Useful Electronics: Cat Accident Preventer February 23, 2009

I am the owner of a generally very awesome product – a Litter Robot automated cat litter box.

However, we occasionally have an issue where the box malfunctions in some way. This is either because

  • The switch which gets tripped when the cats go in stops working, thus never initiating the self-cleaning service. Horrible consequence: the house starts to smell because the crap stays in the sand.
  • The box ends up stuck in the ‘dumping out the crap’ state (upside down.) Horribler Consequence: the cats refuse to use the box, thus finding alternative (and far less pleasant) places to relieve themselves.

If you are familiar at all with the delicate scents of cat defecates you will appreciate my desire to eliminate both of these issues.

So, I thought to myself that if I only had some way to track when the box was in it’s normal state, and not in it’s normal state, I would be able to alert my wife and I to either malfunction state soon enough that we could deal with it.

Hence, the below design was born.

Litter Robot Malfunction Detector

It uses a very nice and yet simple sensor (with a pullup resistor to get a clean signal) called a Reed Switch which creates a closed circuit when it’s near a magnetic field. I can epoxy this to the un-moving base of the Litter Robot, and epoxy a small magnet to the corresponding spot on the inside of the dome. (Inside rather than outside so it does not interfere with the dome’s rotation.)

I then read this sensor from an Arduino board. This would be ridiculous overkill just to get a simple binary signal into a computer, but I’ll be using the Arduino for other home automation tasks. (Temperature Sensing, power switch control, etc.) Whenever it changes state, it can send a message over the Serial-over-USB cable to my very low power home NAS. (Which will probably be another blog entry, as it’s a work in progress.) This can store in a local database every time the state changes, and have a simple Perl script wake up every 20 minutes to see

  • If the box has not rotated for more than 6 hours
  • If the box has been off the ‘home’ position for more than 40 minutes.

It then sends us an SMS (just an email to 10 digit to alert us. This is a nice form of alert because if I’m home, it might wake me, but not anyone else. If I’m at work, I’m close enough to make a quick lunch break trip home and resolve it before anything stinky happens. If I’m on a trip, I can give a friend with house keys a quick call and ask for a favor.

I have ordered all the parts for this project and should be ready to go soon. Other than the Arduino, the whole thing can be built for about $2 in parts. I’ll hopefully be posting an entry soon with the Arduino and Perl code that makes it all work and photos. (That is, unless I fail in an epic fashion.)