Motion sensing is the detection of the change in position of an object relative to its surroundings or vice versa. There are many kinds of motion detector methods: infrared, optics, radio frequency, sound, vibration, and magnetism. These methods differ from each other because each of them uses a different medium and detects different subject (e.g. sound: in Doppler effect, motion is detected by the change in reflected frequency).
This project uses PIR (passive infrared) sensor to detect the change in radiation, this can be use on lighting control, temperature control, and motion detection since all objects with temperature above absolute zero emits heat energy in the form of radiation. The term passive refers to the fact that PIR devices do not generate or radiate any energy for detection purposes. It works entirely by detecting the energy given off by other objects.The D204B PIR sensor is used in this project, it contains a material that generates energy when exposed to heat/radiation. The MCP6H94 quad op-amp is used in two stages; amplifier and comparator. The weak signal from the PIR sensor will be amplified by the first two op-amp configured as amplifiers, the amplified signal is then fed to the last two op-amp configured as comparator. The BC548 NPN transistor acting as the switch will be triggered when the comparator’s output gets HIGH, further, switching the transistor will also trigger the relay that is connected to the load (light and/or alarm).