Dark-detector LED

The heart of this project is a photoresistor. A photoresistor is a type of resistor with resistance varying according to the light that strikes its surface. The project’s result is a LED which is automatically turned on when the lights go off.

Objective

The project is an introduction to photoresistors.

  • You see how breadboards, resistors, photoresistors, transistors and LEDs look like .
  • You understand how breadboard works.
  • You understand the difference between schematic and real circuit.
  • You understand that sensors are input devices.
  • You understand what a photoresistor does.
  • You can notice a role for transistors.

The Schematic

This is the circuit of the project.

project-dark-detector-led-schematic

On breadboard

project-dark-detector-LED_bb

You can see a way to set up the circuit on the breadboard. Remember, there are many correct ways to transfer a circuit on the breadboard.

Notes

  • The transistor works as a variable resistor controlled by current. It lets current to pass from collector to emitter according to the current that flows from base to emitter.