Simple PIR Motion Trigger

Low Part Count Motion Trigger

Their are several ways you could make this same device for many different uses. Other options for what gets triggered and how it reacts could be accomplished by adding in a micro controller to better control timing or have a more elaborate routine run.

This is a very simple way to use motion to active a prop, or switch a light. The final design I used has 2 relay outputs, one of which is connected to 2 plugs and 110 volts and the other has 3 wires that act as a dry contact switch, one set opens as the other set closes.  This could be used to trigger a separate show controller, prop, audio player or video player.

Parts Used:
Plastic Enclosure
PIR Motion sensor
dual relay module
110 volt to 5 volt power supply
2 extension cords
2 pair phone wire
Crimp connectors and glue

Enclosure: I chose a case that I had on my shelf it was large enough to fit everything inside and was non-conductive. Any case will work as long as it is large enough to fit all the parts inside. I would recommend non metallic to minimize the risk of shorting out any of the components inside.

The only modification that are needed for the case is to drill a hole large enough to fit the dome on the sensor though, and to drill holes to allow the cables to exit out of the case. I drilled 4 holes in the bottom to allow power in, 2 power cords out and the 4 conductor cable out.

Motion sensor and relay: To keep this trigger as simple as possible I decided not to include a micro controller in the design and went with just 2 main parts, the PIR sensor and a dual relay module. This keeps the part count low and makes the wiring simple. The motion sensor has 3 wires +5 volts, output and ground. The relay board has 4 wires +5 volts, 2 input wires and a ground, This particular relay board is activated by pulling the input pins low, while the motion sensor I used goes high when it is triggered and is low when in a waiting state. This means my relays are active when the trigger is not triggered and deactivate when its triggered. This is not a problem since the relays have both the NO and NC pins.

Their are only a few connections to be made you will want to take both pins for 5 volts and tie them together and do the same for the 2 ground pins. The other connection you will make is to take the output pin of the motion sensor and connect it to both of the input pins for the relay board. The power for this will be explained in the next step.

High voltage wiring and power supply: If you have never worked with line voltage before be sure to get someone who has to help you.


Main power: To keep my wiring simple the 110 volt plug for this box will provide the power to the plugs that get switched by the relay and to the small power supply that will give 5 volts to the sensor and relays. To start I crimped on 2 short wires rated for 110 volts to the end of the power cord I used. This makes wiring everything  just a little easier as it give me one side for constant power and one for the switched power. Both the plug and outlets that I used for this project were 12 foot 2 wire extension cords. I simple cut off the plug and was able to use both. I decided to take advantage of the fact that the relay had connectors for both open and closed contacts and wired this so that it would power one outlet or the other, and when activated would switch. To wire this side I took all my neutral wires and crimped them together. The hot wire from the plug will go to the central pin on the relay while the hot wire from each outlet is connected to the NO and NC sides of the relay terminal. Use caution and common sense with this since high voltage can be very dangerous. Once everything is crimped I made sure there were no shorts, loose wires, or exposed wires and moved on to installing the power supply. 

Power Supply: I got a small 5 volt power supply to use for this project, they can be ordered online for a few dollars you could also choose to use an external power adapted if you have one around. This will only power the sensor and relay boards, The board has 2 sides one for high voltage in and one for low voltage out. I crimped the input side to the remaining 2 wires from the last step on my plug. Make sure to check with a multi-meter to make sure your voltage and polarity are correct. The +5 volt wire will get connected to the set of wires for the positive from the relay and sensor, while the negative will get connected to their negative connection. Once this is done the unit should power up and be ready for testing.

Dry contacts: To make this trigger as useful as possible I used the second relay on the board to act as an external trigger. I used a 4 conductor wire, using the red and black wire as a common and the green and white for the NO and NC connection. This can be used for just about anything, You can use it as a simple dry contact closure for animated props or triggering a micro controller to do more elaborate routines. You could also use to trigger a video player or audio player to add to your scene.

I did a power on test to make sure everything was connected correctly and then closed up the case using 4 screws and making sure not to pinch any wires with the lid.

Testing:
I did a few quick tests to make sure that this box would work as expected, The timer and sensitivity can both be adjusted to meet your needs.