Motion detectors are small electronic eyes that detect infrared waves — heat waves emitted from moving objects. If these waves cross the sensor’s sensitivity zone, the device electronically switches on the lights.
A sensor consists of two sections: the transmitter section and the receiver section. The transmitter section uses a 555 timer and IR sensors, while the receiver section uses a photo transistor, another 555 timer, and an alarm.
The transmitter section sends the beam to the receiver through a voltage divider circuit. The frequency of the beam depends on the RC constant of the 555 timer. The timer also triggers the alarm by releasing a positive pulse when the sensor’s beam breaks through the divider circuit.
In the receiver section, the beam travels through the IC, which conducts through the photo transistor and causes the alarm to be triggered for a specific time that also depends on the RC constant. The IC also conducts to pin 14 of the BC557, which activates the red LED and shuts off the green LED.
To build a simple motion detector, you’ll need a 555 timer, an infrared sensor, and an LED. The 555 timer is used for timing the detection and triggering of the sensor, and the infrared sensor is used for generating the beam that the IC sends to the photo transistor.
This circuit is easy to assemble, but be careful not to misplace any components. Using the right parts is essential, and you should also read the manual that came with the sensor before installing it.
The best place to install a motion sensor is opposite a main entryway, so it can catch intruders as soon as they walk through. You can also use them in bedrooms and other spaces that aren’t usually open to guests.
Ideally, your motion sensor should be 6 to 10 feet above the floor and placed so that most of movement occurs across its sensitivity zone. But you can also mount it further away from the light itself if that’s the best option for your space.
When you’re mounting your sensor, make sure it’s not near any hard surfaces that would block the infrared waves, like drywall anchors or studs. This can make it harder to trigger the sensor, and you may need to disassemble your device in order to remove it during maintenance.
You can also install a motion sensor in the ceiling, if you prefer. But you’ll need to make sure that the wires don’t touch any studs, since these can cause the sensors to fail and cause an electrical hazard.
How to connect a motion detector diagram
The most important step in connecting a motion detector is putting the power wires and the load wire on the correct connectors. You can do this by marking the hot wire and the load wire with electrical tape before you install it. Then, you can use a non-contact voltage tester to check that the wires are properly connected and have power.