Yard-light motion sensors are a cheap and easy way to add some automation to your haunt. Just hook up power to the sensor, hook the output to an outlet, and you can control anything that runs on 120VAC. But what if you want to control something else? It turns out it’s pretty easy to modify these motion sensors so the output just acts like a normal switch or button. Here are some of the things you can control with a modded motion sensor:
- LED spotlights
- Any Halloween prop with a “Try Me” button
- CD / MP3 player
- Fog machine
- Air canon
- PowerPoint presentation
Basically if you can control it with a switch or a button, you can control it with a motion sensor.
What you need
- Yard-light motion sensor
- Soldering stuff
- Utility/Xacto knife
- Insulated wire
You don’t have to get fancy with the motion sensor. Good = $8 El-Cheapo unit from hardware store. Better = $0.25 unit you got from a garage sale (that’s how much I paid for the one in this example).
Take the motion sensor apart
First separate the sensor unit from whatever base / sockets it is hooked to. As you do so make a note of how everything is hooked up. You need to identify which color wire is what. Here is the scheme used by most sensors:
- White = Power In (Neutral)
- Black = Power In (Hot)
- Red = Switched Power Out
Also take note of which incoming power wire is connected directly to the flood lights. It will most likely be the white (neutral) one since the sensor switches the black (hot) one. I have seen sensors that switched neutral before though.
Now take apart the motion sensor itself and pull the board & wires out. How you do this will depend on the exact sensor you have.
Find the relay
Look at the component side of the circuit board. You need to find the relay (the part that acts like the switch). It’s usually a blue plastic box looking thing. It may be black or clear or some other color, but most of the ones I’ve cracked open had blue ones. Here is the relay in my sensor:
Identify relay connections
Here is a simplified schematic of how the relay will be connected:
You’ll need to identify the following connections on your relay:
- Power in
- Switched power out
- Coil in (x2)
It shouldn’t be too hard. Here are some hints:
- The power in connection should go to one of the power in wires (most likely black, but maybe white)
- The switched power out connection will go to the red output wire
- The remaining connections are for the coil and probably go to a bunch of random circuitry. You don’t really need to worry about these.
Here are the connections on my sensor:
Cut the power
The first mod we need to do is to cut the power going through the relay without disrupting power to the rest of the circuitry. If the relay connection is at the opposite end of a trace from the power coming in then it’s simply a matter of cutting the trace right before the relay connection.
When you cut the trace, make two cuts then use the knife to peel up the copper in between. If you just make a single cut you run the risk of electricity arcing across the small gap.
The other possible scenario is that the relay will be in the middle of the trace, with power coming in one side and some circuitry connected on the other. In this case you’ll need to cut the trace on either side of the relay connection, then solder a jumper wire that bypasses the relay.
Add a second output wire
Now that there is no power going through the relay, we need to solder on an additional wire to the relay connection we just isolated.
That’s it for the modifications. Put everything back together.
You should now have a motion sensor with four wires coming out of it. The black and the white wires provide power to the sensor and should be connected to 120VAC. The red wire and the new one you added (purple on mine) are connected to the contacts on the relay. When the sensor detects motion, they are connected together. When it times out or sees no motion, they aren’t.
It’s very important that you test your newly modded motion sensor with a meter before you go connecting it to any of your equipment (just in case you didn’t successfully remove power from the relay).
Activate “Test” mode on your sensor if it has it (it will work even if it’s light in the room and only stay on for a very short period of time when it is triggered).
Hook the black and white wires up to power.
Set your meter for AC volts.
Trigger the motion sensor by waving your hand in front of it.
Check for voltage between the red wire and the white wire. There shouldn’t be any.
Check for voltage between the red wire and the black wire. There still shouldn’t be any.
Check for voltage between the red wire and your new wire. Should still be ~0V.
Now set your meter to test for continuity (keep it connected to the red and new wire). You should get continuity (~0 ohms) when the sensor has been triggered, and none (display probably reads “1”) when it hasn’t been triggered.
If your sensor passes all the above test then you are ready to start controlling props with it.
Connecting the sensor
This is the part where your imagination comes in. As I said before, you can connect the two output wires to anything that is normally connected to a switch.
- LED spotlights: Connect the power supply, sensor and LED in series. Replaces normal on/off switch.
- Prop with “Try Me” button: Clip the two wires that go to the button and connect them to the sensor’s output wires.
- CD/MP3 player: Solder two wires to the play button. Connect the wires to the sensor’s output wires. This does not affect the functionality of the player’s own play button.
- Fog machine: Connect two wires between the fog button and the sensor’s output wires.
- Air cannon: Hook the sensor’s output wires up in place of (or in parallel with) the cannon’s fire button.
- PowerPoint presentation: Hack a keyboard so that the sensor’s output wires connect across whatever two contacts the space bar connects to.