Lights and Display Board Circuits

UP/DOWN Fading LED Lights


  • Introduction 
  • Up Down Fading LED Lights Circuit Principle
  • Up Down Fading LED Lights Circuit Diagram
  • Components Required
  • Up Down Fading LED Lights Circuit Design
  • Link to Circuit Simulation Video
  • How to Operate Up Down Fading LED Lights Circuit?
  • Link to old Project Output Video
  • Applications of Up Down Fading LED Lights Circuit
  • Limitations of the Circuit


I’ll show you how to make an Up Down Fading LED lights Circuit utilising extremely basic hardware in this LED-based project. Because of their low cost and long lifespan, LED lights are becoming increasingly popular (of course their low power consumption).

Various implementations can be seen, such as automobile DRLs (Daytime Running Lights), decorating houses, normal lamps, emergency lights, and so on.

One key application is when the intensity of LED lights changes in response to the number of people entering or leaving a specific location or room.

Fading of LEDs is the term for this notion. Here’s a simple circuit that progressively fades an LED.

Up Down Fading LED Lights Circuit Principle

A transistor and a capacitor are the main components of the circuit. The forward bias condition is when the positive terminal of the LED is connected to the positive end of the battery and the negative terminal is linked to the negative end of the battery.

Because the positive terminal is connected to a power source, LED conducts only when the negative end is grounded. The capacitor begins charging and discharging when the button is pressed, causing the LED to fade up and down.

Up Down Fading LED Lights Circuit Diagram

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

Up Down Fading LED Lights Circuit Design

The power supply is connected to the On/Off switch, which is a push button, in this circuit. To put the button in the pull-down mode, a 10K resistor is attached after it. This causes the button to be low at first, but when pressed, it becomes high.

The switch is then linked to a 100K resistor, which is in charge of charging the 220F capacitor. Before the transistor, a 39K resistor is connected, through which the capacitor discharges.

A 100K resistor is connected in parallel to the capacitor, allowing the 39K Resistor to discharge the majority of the charge.

The transistor employed here is a BC548 series NPN transistor. This NPN transistor is in the off state at first, meaning it will not conduct. Only if the base area is applied with voltage does voltage pass from emitter to collector. The transistor’s base voltage must be at least 0.7 volts.

When this voltage is supplied, the transistor begins to conduct and current flows from the emitter to the collector. You may learn more about NPN Transistors by reading the following article: Transistor Biasing and Characteristics.

Between the 100K Resistor and the capacitor, a PN Junction Diode such as the 1N4007 can be used to ensure that when the capacitor is discharged, the charge only passes through the other resistors.

Fading LED Lights

How to Operate Up Down Fading LED Lights Circuit?

  1. To begin, turn on the circuit.
    2. After that, press the button.

3. The LED appears to be fading up, indicating that its intensity is gradually increasing. When you press a button, voltage goes via a diode (not illustrated in the circuit) and then through a series of 100K resistors.

4. The parallel capacitor connected to the resistor is charged. This provides a voltage to the transistor’s base, which subsequently begins to conduct.

5. As a result, voltage from the collector travels to the emitter, which is grounded.

6.Thus, negative terminal of the LED is connected to the ground.

7. As the capacitor continues to create pulses, the LED gradually begins to illuminate.

8. As the capacitor is exhausted, the LED progressively fades out when the switch is released.

9. A 36K resistor is present before the transistor, so that the capacitor discharges through this resistance while discharging.

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.

Limitations of the Circuit

  • LED lights should be powered correct voltage otherwise they may be damaged.
  • LEDs can change color due to age and temperature.

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