A Chaser Circuit consists of a clocked IC or other electronic unit like an Arduino that drives an array of LEDs in such a way that individual LEDs (or small groups of LEDs) turn on and off in a predetermined and repeating sequence producing a visually attractive pattern. In this tutorial I am going to create a chaser circuit that can drive 20 or more LEDs using 555 timer IC and CD4017 decade counter. Watch this video for detailed step by step instructions on how to build this circuit and for a complete instruction on how the circuit works. 

Components Required

For this tutorial we need:

• 1 x NE555 Timer IC
• 2 x CD4017 Decade Counters
• 1 x 10K Resistor
• 1 x 1K Resistor
• 3 x 220E Resistors
• 1 x 33mfd Capacitor
• 2 x 2N2222 NPN Transistor
• 21 x LEDs
• 1 x Custom Built PCB or Breadboard

How This Circuit Works

The circuit is very simple. The 555 Timer IC operates as a clock oscillator or clock generator. The signal from the 555 IC clocks the 4017 decade counter. Output from PIN-3 of the 555 timer IC is given as an input to PIN-14 of the 4017 IC. Whenever a pulse is received by the 4017 IC, the counter increments the count and activates the corresponding output PIN (Q0 to Q9) causing a shift. This IC can count upto 10.
To know more about the ICs please check out my tutorial no. 26 "555 Pulse Generator Module, How it Works", the link is in the description below.

Now, to flash more than 10 LEDs (upto 100) we need to connect a 2nd decade counter to this setup. The Carry Out pin (CO) PIN-12 of the 1st 4017 IC connects to the clock input pin PIN-14 of the 2nd 4017 IC.
The Carry Out pin goes from LOW to HIGH when the counter of the 1st IC reaches 10. By connecting this pin to the clock input of the 2nd decade counter, we can count numbers higher than 10.

In my first setup, I am flashing the same 10 LEDs using the 2 decade counters. The Q0 PIN of the 2nd IC is connected to a NPN transistor. A small input current at the Base of the transistor allows much higher current to flow between the Collector and Emitter. The Q1 PIN of the 2nd 4017 IC is connected to the RESET pin (PIN-15). By connecting Q1 to the RESET pin we stop the 2nd IC from counting further up, resetting itself and sending the control back to the 1st IC.

Now, to add another lot of 10 LEDs we just need to move the RESET pin from Q1 to Q2 and connect the common cathode of the second lot to pin Q1 via a transistor. The anodes connect to the 1st IC exactly the same way the 1st lot of LEDs are connected.

You can continue adding LEDs to the 2nd IC just by moving the RESET pin to the next corresponding pin and connecting the anodes to the 1st IC. To change the speed of the LEDs go ahead and change the capacitor to a higher or lower value.

Bread Board Demo

Before designing the PCB, I tested the circuit and its logic on a breadboard.
Setting up 20 LEDs on a breadboard along with other components, made the board way too crowded. So, this is the 555 timer IC generating the pulse and these are the two 4017 ICs that will run the chaser circuit.
Firing up the circuit, lights up the LEDs and the LEDs appear to chase each other. Bingo, everything works as expected.

The Board Design

Using an EDA I designed the circuit board for this project. The board has 3 sections. Starting from left to right the 1st section is for powering up the board using a female MicroUSB socket. The 2nd section generates the clock pulse using the 555 timer IC. The 3rd section is for the 4017 ICs and for connecting the cluster of LEDs. To create a chaser effect using 10 LEDs, we need to solder one NPN transistor and one 100E/200E resistor in the No.1 sockets of the board. Then we need to connect the RESET pin to terminal number 1. After that, connect the +ve terminals of the 10 LEDs to the bottom "LED Array" and then go ahead and solder all their -ve terminals together. After soldering the -ve terminals, solder this junction to pin number 1 of the "Common Cathode LED Array". That's it as simple as...