Do the local animals think your front lawn is their personal toilet? Do ninja assassins keep trying to sneak into your house? Keep these unwanted visitors away with a motion activated sprinkler system. As soon as they step into your lawn, a passive infrared motion sensor detects the intruder and turns on the sprinkler to chase them away.

Project Steps

Assemble the Motion Activated AC Outlet

To control the sprinkler, we need a motion-activated AC outlet. These can be purchased from some hardware stores or online. I made one from an old motion-activated security light.

Start by disconnecting the motion sensor unit and removing it from the original housing. Now you need to identify each of the connecting wires; in this case, the green wire was ground, the white wire was neutral, the black wire was the hot input to the sensor, and the red wire was the hot output from the sensor. This color code may vary depending on where you live.

Now you need to connect the wires from the motion sensor to the appropriate wires on the power cord(s). Start by cutting the power cords and separating each of their internal wires, then strip the insulation off the ends of each of the wires. When connecting the wires, all the connections should be made with insulated twist-on wire connectors. Start by connecting all of the green wires and any bare wires together. Next, connect one wire from the male power cord and one wire from the female power cord to the white wire on the motion sensor. Then connect the third wire from the male power cord to the black wire on the motion sensor. Lastly, connect the third wire from the female power cord to the red wire from the motion sensor.

As a safety precaution, I enclosed all the connections in an insulated plastic housing. Now you have an AC outlet that can be activated by a motion sensor. To use it, just plug the male power cord into a wall outlet and plug your appliance into the female power cord. The motion sensor should be able to power appliances that are rated as high as the original lights. In my case, the original lights where three 100 watt halogen lights, so it should be capable of driving circuits up to 300 watts.

Find an AC Adapter That Can Activate Your Sprinkler Valve

Most sprinkler valves are activated by a 24VAC signal from their controller. For this project, I used an AC power adapter to turn it on and off. It doesn’t need to output 24 volts in order to work — I was able to activate the sprinkler valve with adapters that list their outputs as low as 9 volts. This is because unregulated power supplies will output different voltages depending on what circuit you are trying to power. It is possible to calculate this, but for the purposes of this project we can just use some quick trial and error. The easiest way to see if an adapter will work is to just connect it to the terminals of the sprinkler. If you hear a click, the sprinkler valve was activated.

You should also test it with the adapter plugged into the motion activated AC outlet that you just built. The output voltage of some motion sensors will be slightly less than the voltage of a regular outlet, so you want to make sure that the adapter can still activate the sprinkler valve when it is plugged into the motion activated outlet.

Connect the AC Power Adapter to the Sprinkler Valve

Next you need to connect the sprinkler valve to the power adapter. First, I cut the DC connector off of the cord on the power adapter. Then I separated the two wires and stripped the insulation off of the ends. You can now connect these wires to the wires on the sprinkler valve. I just soldered the wires together. Because this device will be working around water, I highly recommend insulating the connections with either liquid electrical tape or heat shrink tubing. If you use heat shrink tubing, be sure to insert the tubing onto the wires before soldering them together.

Choose a Good Location For Your Motion Activated Sprinkler System

You need to find a good place to set up your motion activated sprinkler. First decide on the target area that you want the sprinkler to be able to hit. Then position the sprinkler so that it will cover this area with the spray directed out so that it will chase the intruder out of your yard.

Then decide on the best location for the motion sensor. You want it to be well hidden but still have a clear view of the target area. You also want to avoid anything that will cause the sensor to be trigger accidentally such as leaves that wave in front of the sensor. I chose a nice shady spot under a tree.

Connect All the Parts

First, you need to attach the two adapter fittings to the sprinkler valve. The fitting with a female garden hose connector should be attached to the “IN” port. The fitting with a male garden hose connector should be attached to the “OUT” port.

Next you need to connect the sprinkler valve to the faucet, the sprinkler, and the hose(s). I connected one hose between the faucet and the sprinkler valve. Then I connected a second hose between the sprinkler valve and the sprinkler. Using two hoses gave me a little more freedom in where I could position the motion sensor and the sprinkler, but you could also connect the sprinkler valve directly to either the faucet or the sprinkler. Once all these connections are made, turn on the faucet all the way. There may be several seconds of flow through the sprinkler while pressure builds up in the hose.

With the water handling parts in place, you can now connect the electrical parts. Plug the motion activated AC outlet into the outlet on the wall of your house, then plug the sprinkler valve’s AC power adapter into the motion activated outlet. You can also use an extension cord to give you more range. Now whenever the motion sensor detects movement, it will turn on the sprinkler.

Trouble Shooting

This system works best at night because the sensor doesn’t get any interference from the sun. If you want to use it during the day, you may have to spend some time troubleshooting it.

Many motion sensors (especially the ones that are designed for security lights) are designed to shut off during the day. They have a light sensor that deactivates the system when it is bright outside. You can get around this by covering up the light sensor with a piece of duct tape.

The heat from the sun can trigger the motion sensor in several ways. If the sun suddenly goes behind a cloud it can change the temperature of some places in the field of view and trigger the sensor. Changing light from moving leaves can also trigger the sensor. It can help to position the sensor in full shade and away from large leaves.

Most motion sensors have a wide field of view and any motion around them can activate it. You can reduce its sensitivity and narrow its field of view by putting small pieces of tape over part of the sensor.

Watch as Your Motion Activated Sprinkler Chases Away Unwanted Visitors

Whenever a person or animal wanders into your yard, the sprinklers will turn on and chase them away. It is just one more tool to add to your home security system — or you can just use it to prank your friends.

A more benevolent person could use a similar system to turn off sprinklers as people walk by. You could do this by adding a relay or a TRIAC to invert the output so that the sprinkler will turn off when it senses motion. But that is a different project.