Disclaimer: I'm very new to electronics' projects. This project is thought to be educational for myself. I'm sure my plan is probably too complex or plain wrong. If you have any advise, feel free to comment! It's really appreciated.


The project consists of the following two components:

  • Water fountain
  • Switching board with PIR motion sensor

As soon as one of the PIR motion sensors is triggered, the switching board starts to power the water pump and the fountain is on. After a while, the fountain turns off again.

Water fountain

The water fountain is a commercial one. I used to have a Catit Fresh & Clear. Now I'm using a Cat Mate Pet Fountain. The exact model does not matter though. These pet fountains mostly consist of a plastic container for the water and a water pump therein. You could build it yourself as well in the exact shape you want it to be.

Switching board

The switching board controls the power of the water pump. It either turns it on or off, depending on the signal from the PIR sensors.

PIR motion sensors

I use the PIR motion sensors from Adafruit which are extremely easy to use. They have three connectors: power, ground and signal. The signal is high (3.3V) when the sensor detects a motion. It keeps that signal for a predefined time which can be adjusted with a potentiometer on the sensor. It's hence amazingly easy to power a circuit with it for some time without using a microprocessor or timer.

Switching Board

The PIR motion sensor and the relay are powered using an additional power source (4.5 VDC). The water pump is powered by its power adapter on a wall outlet (12 VAC).

The switching board turns the water pump on and off (by closing its circuit). If a motion is detected by the PIR motion sensor, the following happens:

  1. The PIR motion sensor sends a high signal (3.3V) on the yellow wire
  2. The transistor routes the battery power from its collector to the emitter, thus closing the circuit of the relay's coil
  3. As the relay's coil is powered, it switches and thus closing the circuit of the water pump.


  • One PIR motion sensor is not enough to detect motion all around the fountain. The goal is to have multiple sensors which are OR-ed together.