Simple Automatic Night Lamp Circuit using IC 555

This Simple Automatic Night Lamp Circuit using IC 555 works like smart switch for night light.

It have one special light sensor called LDR to check how much light is outside.

When night come and outside become dark the circuit turns ON the lamp by itself.

Then when morning comes and light comes back it turn OFF the lamp again.

It does all this with a small chip called IC 555 working like timer.

Circuit Working:

Parts List:

This circuit turns ON the light around 6 pm and turn OFF in morning by itself.

It work with one light sensor called LDR which sees light and dark.

Not like other LDR circuits this one have no flicker.

CFL and tube light also work fine.

It uses IC 555 timer chip for good and correct switching like a Schmitt trigger.

Main parts of this circuit are LDR and IC 555.

LDR change resistance with light.

In dark LDR have big resistance like 10 mega ohms.

In light it become very low maybe 100 Ohms.

Because of this circuit can know when light is there or not and then turn the lamp ON/OFF

LDR gives signal to IC 555 chip and this chip work as Schmitt trigger.

Inside IC 555 there are two comparators: one for threshold and other one for trigger.

These help to turn light ON and OFF as IC 555 work like bistable here.

Top comparator trip when voltage goes above 2/3 of power then bottom one trip voltage goes below 1/3 of power.

Both pins 6 and pin 2 connects to LDR and preset VR1.

In day time LDR pass more current.

Pin 6 get more than 2/3 VCC so IC gets reset and pin 2 also goes high but output of IC become low.

When it become dark LDR resistance go high with less current supply.

Pin 6 voltage goes down below 2/3 VCC and pin 2 also goes down below 1/3 VCC and the output of pin 3 also go high.

This high signal turn ON the transistor T1.

Relay connected to T1 now turns ON so that lamp get power through relay switch.

Only live wire go through relay and neutral wire stays same.

VR1 help to set how much dark is needed for light to turn ON.

Capacitor C2 keep transistor base voltage stable and it also stops relay from clicking ON and OFF

Diode D1 protect circuit from back power when transistor switches OFF.

LDR must not see the light from lamp, but puts it in place where it sees only sunlight.

Use 12V relay and follow circuit diagram for wire connections.

Formulas:

In this circuit one divider is made using LDR and potentiometer like a variable resistor.

This divider give one voltage to IC 555 pin 5 which is the control pin.

If we say Rpot is the resistance of potentiometer then we need to set some value which is called as Rpotadj and other is LDR resistance:

Total resistance (Rtotal) = RLDR + Rpotadj

Voltage at middle poin is the Vjunction where both connect:

Vjunction = VCC × Rpotadj / (Rpotadj + RLDR)

This voltage go to IC 555 pin 5 and help it to decide when to turn ON or OFF

Notes:

If we change potentiometer (Rpotadj) the Vjunction voltage also changes.

This change affect how IC 555 comparator work.

Always use resistor values that match IC 555 range between GND and VCC.

IC 555 can do many jobs like timing and switching and here it help with light sensing using LDR.

This type of divider setup gives IC 555 flexible voltage to control switching.

Test the circuit after it is build and if needed change the resistor or pot value for correct working.

How to Build:

To build a simple Automatic Night Lamp Circuit we need to follow the below mentioned steps:

• Take LDR and connect it in series with preset VR1
• One end connects to positive power Vcc.
• Join the middle point (junction) of LDR and VR1 to pin 6 (threshold) and pin 2 (trigger) of IC 555.
• Take resistor R2 220Ω and connect it to base of transistor T1 BC547.
• From pin 3 of IC 555 connect a 1k resistor R1 and red LED to ground.
• Connect pin 1 of IC 555 directly to ground.
• Pin 4 (reset) connect to Vcc as this stop the chip from resetting by mistake.
• Pin 5 connect to a small capacitor C1 0.01μF and the other side of capacitor is connected to ground.
• Connect pin 4 and pin 8 both to the positive power Vcc.
• T1 transistor collector connect to one side of relay coil.
• T1 emitter connects straight to the ground.
• Relays common (COM) terminal connects to the phase (live) wire of the lamp.
• Relays NO (normally open) terminal connect to neutral wire of lamp.
• Put diode D1 1N4007 across relay coil and anode negative connects to T1 collector and cathode positive connects to Vcc.
• This protect from back current (back e.m.f.).
• Now adjust VR1 to set how much dark needed for lamp to turn ON.
• Then give power to the circuit.
• Lamp will turn ON when it gets dark and will turn OFF when it is bright again.

Note:

• Always check wires and parts before giving power and any wrong connection may damage the circuits parts.

Conclusion:

Simple Automatic Night Lamp Circuit using IC 555 is easy and useful way to turn lamp ON and OFF by checking light around.

It use LDR and IC 555 chip.

This circuit is cheap and works well where we need lights to turn ON automatically like night lamp, street light or security light.

References:

LDR Based Automatic night lamp

Automatic Evening Lamp