Design of automatic controller for bathroom lighting and ventilation fan

In order to remove the odor in the bathroom in time, many families have installed ventilation fans, but some guests or children often forget to turn on the ventilation fans. In order to solve this problem, an electronic device that can automatically control the ventilation fan and lighting is designed, which does not add any trouble to people who go to the bathroom, and can automatically ventilate and turn on and off the lights, which is energy-saving and convenient.
Working principle The working principle of the device circuit is shown in Figure 1 (click to download the schematic diagram). It consists of a magnetic switch circuit, a monostable delay circuit, a lighting control circuit, a ventilation fan control circuit and a power supply circuit. When the bathroom door is closed, the permanent magnet ZT is very close to the normally closed reed switch AG. Due to the magnetic force of ZT, the contact piece C in AG is disconnected, and the transistor VT is cut off without bias current. At this time, the ② pin of the time base integrated circuit IC1 is high, so IC1 is in a reset state, and the ③ pin of IC1 outputs a low level, and the relay J has no current and is not attracted, and the ventilation fan and lighting are both in a power-off state. Once someone enters the bathroom, the distance between ZT and AG will increase at the moment of entering the door, so that the magnetic lines of ZT cannot act on AG, so the two contacts in AG are reset and contacted, and the transistor is biased and turned on. After VT is turned on, the ② pin of IC1 becomes low level (only the saturation voltage drop value of VT), and IC is triggered and set. At this time, the ③ pin of IC1 jumps from the original low level to high level, and the relay J is excited and attracted. After J is attracted, its normally open contact J1-1 is closed, and the ventilation fan M is powered on and starts to exhaust. At the same time, another group of normally open contacts J1-2 of J is also closed, and the lighting lamp H is powered on and lit, and its height can be adjusted by RP. If it is daytime, due to the strong light shining on the photoresistor CdS, the internal resistance of CdS is very small, and the voltage across the phase-shifting capacitor C6 is not enough to turn on the trigger diode 2ST, so VS has no trigger current and is blocked, and the lighting lamp H will not light up. At night, since there is no sunlight shining on CdS, the internal resistance of CdS becomes very large, which is equivalent to an open circuit. At this time, 2ST is turned on, VS is turned on, and the lighting lamp H is lit. After opening the door and entering the bathroom, although the door is closed again, at this time, due to the monostable effect of IC1, the circuit is still in the ventilation and lighting (night) state. When opening the door and leaving, ZT moves away from AG, and then closing the door again, causing ZT to approach AG again. After a delay, the light and ventilation fan will automatically stop working. In order to ensure that the door is usually closed, it is necessary to place a tension spring outside the door or replace it with a loose-leaf with a torsion spring, so that the door automatically closes after leaving, ensuring that ZT and AG are close. The device is stepped down and limited by capacitor C5, and the full-bridge U is rectified by C4, and VDW is stabilized to supply DC power to the circuit. Component selection and production See the table below for the component list.

serial number	name	model	quantity	serial number	name	model	quantity
R1, 6	resistance	10K	2	C5	Metallized capacitors	0.068u Withstand voltage ≥400V	1
R2	resistance	5.1K	1	C6	Metallized capacitors	0.1u/160V	1
R3*	resistance	1M	1	VD	Rectifier diode	IN4001	1
R4*	resistance	51Ω	1	VDW	Zener diode	12V	1
R5	resistance	1M/1W	1	2ST	Bidirectional trigger diode	Breakover voltage 30-40V	1
RP	Potentiometer	100K Linear	1	VT	Transistor	9014	1
CdS	Photoresistor	MG45-32 and other non-sealed types	1	VS	Bidirectional thyristor	3A/400V	1
C1, 3	Polyester capacitor	0.01u	2	IC	Time Base Integrated Circuit	NE555	1
C2	Electrolytic Capacitors	47u	1	J	Electromagnetic relay	JRX-13F	1
C4	Electrolytic Capacitors	100uF/50V	1	AG	Reed Switch	Φ4mm Normally Closed	1

The monostable working time of IC is determined by the value of 1.1R3C2. The brightness of the lighting lamp H can be changed by adjusting RP. RP can be a potentiometer or a solid core variable resistor. When it is found that the relay J is weak to attract, the resistance value of R4 can be reduced or simply omitted. After the entire circuit is welded and debugged, it can be put into use after being placed in a plastic box.