The electronic DIY kit shown is an automatic lighting for the bathroom, simple and cheap. The light turns on automatically when the bathroom door is open and stays on when it is open again, the lamp / LED going out after a short delay.
This automatic circuit saves energy and helps visitors a lot, especially at night.
Electronic scheme of automatic bathroom light switch
How does the electronic scheme work?
The heart of this circuit is the meter CD4017 CMOS with decoded output. With each pulse received at the input, this integrated circuit leads to the next output. Output "0" (pin 3 - IC1) controls a 1W light source (LED 2) through a driver transistor (T1). Initially, when the circuit is powered, IC1 is reset by the RC network and, as a result, LED1 lights up.
When the door is opened for the first time, switch S1 is opened and, as a result, IC1 is "touched" by the clock pulse generator. Now LED 1 (green) it goes out too LED2 (white) it lights up. IC1 remains in this condition to provide interior lighting even if the door is closed.
However, when the bathroom door is opened again, IC1 is "touched" again and this resets the chip again through the signal from output 2 (pin4) from IC1 to D1 (1N4148).
LED responses to S1 switch states
| Door / Status | S1 Switch | LED 1 | LED2 |
| Closed / Toilet free | Closed | On | off |
| Opened / In | opened | off | On |
| Closed / Occupied | Closed | off | On |
| Opened / Out | opened | On | off |
List of required components:
IC1 = CD4017;
T1 = 2N2222 (or BC547);
D1 = 1N4148;
LED1 = 5mm Green;
LED2 = 3.6V / 1W White;
R1 = 10K / 1W;
R2 = 100K / 1W;
R3 = 2.2 Ohm / 1W;
R4 = 1K / 1W;
C1, C2 = 10 uF / 16V;
C3 = 100nF;
S1 = N / O Push Switch;
J1 = DC Socket (for 5V power supply).
Bibliography:
https://www.electroschematics.com/
It's a good exercise for a beginner in electronics. It should not be used by those who are knowledgeable or ready to buy.