Automated Lamp Using Op Amp 741 and LDR

On the occasion of this design task, an automatic lamp based on a light sensor where the system can distinguish dark and light through the LDR or Photoresistor sensor.

Supplies

1 LDR/Photoresistor
2 1kΩ resistors
1 Potentiometer/Variable resistor
2 9V batteries
1 Op Amp 741 IC
1 Diode (1N5819)
1 PNP Transistor (BC557)
1 5V SPDT Relay (hk4100f-dc5v-shg)
1 Bulb/ LED
Jumper wires
1 Breadboard

Objectives of the System

1) Help and lighten the workload of humans in the future in managing simple lamps.

2) As a solution to save power during the day because the lights will automatically turn off during the day.

3) Can be applied to street lamps and vehicle lamps.

Base Theory

The base of the circuit is an Op Amp 741 which is used as a voltage comparator here. The R1 and LDR is used as the inverting input and the Potentiometer/Variable Resistor is used as the non-inverting input for the Op Amp. The Op Amp then sends the output to the transistor where it will determine whether the relay will switch or not depending on the inputs entering the Op Amp.

Schematic

Block Diagram

Flowchart

Simulation Circuit

Place Breadboard and Connect Both Positive Rails and Negative Rails Together

Place Op Amp on the Breadboard. the Orientation of the Op Amp Can Be Seen by the Dot Being on the Left Side

Place Resistor and LDR and Connect Them to the Positive and Negative Rail on the Breadboard

Connect Them to Pin 2 (inverting) of the Op Amp. the Pins of the Op Amp Is As Seen.

Connect Potentiometer and Connect the Output Pin (middle) to Pin 3 (non-inverting) of the Op Amp. Connect the Other Two Pins to Power Rail and Ground Rail

Connect Pin 7 of the Op Amp to the Positive Rail and Connect and Pin 4 to the Negative Rail

Connect Pin 6 of the Op Amp to a 1k Resistor and Connect the Other End to Pin 2 (base) of the PNP Transistor. Connect the First Pin (collector) to Negative Rail. Transistor Pins Are As Seen in the Diagram.

Connect Diode With the Gray Stripe Facing Upwards and Connect the Top Part to Positive Rail and Connect the Bottom Part to Pin 3 (emitter) of the Transistor.

Place the Relay to the Breadboard and Connect the Top and Bottom Part of the Diode to the Coil Pin on the Relay. Relay Pins Are As Seen in the Diagram

Connect N/O (Normally Open) Pin of the Relay to the Positive Wire of the Bulb.

Connect 9V Battery With the Red Wire Connected to the COMMON Pin of the Relay and the Black Wire Connected to the Black Wire of the Bulb.

Connect a 9V Battery to the Breadboard. and Now Set the Amount of Darkness Needed to Activate the Circuit With the Potentiometer.

Youtube Video Link : Https://youtu.be/22GbMnEBXis

References

Relay diagram: https://abra-electronics.com/electromechanical/rel...

Op Amp diagram: https://www.bragitoff.com/2016/02/op-amp-741-ic-pi...

Transistor diagram: https://www.el-component.com/bipolar-transistors/b...