Automatic night light circuit using SCR

This automatic night light circuit controls the turn the power off consumption in home automation. If it is daytime working to break the circuit.

But at night is connected to a working electrical AC 220 volts. Such as the opening and closing of the bulb.

This lamp will illuminate when the light bulb goes off into the evening and on beginning to dawn.

Automatic night light circuit using SCR

Automatic night light circuit using SCR
Here is Automatic night light circuit using SCR and LDR without Relay!

How automatic sunlight sensor circuit works

The circuits ready working. When the male plug, or for the circuit to the AC line power at 220 volts. The plug socket is connected to appliances in the home. Or connect with bulbs.

The circuit is based on the brightness of the light incident on the LDR. By the features is as follows.

When LDR received an indirect light. It will have a low resistance that causes a current flow through too much or through to ground fully. Makes a capacitor C1 look like a short circuit. As a result, the transistors Q1 and Q2 not work.

So not have a voltage pulse to trigger an SCR1(T106) or stop working so as to short-circuit the AC power. Makes electrical components, or lamps connected to the plug socket. Or the connector points SK1. Therefore not working or notice a light bulb goes out.

But when the LDR has received the sunlight. Then its body will have high resistance. Makes the current flowing through the less. So flow to store at the C1.

It has a voltage across it to use as the bias voltage to the transistors Q2(BC337) and Q1(BC327) runs. So has the voltage pulse to trigger to provide the SCR1 also works. Therefore virtual circuits are connected to the AC power. Makes the electrical components or the lamp that connected with the plug socket or the point-SK1 or noticed the lamp is lit.

Additionally, the LDR stands for the Light Dependent Resistor. Acts as a general sensor light. It is a type of resistor whose resistance value changes according to the intensity of incident light transmitted to it. If there is much light, the resistance is low, (as a result of the current through a lot).

If low light, the resistance is high, (as a result, less current flow). The sensitivity of the circuit will adjust the variable resistor VR1.

Electrical appliances or light bulbs that are connected to a plug socket or points combination with SK1 about not exceed 200 watts. Which depends on the tolerance power of diode D1, D4 or D2, D3 and SCR1. When working AC circuits to flow seamlessly through these devices, particularly the diode number 1N4007 will allow current to flow only up to about 1 amp.

Do not install the LDR to the direct exposure to the light from the lamp will turn on-off. Provides been specialized the normal bright light only. Or the back lamps, the light from the light bulbs.

Learn: How SCR circuit works

Get Ebook: Simple Electronics Vol-03


I always try to make Electronics Learning Easy.

14 thoughts on “Automatic night light circuit using SCR”

  1. Despite I´mnot having tested this circuit – I´ll use the MultiSim – I think it´s imperative, in order to mantain it´s available, keep one charge connected in the proper place. Otherwise, this circuit will not work.

  2. I forget to make mention, that, once a charge connected, it will make a serial circuit between the bridge rectifier and other part of circuit. Besides, this procedure will make a little volage drop, but, even so, its will be good enough to produce the desired effects.

  3. Has anyone tried this circuit?

    Since the load (lamp) is connected in series with a bridge rectifier, once the SCR is triggered at night and turns on the lamp, the lamp will stay on forever.

    The simplest way for it to work properly is to replace the bridge rectifier with only one diode (half-wave rectified) so that the lamp will only run on positive cycles.

  4. What kind of plug is suitable if I want to directly connect this circuit to a wall socket since the voltage is 220V? And how is the process done? Please help. Beginner for Electronics System.


Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.