Automatic Twilight Switch

Introduction

Twilight switch

Twilight is exactly the transition period of time from sunset to the beginning of the night. At that time light becomes poorer and poorer from brightness to darkness. As time advances darkness predominates and the natural light source is withdrawing slowly. The visibility of items and things around us is much clearer when the natural light source is present. As it withdraws gradually the visibility of things around us also becomes poorer and poorer. 

To get back the visibility of things around us we should have artificial light sources. The artificial light source maybe lighting a candle or switching on battery-powered illuminating items like electric bulbs etc. In the home surroundings, we can light a small light to improve the visibility of the objects. However, in public places like a big cinema theatre or a big hall or even a pathway or roadways bigger and brighter light source is required. 

In the absence of proper light/ adequate light, any untoward incidence may happen. In the home, we may tumble down on something or fall down not knowing the steps or items on the way. Children may get injured by dashing against some hard objects etc. on the roads poor visibility may lead to accidents like colliding vehicles or human fatal accidents. As such poor lighting condition is dangerous of everything. Hence at twilight to avoid such happenings immediate adequate light source should be switched on. The switching on of other light sources needs manual effort or it may be automatic. Automatic switching on such resources is a welcome feature as it avoids unnecessary hardships.

The automatic twilight circuit schematic

Based on the above deliberations, a versatile automatic twilight circuit design is presented here for assembling and put into practical use in homes and other places that need to combat darkness during the twilight period.

In this circuit, a light sensor is used to detect the intensity of light and switches on the light electronically by the associated transistorized circuit. Just two transistors are used on the switching side and a relay gets activated at its output. The circuit works on a 12V battery supply.  A small lamp is used as a light source to be put on in the darkness. 

Working

During daytime natural light falls on the LDR, so that the relay is kept open and the lamp does not glow. As soon as the natural light, the source light is removed from LDR causes to activates the sensor to trigger the electronic switch and thereby relay gets activated and latched. The switch is now on and the lamp glows. R4 is used to fine-tune the LDR sensor to get activated at the proper light source. 

Parts List

Q1,Q2 = BC549C Transistors

D1= 1N 4001 diode

R1= 4.7K ohm resistor

R2= 33 ohm resistor

R3=3.3K ohm resistor

R4= 2,2K ohm preset

R5= LDR

C1,C2= 10MFD electrolytic capacitor

K1=SPST Relay 9V

PCB design 

A ready-made PCB design is given here for ease of assembling.

Component layout

PCB track

2D view

3D view

To sum up

The assembling of the circuit design is simplified with the readymade PCB design presented here. Pl. give your comments and suggestions for improvement.