Our cat, Murray, had gotten into the habit of preferring to drink from a slow trickle in the bathroom sink. This wasn't always convenient for us, so I decided to modify a pet fountain. After checking out several of them, I went with the Drinkwell Platinum. It has a carbon filter, adjustable stream, large reservoir, and is pretty quiet. I didn't see the need to have it run constantly, so I wanted to put a motion detector on it to run only when he came near.
This ws a pretty straight forward project and turned out really well. Murray loves it.
Step 1: Motion Detector
If the fountain is the body of this project, the passive infared motion detector (PIR) is the brain. I didn't have to search very long to find the perfect detector. It was very small and simple to wire into a control board. I found it at http://www.glolab.com . The detector itself fit perfectly into a 3/8 inch hole I drilled in the front of the fountain frame. It took me a little time to figure out the best way to hook it up since it has a dedicated relay out. It turned out that since I was using a solid state relay to activate the pump, the standard out worked best.
The additional items necessary for this project are a small perfboard, 180 ohm resistor, 7805 voltage regulator, AQH2213 solid state relay, 0.1uF capacitor, 10uF 50V capacitor, 1000uF 25V capacitor, a bridge rectifier, 2 Molex KK connectors (male and female for each), and a 3 pin header.
Step 2: Electronic Design
So, the design was very straight forward. The fountain's pump came with a 12 volt AC transformer. The PIR runs on DC. I used a bridge rectifier to convert the AC to DC after the AC has run to the pump. The 12V DC is then converted to 5 volts and regulated through a 7805 regulator. The pump is switched on with an AQH 2213 solid state relay. The schematic shows a 3213, but Digikey was out when I went to order. Th only difference is the mA tollerance, 600mA for 2213, 1.2A for 3213. The 600mA provides almost double the max draw on start up of the pump, so it worked fine. The relay is triggered by the output from the PIR. The LED trigger in the SSR has a max forward voltage of 1.3V at 20MA and the PIR outputs 3.5V. Using Ohm's law:
(3.5-1.3)V / 20mA = 110 ohms, so I used a 180 ohm resistor.
The red and white jumper wires on the breadboard simulate the power to the pump.
Step 3: Power Connection
In order to connect the power to the circuit, I cut off the barrel plug it came with and replaced it with a Molex KK connector.
Step 4: PIR Connection
The PIR mounts in the front of the fountain frame, so it needed 3 wires to connect to the circuit board (+V, Ground, and Output). I termiated these in a simple 3 pin header, bent a little to fit into the tight space. The wires tuck up nicely between the outer fountain frame and the bowl.
Step 5: Circuit Connection
Here you can see the underside of the fountain where the PIR wires come around from the front, and the female KK connector coming from the pump. This space was able to contain the circuit board nicely once I added some one inch standoffs. I drilled from the outside of the fountain frame to screw in the board.
Step 6: Finished!
All that was left was to fill the reservoir and plug it in. Murray took to it right away and the PIR, though continuously re-triggered while he's moving in front of it, shuts off after 30 seconds without motion. The sensitivity is enough for Murray to trigger it when approached, but not when we walk past, about 6 feet away.
Here's a video of it in action, where you can also see where the sensor is mounted.