this flag when data new data is avialble
        DataReady = 0                   ' Clear the flag
        HSEROUT["Flowrate: "]
        For j = 0 to 3

            ' The ISR calculate the flow rate in units of 0.1 litres per minute.
            HSEROUT[DEC FlowRate[j] / 10, ".", DEC FlowRate[j] // 10, "l/min."]
            
            If j = 3 THEN
                HSEROUT[13]
            ELSE
                HSEROUT[" - "]
            ENDIF
        
        NEXT
    ENDIF
Goto Main


' ------------- [Interrupt service routine for Timer1 interrupt] ---------------
' Designed to be executed at 250Hz. Make sure to change the TmrReload constant
' to match the actual clock frequency of the PIC.
 
PollInputs:
    TMR1_ON = 0                         ' Stop timer
    Timer1 = Timer1 + TmrReload         ' Reload timer, account for latency
    TMR1_ON = 1                         ' Restart timer  
    'Toggle PortB.0                      ' Used to verify interrupt frequency
    
    SensorState = PortC & %00001111     ' Get state of inputs.
  

  ' Iterate thru the four sensor inputs and determine if anyone has changed
  ' state since last interrupt. If so, increment the count for that sensor.
    For i = 0 to 3
        If SensorState.0[i] XOR PreviousState.0[i] = 1 THEN
            SensorCount[i] = SensorCount[i] + 1
        ENDIF
    NEXT

  
    PreviousState = SensorState         ' Store current state so we have something to compare with.

  
    ' To get some resolution we update the flowrate and volume at a rate of
    ' 0.5Hz based on the 250Hz interrupt frequency. The output frequency of
    ' the sensor is 4.5Hz/l/min, we're counting both rising and falling edges
    ' so we're getting 9 counts/l/min per second. We're counting for 2 seconds
    ' so we're going to divide by 1.8 to get the flow in units of 0.1 l/min
    
    ISRCount = ISRCount + 1
    If ISRCount = 499 THEN               ' 500 interrupts = 2 seconds.
        ISRCount = 0
        DataReady = 1
        For i = 0 to 3
            FlowRate[i] = SensorCount[i] ** 36409
            SensorCount[i] = 0
        NEXT
    ENDIF
@ INT_RETURN

/Henrik.

[tacbanon]

Hi,
I spent some time on this and here's what I came up with. It counts four sensors on PortC.0-3 using a timer based interrupt, polling the inputs at 250Hz. It counts both rising and falling edges effectively doubling the resolution and calculates the flowrate. Hope it's of some use.
/Henrik.

WOW Henrik...Thank You! I know it would take for me another week(s) to get this application running and probably thinking of another path to make it easier for me...but this is just so great (save me lot of precious time )...I will work on it, and feed back you later.

Kind regards,
tacbanon