automatic bathroom fan controller circuit

Automatic Bathroom Fan Controller

This automatic bathroom fan controller circuit design is a lamp and fan motor control with a delayed switch off. This automatic fan control is commonly used in toilet and bathrooms. When switch S1 is closed, the fan motor and the lamp turns on. When switch S1 is opened (switched off), the lamp goes out but the fan motor will keep running for another 3, 6 or 12 minutes linger (set by S2). This delayed switching off of the fan ensures that the unwanted odor is really fanned out the toilet.

Schematic of the automatic bathroom fan controller circuit

automatic bathroom fan controller circuit

The heart of the bathroom exhaust fan circuit is the SAB0529 IC. It is a programmable extended time timer brought to the market by Siemens. This IC can be programmed to time from 1 second up to 31.5 hours. This extended time capacity is achieved by the IC by using the power line frequency as its time base.

The bathroom fan light control circuit is commonly used to control inductive loads such as the case of fan motor. For this reason, a current synchronization is necessary. This is done with resistor R6. In addition, a capacitor C2 is connected between pins 15 and 1. This capacitor sets the pulse length at the output pin 16. If one decides to use a different triac, one needs to change the value of R5 .

This resistor sets the level of the trigger current, in this case 5 mA. The syc resistor R6 must be changed also. If the triac power and holding current (Ih) are known, one can get the value of R6 from the table below:

R6 value


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  • Jayant

    I am interested in 6 pcs. of automatic bathroom switches for exhaust fan as mentioned sbove. Kindly suggest where will I get those of best quality. Also suggest the best quality with minimum noise exhaust fan for toilet / bathroom and kitchen.

    Any other modern electronic gadgets please mail me.


  • Miguel

    What changes should i do to use it with 120 VAC?

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