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Smart Exhaust Fan Switch

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    First published on: 1-6-2012

    Smart Exhaust Fan Switch


    Exhaust fans in washrooms can be connected to the lighting circuit so that these switch on and switch off with the electric light. But as washrooms are sometimes used only for washing the face or hands, it is not always necessary to switch on the exhaust fan with the light. Advanced techniques such as humidity sensor switching and PIR motion sensor switching can also be used to control exhaust fans but these are not affordable for everyone.

    The simple exhaust fan circuit presented here automatically determines whether there is really a need to start the fan and reacts appropriately. The circuit is powered from an AC mains adaptor that is capable of delivering an output supply of 6V DC.

    Fig.1: Circuit of exhaust fan switch

    The heart of the circuit (Fig.1) is an ordinary reed switch (S1) that is mounted on the cistern. The reed switch is controlled by a small magnet fitted on the toilet lid. When the lid is upright, the reed switch is closed by the magnet. One input of gate N1 of IC1 swings high. The resulting pulse at the output of gate N2 is inverted by gate N3, triggering the timer 555 (IC2). As a result, the relay (RL1) energises, causing the exhaust fan to run for a time period determined by the combination of VR1 and capacitor C3. After this time is over, the exhaust fan automatically switches off.

    Fig.2: 5V DC 1C/O relay

    Fig.3: Proposed Fittings
     Assemble the circuit on a general-purpose PCB and  enclose in a suitable cabinet. Mount the 5V relay    (refer Fig. 2) on the PCB and connect relay  contacts  to the exhaust fan through external wires.

     Fig. 3 shows the proposed fitting of the magnet on   the lid and the reed switch on the cistern.


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    commentPost Comment | 7 Comments

    boopathi R   1200 days ago

    Idea is not very attractive. In my experience a PIR is the ideal situation to run the exhaust when some one in the toilet. This can be fitted at any angle to start detecting the human. Regarding the cost the parts are not costing but the people want to charge the public more because of new technology. I hope at higher volume and change in mindset we can make it cheaper. U can call 9566160513 if U need anythingregards
    commentReply   3 Replies
    Ramesh Gaikwad   1172 days ago

    I want to buy pir motion sensor alarm for home security pl let me know the priceREGARDS Ramesh Gaikwad919822493613917798744844
    sanjeev mahajan   1194 days ago

    yes i am also agree with Mr. Boopathis Views up to some extent. But what is the cost of PIR sensor ........????
    T.K.Hareendran   1193 days ago

    This is a simple idea based on a reed-switch sensor. I agree with you that a PIR sensor can be usedbut it will increase the cost of the circuit. BesidesMost PIR sensors are sensitive to full body movement up to about 40 ft. but are sensitive to hand movement which is more discrete up to about 15 ft and a PIR sensor cannot detect a stationary or very slowly moving body if the sensor was set to the required sensitivity it would be activated by the cooling of a nearby wall in the evening.
    commentReply   1 Reply
    Kousalyaa.G   1189 days ago

    Do u have any idea to overcome the ill effect of PIR sensor
    Kousalyaa.G   1189 days ago

    Ya the idea is quite fascinating...........But as mentioned in the above comments there are some drawbacks......Can someone suggest how to overcome the drawback of PIR sensors.........
    kaleem abadine   1178 days ago

    mind bolwing bro

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