Fading

1. AKSHAY C
INTC1517505

2. Introduction
 In this LED based project, I will show you how to design an Up Down
Fading LED Circuit using very simple hardware. Nowadays, the usage
of LED lights is increasing rapidly because of their reduced cost and
long durability (of course their low power consumption).
 Generally, you can see various implementations like Automobile DRLs
(Daytime Running Lights), decorating houses, regular lamps,
emergency lights etc.
 One such important application is where the LED lights increase and
decrease their intensity depending on the number of persons entering
or leaving at a particular place or a room.
 This concept is called Fading of LEDs. Here is a simple circuit where an
LED slowly fades out when it is applied with some voltage.


3. Up Down Fading LED Lights Circuit
Principle
 The circuit mainly consists of a transistor and a
capacitor. Light Emitting Diode conducts in forward
bias condition i.e. LED glows only when positive
terminal is connected to the positive end and negative
end is connected to the negative of the battery.
 In this circuit, LED conducts only when the negative
terminal is grounded as the positive terminal is
applied with some voltage. When the button is
pressed, the capacitor starts charging and discharging
which causes the LED to fade up and down.

4. Circuit Diagram

5. Components Required
 Capacitor – 220μF
 Resistors
 2 X 100KΩ
 10KΩ
 39KΩ
 100Ω
 BC 548 (any NPN Transistor)
 LED
 ON/OFF switch (Push Button)
 Mini Breadboard
 5V Power Supply
 Connecting Wires


6. How to Operate Up Down Fading
LED Lights Circui
 Initially, switch on the circuit.
 Then press the button.
 You can see the LED fading up i.e. slowly its intensity increases. When a button
is pressed, voltage flows through the diode (not shown in the circuit) and it
then flows through a series of resistor having 100KΩ.
 The capacitor connected in parallel to the resistor is charged. This gives some
voltage to the base of the transistor which then starts conducting.
 Thus, voltage from collector flows to the emitter, which is connected to the
ground.
 Thus, negative terminal of the LED is connected to the ground.
 And LED slowly starts glowing, as the capacitor continuously produces the
pulses.
 When the switch is released, the LED starts slowly fading out as the capacitor is
discharged.
 Before the transistor, a resistor of 36KΩ is present so that while discharging, the
capacitor discharges through this resistor

7. Applications of Up Down Fading
LED Lights Circuit
 This can be used in the shopping malls for fading out
the lights in the places where there is no crowd.
 Fading LEDs can be used in security applications to
alert something.
 These can be used in home applications.
 These can be used in cars as indicators with some
changes.

8. THANK YOU