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<div class="moz-cite-prefix">On 11/26/2013 02:38 PM, Charles
McClelland wrote:<br>
</div>
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cite="mid:7AEB4613-6A61-4F66-AA43-DB2A15BB026C@mcclellands.org"
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<div><span class="Apple-tab-span" style="white-space:pre"> </span>-
Changed from 18650 LiON batteries to 4 AA alkaline batteries in
series. Not sure if this is any better than 3 AA batteries so I
plan to test that next. Thoughts?</div>
</blockquote>
<br>
Turns out the SD interface uses an amazing amount of current to
write, perhaps 10 or 20 times the current the Mini's CPU is drawing.<br>
<br>
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<div><span class="Apple-tab-span" style="white-space:pre"> </span>-
Moved from 5V to 3.3V - this helped on two fronts. 1) The micro
SD card is a 3.3V device so I eliminated some components. and 2)
I was able to use the voltage regulator on the Pro Mini for more
of my battery pack’s useful life</div>
<div><span class="Apple-tab-span" style="white-space:pre"> </span>-
Put in a switch to turn off the LED - it turned out that the
indicator LED I was using for setup / testing was a major drain
- added a latching push button switch to turn it off for normal
use</div>
<div><br>
</div>
<div>4) Sleep mode - I played with this but was disappointed. It
turns out that the millis() count is stopped in all but the
lightest sleep mode. This was a real problem before I moved to
the real</div>
</blockquote>
<br>
If you don't need the clock chip's alarm feature you could program
the INT bar/SQW pin to put out a square wave and periodically wake
the cpu up with that. Another possibility is varying the CPU clock
speed between active periods.<br>
<br>
<blockquote
cite="mid:7AEB4613-6A61-4F66-AA43-DB2A15BB026C@mcclellands.org"
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<div>time clock but I could also not get the interrupt working
consistently with the piezo sensor (too transient a signal?).
May revisit but it looks like I hit my goal for battery life
without this step.</div>
<div><br>
</div>
<div>5) Sensor - I heard there was discussion about using an
accelerometer instead of a piezo for sensing movement. I would
be interested in this but have a concern about using a $10 for
the most exposed part of the system. I recently bought a lot of
10 piezos from eBay for $6 and my expectation is that this is
the component which will get the most wear and abuse. I am
looking at a few alternatives to the <a moz-do-not-send="true"
href="https://www.sparkfun.com/products/10293">basic piezo</a> -
a <a moz-do-not-send="true"
href="https://www.sparkfun.com/products/9196">larger version</a>,
one with a <a moz-do-not-send="true"
href="https://www.sparkfun.com/products/9197">mass attached</a> (as
I am looking for low frequency signal), and perhaps a <a
moz-do-not-send="true"
href="http://www.mouser.com/ProductDetail/Mountain-Switch/107-2009-EV/?qs=sGAEpiMZZMuRFIlaTiDGn6wXOgQixfplWXe4vgIGDyc=">vibration
switch</a> which could solve my interrupt problems. Would be
interested in any thoughts folks have on this.</div>
</blockquote>
My concern would be the second 10 piezos you get won't behave the
same way. Not that I have any idea whether there is a lot of
variability with these and how critical their performance is to your
application. But with an accelerometer chip something very
repeatable could be arranged and the sensitivity would be
programmable both in terms of the G range mapping to the output bits
and by filtering the samples. If you're intending to make your own
board the right number for an accelerometer cost should be $2-3
tops. <br>
<br>
It might be important to arrange to clamp the output of the piezo
transducer so it doesn't blow a transistor junction when the crystal
gets smacked hard. Notice that gas ignition gadgets are based on
striking a crystal and getting very high potentials to arc over. :-)<br>
<br>
-Pete<br>
<br>
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