Inspiration

While studying photoresistors in our college and had an experiment where plotting the graph of resistance vs intensity of light falling on a photoresistor or LDR(light dependent resistor), we started thinking of this project, where we can turn on and off the street lights automatically. Simple yet powerful project.

What it does

It basically controls the switching of street lights automatically. After dusk, it switches on the street lights, and while dawn it turns it off automatically. Since every place does not incur exact same dawn and dusk behaviour, the sensitivity of the circuit can be manually changed as required, so that it can perfectly fit in the operating environment.

How we built it

The circuit consists of a comparator, for which we have used an LM358 opamp ic. To control and sense the intensity of light(after dusk the intensity drops and after dawn the intensity grows) we used an LDR. The LDR with a 10k resistor forms a potential divider and the voltage gets feed to the non-inverting terminal of the comparator. To change the sensitivity we used a potentiometer to vary the voltage going to the inverting terminal of the comparator. Two LEDs were connected to the output of the comparator indicating the street lamps. And the circuit is done. To build the model of the street, cardboard was used and painted black. Pasted few white strips of paper to make it look like a real road. The street lamps were built using yellow LEDs and the headcover was built using a blister pack (medical tablets cover), to give it a more street lamp feel and also to diffuse the light. With help of straws and paper, the pole of the lights was built. Finally, to power it up, a 3.7v Lion battery was used.

Challenges we ran into

Building the model was quite tough. While testing the circuit in a breadboard, due to loose connection, the output of the circuit was going high unconditionally, and that troubleshooting took a while. Again while connecting the wires of the LEDs, the wires came short and were very troublesome to solder them properly. And finally putting it all together on a perfboard and building the circuit was a bit challenging.

Accomplishments that we're proud of

Making the circuit work as desired on the breadboard was the 'Yaay' moment. Finishing soldering the circuit on the perfboard was indeed a great accomplishment. Making the model of the street and finding a way to make the cover of the street lamps by recycling the medical tablet covers was great.

What we learned

We learned how photoresistors work as we got to implement them in real life, which we learned as a theory in semesters. We learned about comparators, and how to use an op-amp as a comparator, also got to know that the open-loop gain of opamps is very high, thus they act as the comparator in an open-loop configuration. Again we read about potential dividers, but we implemented that here to know what exactly it is.

What's next for Automatic Streetlight

Thinking of improving the comparator circuit to a Schmitt trigger configuration to prevent high-frequency switching while the transition of dusk or dawn. Adding a driver circuitry to drive relays, that can drive the actual street lamps. And that would be good to go for implementing them in real streets.

Entertainment

After I completed the project model, at night it worked as a night-lamp for my room. The model is very convenient for utility and entertainment purposes because it automatically lights up when the room is dark and the lights also switch off when the room is lit, one can easily build this model for the sole purpose of creating a cool night-lamp for their room.