On Tue, 09 Oct 2007 16:22:17 GMT, Winston
wrote:

Don Foreman wrote:
On Mon, 08 Oct 2007 20:00:11 GMT, Winston
wrote:


steamer wrote:


--Looking for a solution to a little design problem. The situation
arises due to a firewood pile that's periodically infested with various
crawley vermin, which means that, before a log goes into the fireplace I
first pick it off the pile, then throw it onto the ground and watch the
little buggers scurry off, then pick it up a second time and take it to the
fireplace. What I'm thinking is I'll build a really heavy duty firewood rack
out of steel, then build something that lifts one end a foot or so off the
ground, then drops it repeatedly, to shake out the unwanted critters. So
what I need to figure out is how to build a mechanism that's driven by an
electric motor that will lift, say, 400lbs a foot in the air, then let go
and do it without falling apart over a loooong winter. Suggestions?

Up your frequency, Steamer.

This calculator does not extend to the range of frequencies that would
be useful, but you could use the formula to discover what range of
acoustical frequencies the little buggers would dislike.

Surround woodpile with acoustic transducers frequency modulated to
mixmaster their innards and the bugs would probably invade elsewhe

http://hyperphysics.phy-astr.gsu.edu...cavity.html#c4

--Winston


Mice and other small rodents are repelled by frequencies in the region
of 25KHz to 35KHz. It needs to be fairly intense (93 dB or better)
and it's best if it is intermittent and frequency-modulated at a low
rate. I used cheap Motorola piezo tweeters, sometimes as little as
$3.95 each.

Tried in two northwoods cabins, worked in both. Man, did they come
outta the woodwork and scurry for the woods when I first turned that
sucker on upon arrival after being away for a while.

Digikey sells transducers in 40 KHz, 92 Khz, 150 KHz and 215 KHz flavors:

http://search.digikey.com/scripts/Dk...rds=transducer

http://media.paisley.ac.uk/~davison/...cct/u_cct.html

--Winston

Those 'ducers aren't good for this. They're either too pricey, too
wimpy or have very limited bandwidth.

Here's what I used:

http://www.electronicpartsforless.co...id=36&df id=1

If ya use a 555 or 556, it needs a simple power amp comprised of a
coupla transistors working from +/- 15 volts.