[KYHAM] Doghouse 12 volt fan

[wa4qal@ix.netcom.com]

That would be my first approach, too.  Sometimes, simpler is better.

However, after thinking about it for a few minutes, I realized that
version 2 might add some more complexity.  If you're really going to
use solar cells to charge a battery, then it might be worth considering
a battery charge monitor to prevent the batteries from being=20
overcharged, or from running them flat (Most batteries don't like being
totally discharged.).  This could be accomplished with a low power=20
microcontroller that measures the state of the battery charge, and
determines whether to feed power from the solar cells into the=20
batteries or not.  It would also sense the state of the battery charge,
and determine whether there is enough energy in the batteries to
run the fan, or whether the fan should be shutdown (even if the=20
temperature is above the threshold) to preserve the batteries if
they have a low charge. =20

Additionally, the microcontroller could even determine the speed=20
at which the fan operates at in order to minimize the energy
usage from the batteries.  Plus, it could determine the outside and
inside temperature, and determine if it made sense to run the fan
(e.g., If the outside was 90 degrees, and the inside was 90 degrees,
then even though the inside was above the threshold of 85 degrees,
it wouldn't make sense to run the fan.).  Also, as an added benefit,
it could slowly start and stop the fan to avoid frightening the dog
(Suddenly switching a blower from off to full on can make a rather
frightening noise.  And, a high tech dog house won't be of much good
if the dog refuses to use it.).  The speed control could be performed
by pulse width modulating the power to the fan motor.

If you really want to get involved with creeping featuritis, you could
have the microcontroller even record the inside and outside=20
temperatures periodically and allow them to be uplinked to another
computer, either via a hardwired link, an infrared link, or a RF link,
thus providing long term weather/temperature information.

Of course, none of this will be easy to develop.  There are quite a=20
few low power, rugged microcontrollers available (I'm a fan of the
Microchip PIC series, although Atmel makes some also, as well as
other companies.).  You'll probably want one with a couple of analog
to digital channels on it to simplify the interfacing for the temperature=
=20
sensors (e.g., Thermistors?  Semiconductor temperature sensors?)=20
and voltage monitors.  However, developing the program for such a=20
controller may require many weeks or months of effort. =20

I suppose that, in some ways, the level of complexity could approach
that of a satellite spacecraft controller.

Or, you could go with the bimetallic switch.

Dave
WA4QAL

-----Original Message-----
From: Tyler Allison <tyler@allisonhouse.com>
Sent: Apr 6, 2004 9:41 AM
To: Kyham <kyham@mailman.qth.net>
Subject: Re: [KYHAM] Doghouse 12 volt fan

> Hi Tyler,
>
> If your project were for the space program, a simple dished disk made of
> bimetal =EF=BF=BD a simple snap on and off thermostat would probably be u=
sed
> because
> it consumes no power and can handle about 5 amps would be used.  Using a
> 5-amp switch to control 15 amps almost brought Apollo 13 to an end.

Thanks everyone who responded on list and off. Everyone said the same
thing. Building a circuit was over engineering ;) which proves once again
that I think too much. ;)

Lots of great ideas!  Thanks.

Anyone interested in the project might find this entertaining:
http://www.allisonhouse.com/project/doghouse/

-Tyler