When the button is pressed the Arduino board will put pin 2 in HIGH state, meaning 5V on pin 2. This voltage is used to drive the transistor that will switch ON the relay and the load (in our case the ...

To solve the problem without sourcing a new switch, [Jean-Noel] built his own Arduino based Dahlander switch. This consists of three relays that select the wiring configuration for each speed mode.

The ‘unhackable’ switch, which resembles a MIDI sequencer input, runs on an Arduino Nano Every and uses a relay to directly control the power state. Instead of having one keep-alive button ...

After wiring up each outlet so it can be controlled independently, he set out designing a four port relay board. This was a pretty simple build – four 10 Amp relays and a few terminal blocks.

Or just use a MOSFET if the relay isn't very fussy. Or, use a combination of the Arduino driving something like the above timer relay, which itself will pull the 12V relay high if that's all it needs.

If the stench from your cat's litter box is a bit too much for you to take, consider rigging together an exhaust system using a 120mm computer case fan, a 12vdc power supply, 4" flexible dryer ...