How to Make LED Chaser Circuit With 555 Timer and CD4017

LED chaser circuits — also called running light circuits — are classic beginner electronic projects that produce a captivating light pattern where LEDs light sequentially. This “chasing” effect appears as though light is moving across an array, and it’s perfect for learning basic digital electronics, timing circuits, and integrated circuit wiring.

In this project, you’ll build an LED chaser using two popular integrated circuits: the NE555 timer IC configured as an astable oscillator and the CD4017 decade counter IC that controls the sequence of LEDs.

What Is an LED Chaser Circuit?

An LED chaser circuit is an arrangement of LEDs that light up one after another in sequence. This creates a visual effect similar to chasing lights — used commonly in electronic decorations, art projects, running light displays, and even automotive LED bars.

In our design:

• The 555 timer acts as a clock generator, producing regular square wave pulses.
• The CD4017 decade counter receives these pulses and advances its output each time it gets a new clock signal.
• Each output of the CD4017 is connected to a single LED.
• With every incoming clock pulse, the next LED lights up and the previous one turns off, creating a chasing effect.

What You’ll Need (Components List)

Here’s a typical list of components you’ll use:

Component	Quantity
NE555 Timer IC	1
CD4017 Decade Counter IC	1
LEDs	10
220 Ω Resistor ∕ LED	10
Potentiometer (approx. 50 kΩ)	1
Fixed resistor 1 kΩ	1
Capacitor 10 µF	1
Capacitor 0.1 µF (104)	1
Breadboard & Jumper Wires	—
9 V Battery & Connector (or 5 – 12 V PSU)	1

💡 You can adjust the number of LEDs by using only some outputs of the CD4017, or cascade multiple counters for more than 10 LEDs.

How the Circuit Works

555 Timer in Astable Mode

The 555 timer is configured as an astable multivibrator, meaning it continuously oscillates between high and low output states. The output at pin 3 produces a square wave — a rapid on/off signal — whose frequency is determined by:

• the potentiometer (used for speed control),
• and the capacitor in the timing network.

This output becomes the clock pulse that drives the CD4017 counter.

CD4017 Decade Counter Sequencing

The CD4017 is a 10-stage counter. Each incoming rising clock edge from the 555 timer advances the counter by one step. Only one of the ten outputs is HIGH at a time:

1. The first clock pulse lights LED1 (through Q0).
2. The next pulse lights LED2 (through Q1).
3. … and so on until LED10 on the tenth pulse.
4. The counter then rolls back to Q0 and the cycle repeats.

Two important CD4017 pins:

• Pin 14 (Clock) — receives pulses from the 555.
• Pin 15 (Reset) — usually tied LOW so the sequence isn’t interrupted.

Wiring the Circuit — Step by Step

Below is a step-by-step guide to assembling the circuit on a breadboard:

Step 1: Place the 555 Timer

• Insert the NE555 IC into the breadboard.
• Connect pin 1 to ground (GND).
• Connect pin 8 to VCC (positive rail).

Step 2: Build the Timing Network

• Connect the fixed resistor and potentiometer between pins 6 and 7 of the 555.
• Place the electrolytic capacitor (10 µF) from pin 2 (trigger) to ground.
• A small 0.1 µF cap goes from pin 5 (control) to ground to reduce noise.

Step 3: Connect the Clock Output

• Run a jumper from pin 3 (output) of the 555 to pin 14 (clock) of the CD4017.

Step 4: Wire the CD4017 Outputs

• Insert the CD4017 into the breadboard.
• Connect pins 8 and 16 to ground and VCC respectively.
• Tie pin 13 (clock enable) and pin 15 (reset) to ground for normal operation.
• From outputs Q0–Q9, connect each LED through a 220 Ω resistor to ground.

Step 5: Power Up and Test

• Connect your 9 V battery or regulated power supply.
• Turn the potentiometer — the LEDs should light one after another in sequence.

Adjusting and Troubleshooting Tips

Speed Control

The potentiometer in the timing network lets you change the speed of the chasing effect:

• Higher resistance = slower clock pulses → slower LED sequence.
• Lower resistance = faster pulses → rapid chasing.

Common Issues & Fixes

Problem	Likely Cause	Fix
LEDs don’t light	Power or ground miswired	Check battery polarity & rails
All LEDs on at once	No current limiting	Add resistors to each LED
LEDs skip or don’t sequence	Clock signal not reaching	Verify 555 outputs and CD4017 clock pin wiring

Where You Can Use an LED Chaser

LED chasers aren’t just fun projects — they’re practical for:

• Decorative lighting & art installations
• Lighting effects for costumes or vehicles
• Status indicators in DIY electronics
• Learning digital logic and timing fundamentals

Expand the Project Ideas

Once you’ve built your first chaser:

✨ Add more LEDs using a second CD4017 chained to the first.
✨ Use RGB LEDs for color chasing effects.
✨ Swap in microcontrollers for programmable patterns.
✨ Mount it on a PCB for a permanent installation.

Conclusion

Building an LED chaser circuit with a 555 timer and CD4017 is a classic beginner project that reinforces understanding of oscillators, counters, and sequential logic. With a few components and simple wiring, you can create dynamic lighting that’s useful and fun — and a great stepping stone toward more advanced electronics.

Frequently Asked Questions