This system consists of two distinct components: a cat-sensing pressure mat and a circuit to power the lights and fans. I'll show you how to build both.
Note: The mat can be used as a simple switch to activate any circuit. Likewise, the circuit can be activated by other means. Today's your lucky day - this is like 3 Instructables in one!
Wire and connectors (male | female)
Breadboard or protoboard or PCB
1x 12v AC/DC Adapter
2x 12v PC fans
1x 12v relay
1x 555 Timer IC
1x 10nF Capacitor
1x 0.47μF Capacitor
1x 470μF Capacitor***
1x 10kΩ Resistor
1x 350kΩ Resistor***
Of course, the most important ingredient is love.
*I originally selected posterboard because of it's small profile. Unfortunately, the top layer turned out to be a little too flimsy/unreliable/inconsistent, so it was replaced with foamboard.
**For the lighting, I used 12 LED's from a reel I purchased online. I bought these specifically because they only required a 12v power supply, which matched the PC fans I was using. You may find something more suitable for your needs.
***The values of these components affects the timing of the circuit. For more information, see step 7.
Step 1: Cat Mat: Functional overview
Basically, two pieces of aluminum foil are physically separated by foam. When weight is applied, the foil layers come together to make contact. When weight is removed, the foam lifts and separates the two foil layers.