Simple Automatic Day Night Switch Circuit

Electricity saving is important particularly in urban areas where there is a shortage.

This article demonstrates how to construct a simple automatic light switch that activates and deactivates devices based on the outside light level.

One can lower your electric bill by doing this.

What is a Automatic Day Night Switch Circuit:

An automatic day night switch circuit sometimes known as a light sensitive switch or evening light switch is made to automatically turn on a load at night or in low light and than turn them off during the day or in bright light.

Outdoor lighting, streetlights and other applications need automatic light control depending on the outside environment which usually use this kind of circuit.

Circuit Working:

Parts List:

The circuit uses two transistors Q1 and Q2 and an LDR.

When light falls on the LDR the increased resistance causes Q1 to turn on activating the relay.

As a result in the absence of light Q1 transistor turns off deactivating relay.

This dynamic switching mechanism allows for the effective control of various appliances during day and night cycles.

One can assist in a collective effort to save electricity by implementing this simple automatic day night circuit which is important in solving the problems of todays energy demands.

Formulas:

Light Dependent Resistor LDR Resistance:

R_LDR ∝ 1 / I_LDR

where:

• R_LDR​ is the resistance of the LDR.
• I_LDR​ is the current flowing through the LDR.

Transistor Q1 Activation Threshold:

V_T1 = V_BE1 + I_LDR × R_LDR

where:

• V_T1​ is the threshold voltage for Q1.
• V_BE1 is the base-emitter voltage for Q1.

Transistor Q2 Activation Threshold:

V_T2 = V_BE2 + ( V_CC − I_LDR × R_LDR )

where:

• V_T2​ is the threshold voltage for Q2.
• V_BE2​ is the base emitter voltage for Q2.
• V_CC​ is the supply voltage.

Relay Activation Time Constant:

τ = R_Relay × C_Relay

where:

• R_Relay is the resistance of the relay coil.
• C_Relay is the capacitance of the relay.

Note:

The connections between the circuits resistance, current and voltage thresholds are made clear by these formulas.

Based on these calculations simple automatic day night circuit components like the variable resistor is adjusted to fine tune sensitivity and improve efficiency in connection with certain atmospheric conditions.

How to Build:

Follow the below mentioned steps for building a Simple Automatic Day Night Switch Circuit:

• Collect and arrange all necessary items on a cleaned work surface.
• When choosing resistors, capacitors and diodes make sure they match the circuit parameters.
• Connect the circuit with the LDR.
• The states of Q1 and Q2 are affected by variations in the LDRs resistance when the ambient light fluctuates.
• The circuit should be connected to NPN transistors Q1 and Q2.
• During the day Q1 transistor activates the relay and at night Q2 takes over.
• Check the correct connection between the relay and the right side transistor.
• This configuration makes it possible to properly turn on and off the desired appliances during the day night cycle.
• Adjust the circuits sensitivity by adding a 100k variable resistor.
• Measures are taken to get used to certain environmental circumstances.
• Connect the circuit to a 5V to 12V DC battery making sure that the operational voltage selected matches the relay specifications.

References:

DESIGN AND CONSTRUCTION OF AN LDR 

Design and Analysis of Image as a street light switch