This ws a pretty straight forward project and turned out really well. Murray loves it.
Step 1: Motion Detector
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
(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
Step 4: PIR Connection
Step 5: Circuit Connection
Step 6: Finished!
Here's a video of it in action, where you can also see where the sensor is mounted.