Pic based Wind Speed meter

[BobEdge]

You could use the internal timer of the PIC to measure the time between pulses. I have done something similar to measure the frequency of an AC supply.

define OSC 40
INCLUDE "DT_INTS-18.bas"     ' Base Interrupt System
INCLUDE "ReEnterPBP-18.bas"     ' Include if using PBP interrupts

'set up timer 
T0CON = %00000001 '1/4 prescale fosc/4 not running (40MHz)
TMR0H = 0  ;Clear registers
TMR0L = 0

ASM
INT_LIST  macro    ;  IntSource,  Label,   Type, ResetFlag?
        INT_Handler    INT0_INT,  _ZERO,   PBP,  yes
    endm
    INT_CREATE               ; Creates the interrupt processor
ENDASM

@   INT_ENABLE   INT0_INT     ; enable external (INT) interrupts

goto start

ZERO: 'we have just detected zero cross signal.
'first job is to sort out the timer
@ bcf T0CON,TMR0ON ; Switch off timer
period.lowbyte = TMR0L  'Record Result
period.highbyte = TMR0H
@ clrf TMR0H  ; Reset registers to zero
@ clrf TMR0L
@ bsf T0CON,TMR0ON  ;Start timer
period = (period / 5) * 2  'Gives period value in microseconds
@ INT_RETURN

start:
'wait for interrupt to happen
goto start

END

You dont need to use interrupts either just a loop waiting for your input signal. In fact not using interrupts might be better. You could sort out your calculations and displaying the result without worrying about being interrupted.

You would need to set up the timer to give a useable range. I use the "PIC Timer Calculator" to do this, it makes things much easier.
You may need more than one pulse per revolution to give results at low wind speeds.

You may need to use the timer interrupt to flag if the timer has overflowed (got to 65535 & started counting again from zero) otherwise in very low winds you may not get a pulse before overflow, & the results would be wrong. If you get a timer overflow interrupt then you can say that the wind speed is zero.

http://pic-timer-calculator.software.informer.com/
http://darreltaylor.com/DT_INTS-18/home.html

Ofcourse this is all more complicated than using pulsein. But It is sometimes good to play around with more complex answers. It is the only way to learn new things. One month ago I knew nothing about using timers or Interrupts. Now it is second nature, and I wonder how I managed to get by without them.

Regards
Bob.

[Bobbo_ZA]

Hi Bob,

I totally agree, I have been playing with the manual AD routines and find it much more stable than the ADCIN function ,:-), the only question is which 18F to use, currently i have a 16F876A with a LCD connected and would like to connect some temp sensors and perhaps another pressure sensor, so im not 100% sure which 18F chip would be better suited. Any advice?

Kind Regards
Rob

[BobEdge]

Hi Rob,

That was written for a 18F1220 18 pin device. I also use 18F2420 28 pin, and 18F4550 40 pin. It depends which of the internal peripherals you want to use. Microchip have a chip selector tool on their site. You tell it what you need, and it will sugest which chips are suitable. Though it did not work last time I tried, but that was probably due to our totally slow, & unreliable internet at work.

I love how you can get clock speeds of 40 or 48MHZ using 10 or 20MHZ resonator, and using the HS PLL Enabled option. You can pretty much ignore how long calculations etc. take. It's so fast that it usualy makes no difference to your results.

The only things that get in the way are LCD, EEPROM, or serial comms, etc that always take a long time.

Regards
Bob.

[Bobbo_ZA]

Hi All,

Been a slow coding month, although I have been thinking and reading on how to do it, think i have settled on a disk option using a Phototransistor and counting the triggers every 1.5s using something like:

Count PORTB.2,1500,RPM

Depending on the number of gaps in the disk i can then do the maths to calculate the RPM and then tweak it / calibrate it to give me a rough wind speed, :-).

Going to start working on the mechanical parts of it this week and will post pictures and code once its done, :-)

[Bobbo_ZA]

Hi All,

Well, the count didn’t work as expected, seems the count function will only work for >100-150 rpm measurements, :-(. Even an event measured in 1 second, multiplied out the LCD reads it as 60rpm, ;-(

So far my code is as follows:

INCLUDE "DT_INTS-14.bas"     ' Base Interrupt System
INCLUDE "ReEnterPBP.bas"     ' Include if using PBP interrupts
INCLUDE "Elapsed_INT.bas"    ' Elapsed Timer Routines
DEFINE OSC 4 '4 MHz Osc
DEFINE LCD_COMMANDUS 2000
DEFINE ADC_BITS 10
DEFINE ADC_CLOCK 3
DEFINE ADC_SAMPLEUS 10
T1CON = %00000000 '1:1 Prescaler
TMR1H = 0  ;Clear registers
TMR1L = 0

TRISB = %00000001 'Set PortB.0 as input for Hall sensor
ADCON0 = %11100001
ADCON1 = %10000000  'Right Justify, VDD as vref
Hall var word 'VAR for hall sensor
Period var word
P1 var word
W2 var word  

ASM
INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
        INT_Handler    INT_INT,  _HallCount,   PBP,  yes
   ;     INT_Handler   TMR0_INT,  _TimePeriod,   PBP,  yes
        INT_Handler   TMR1_INT,  _ClockCount,   PBP,  yes
    endm
    INT_CREATE               ; Creates the interrupt processor
ENDASM
OPTION_REG = OPTION_REG & $80 | 1  ; Set TMR0 Prescaler to 256, leave RBPU alone
@    INT_ENABLE   INT_INT     ; enable external (INT) interrupts
'@    INT_ENABLE  TMR0_INT     ; enable Timer 0 interrupts
@    INT_ENABLE  TMR1_INT     ; Enable Timer 1 Interrupts  
wsave   VAR BYTE    $20     SYSTEM      ' location for W if in bank0
'wsave   VAR BYTE    $70     SYSTEM      ' alternate save location for W 
GOSUB ResetTime              ' Reset Time to  0d-00:00:00.00
GOSUB StartTimer             ' Start the Elapsed Timer
Main:
    IF SecondsChanged = 1 THEN  
       SecondsChanged = 0
       LCDOUT $FE,$C0, DEC Days,"d-",DEC2 Hours,":",DEC2 Minutes,":",DEC2 Seconds
    ENDIF
    LCDOut $FE, $80, "Period = ", DEC P1 DIG 3, DEC P1 DIG 2, dec P1 dig 3
GOTO Main
'---[INT - interrupt]---------------------------------------------------    
HallCount:  
         @ bcf T1CON,TMR1ON ; Switch off timer
        period.lowbyte = TMR1L  'Record Result
        period.highbyte = TMR1H
@ clrf TMR1H  ; Reset registers to zero
@ clrf TMR1L
@ bsf T1CON,TMR1ON  ;Start timer
period = (period / 5) * 2  'Gives period value in microseconds
p1 = period
@ INT_RETURN

I have left in the timer interupt running as it shows that the pic is running for now.

The output to the LCD now changes depending on the speed of the rotations, however I'm not sure if my prescaler is setup right (4mhz osc) and if the calc to get the microseconds is correct for my osc (thanks BobEdge).

[Bobbo_ZA]

One correction to the code, the hall sensor is on RB0 not in PortB.0.

RB0 is pulled high and the hall sensor pulls it low when the magnet passes (would like to still change this around but assume it wont make a difference except to power consumption).

[Bobbo_ZA]

Still stumped with the maths to try get the numbers is giving me into a usable number, anyone that can advise?

ALso, does anyone have any examples of where / how to capture the TMR overflow?