On Sun, Aug 16, 2009 at 4:46 PM, Robert Bullock<bobb@prostyle.com> wrote:
>
> Ok, I should have read further regarding the duty period, however, I still
> would not rule out using a hall effect sensor.
> The continuous duty ones typically draw 2.5 to 5mA and that in itself is =
not
> too bad for a
> battery powered application that your making yourself. However, it isn=92t
> great either, but there
> is a fairly simple solution to that too. After you have sensed a couple of
> rotations, you could
> start to shut off the hall effect sensor until, say, 80% of the previous
> periods time frame is
> expired.

Wouldn't this scheme lock to subharmonics of the actual period?  For
example, the wheel rotates twice a second, but the sensor might lock
on to once per second and read a speed of half the actual speed.

And 1 mA is a *lot* of current for this.  There is no reason low-power
design is incompatible with hobby electronics.  There are no special
tools or techniques required for designing for low power.  Just read
the datasheet, use sleep mode, and measure the actual current draw
with a DMM.  Nothing tricky.

For solarwind, you should look at the AVR butterfly kit for this.  For
$20 you get a micro with bootloader and a decent LCD, and the battery
holder and other goodies are there too.   I know you write C, and
there is a good GCC port for AVR.

Regards,
Mark
markrages@gmail
-- =

Mark Rages, Engineer
Midwest Telecine LLC
markrages@midwesttelecine.com

-- =

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