The submit describes a basic automatic PIR managed fan circuit for school college use, which replies and switches ON merely in the existence of a human (students) in the classroom.
The Design
The model would require some form of human IR sensor to be incorporated, for instance a PIR sensor device which appears to be the most effective and useful for the suggested use.
Including a PIR sensor tends to make the design fairly easy considering that many of the complicated circuitry is taken care of within the unit itself. The sensor simply ought to be built-in with a activating phase and a properly rated power supply as presented in the following diagram.
In the presented diagram you can easily observe a regular preprogrammed PIR module, a 7805 voltage regulator IC stage for providing the PIR, and a effortless 12 V transistor/relay driver stage.
The PIR module has three terminals, the best one is the ground terminal, center one is the positive +3.3V or +5V, and the left terminal is the responsive output lead of the device.
When the specific designated (+) and (-) terminals of the PIR device are linked to the stipulated supply voltages, the device immediately turns into responsive and commences "thinking".
No human occurrence or movement ought to be produced ahead of the unit's lens through this initial turn on period for around a minute or so, until the device locks ON and puts itself into an alert or a ready stand by position.
The unit now evolves into ready and reacts to even the slightest human movement or existence in front of its lens by producing a positive supply at its output terminal, this high at its output terminal continues as far as a human occurrence is identified within a radial selection of around 20 meters in front of the PIR device.
The output becomes a zero voltage the moment the human existence moves away or is taken away.
The above precise high/low voltage reply at the output lead turns into ideally suited or available for a transistor relay driver level as revealed in the diagram.
When the PIR output is high as a result of the occurrence of a human (children in classroom), the transistor BC547 base obtains the +3.3V out from the appropriate lead of the device and immediately switches ON the relay.
The relay consequently switches ON the fan and the system remains ON provided that the students occupy the premise.
When the students entrust and vacate the idea, the PIR instantly switches OFF its output to a zero voltage level, in spite of this the existence of the 470uF/25V capacitor at the output lead of the PIR stops the BC547 from obtaining switched off instantaneously somewhat maintains it ON for a couple seconds more after the PIR has reverted its output to zero.
After this delay the BC547 also gets deactivated, switching OFF the relay and the fan or almost every other preferred load in any way that could be wired with the relay.
The above circuit might be efficiently altered as provided below for working lights, with a feature making certain that it's executed only at nighttime and not throughout the daytime when sufficient daylight is available.
