Subject: Re: electronic cat doors

From: [email-masked] (Steve Mason)
Date: Thu, 01 Aug 1996 17:00:57 GMT

On 29 Jul 1996 23:23:55 GMT, [email-masked] (Allan Creighton) wrote:

>Sorry if this is " one " of those topics
>
>Does anyone know of any commercial units, sites etc or has anyone
>bothered to make their own. I need to discriminate between my cat
>and the rest of the moggies.
cc by email

Here's a  humorous post about building your own, from one of the
sci.electronics groups.
 Reposted without permission.

From: [email-masked] (Grant Fair)
Message-ID: <[email-masked]>
References: <[email-masked]>
Date: Wed,  6 Sep 95 01:00:00 -0500
Organization: CRS Online  (Toronto, Ontario)
Lines: 37

I built two cat doors, and lived to tell about it...

The first had a footswitch inside and out (2 flexible pc boards
separated by spacers at 4 corners. Cat steps on it, joins the 2
pcb's...).

When a footswitch closed, this turned on a low voltage DC relay, which
turned on a 110 volt washing machine relay (used), which pulled the cat
door open.

When the footswitches were both open, the relays turned off and the
hinged door returned to vertical, where a magnetic latch pulled it snug.

First time I tried it - WITH a cat - when the relay fired - WHACK! BOING
BOING - the cat screeched, jumped and took off.

Back to the drawing board.

Same foot switches. No relays. An op amp circuit drove a small DC motor,
which ran a pulley, which slowly, smoothly, and oh so quietly wound up a
string on a drum, which opened the door. When it reached it's upper
limit, a mercury tilt switch told it to reverse. As long as a foot
switch was closed, it quietly "hunted" back and forth about 1/4" until
the cat (I thought) would get off the footswitches. The door would
return to  vertical, the magnetic latch latched, and  the motor turned
off.

It was beautiful. It worked like a charm, so smooth, precise, quiet and
reliable. Until I put a cat on it.

As I mused over the new quiet smooth design, the cat's reptilian brain
heard WHACK BOING BOING. From a time before. The cat screeched and ran,
and would not go near it. Ever..

Now, you could add a Hall effect device and a magnet round the cat's
neck, and try design two...but my money's on getting one from the store.
That's what I did...