Hi Richard,

At 13:08 20/02/97 -0800, you wrote:
>I'm in the process of designing/building an anemometer.  To measure
>the speed of the wind, I'm going to be counting the number of
>revolutions the shaft makes.
>
>My question is: can I just a timing loop approach to counting the
>number of revoultions or should I use a timing interrupt from a
>real-time clock?
>
>In other words, would this appoarch give me acceptable results:
>        For i = 1 to NumberOfLoops
>                if revolution detected then
>                        NoOfRevs = NoOfRevs + 1
>                endif
>        next i
>
>where I have computed the amount of time it takes to do the loop.  Or
>would I be better off if I do something like:
>
>        wait for timing interrupt
>        while no timing interrupt detected
>                if revolution detected then
>                        NoOfRevs = NoOfRevs + 1
>        wend


a far neater method is the following, using two timers in your PIC:

One of the timers is preloaded / prescaled such that it will generate an
interrupt every <n> ms. (input = OSC) This is your system's heartbeat.

Then to measure the number of revolutions, you start a counter that counts
the pulses read from the shaft (e.g. TMR1 in a 'C64). Depending on the pulse
frequency and the accuracy, you let it count for a certain time and read it
out.
The time is of course a multiple of the <n> ms heartbeat.

The <n> ms depends on your OSC frequency. To give you an example, using a
2.4576 MHz Xtal and some presacling, I get a 5 ms heartbeat. The interrupt
routine counts the heartbeats and every 200 beats (1 sec), it stops + reads
the 16 bit TMR1, writes it to some variable and clears the TMR1 and starts
it again.

Your main program only has to read the variable whenever it wants.

Jeroen

>
>Thanks in advance for you comments/suggestions/ideas,
>
>
>Richard Rosenheim
>rrose@accessnv.com
>
>
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