A Light emitting diode (LED) is essentially a pn junction diode. When carriers are
injected across a forward-biased junction, it emits incoherent light. Most of the
commercial LEDs are realized using a highly doped n and a p Junction.
Generally LED is simple , but if we add just Arduino Uno3
without any electronic component we can use it for security for example when it's detect light in dark , anyway we can use this idea in much. it will work like Ultrasonic send waves and if a object in domain waves, will turn on alarm.
2 LED // LED1 Receive Light (input) and LED2 (Output)