Pic based Wind Speed meter

[Bobbo_ZA]

Were you interfacing the Memsic to a pic or into something like an Aurdino / Propeller / Stamp? I've used the 3-axis versions quite a bit in my Tri-copter build, but was hoping to interface to a PIC, for one thing they are a lot cheaper in SA and also easier to come by.

[Amoque]

Were you interfacing the Memsic to a pic or into something like an Aurdino / Propeller / Stamp? I've used the 3-axis versions quite a bit in my Tri-copter build, but was hoping to interface to a PIC, for one thing they are a lot cheaper in SA and also easier to come by.

The output is a 100Hz PWM signal, easily read with any MCU that can measure a pulse. I'm new to PICs, but "Pulsein" seems like just the ticket. The link was only to show the Memsic; the data sheet is there as well.

[jetpr]

You Can use Hall Sensor
By read of North and South of the magnet it account 1 return for each turn of the shaft.

[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, :-)