This is a simple Led chaser which can be made using 81 leds and some complimentary components like resistors and some relative capacitors

By Rotating the 100k-potmeter on the pcb the blinking speed of the led changes and so the patterns vary accordingly

This is the circuit of a simple LED chaser. The LEDs lights one by one for a period of 1second and the cycle repeats giving the running light appearance. The circuit uses two ICs (one is 555) to drive the LEDs.

IC1 (NE555) is the popular timer IC wired in the Astable Multivibrator mode. Resistors R1, VR1 and capacitor C1 act as the timing components and the output pulses are available from the output pin 3 of IC1. These pulses are given to the input pin 14 of the Johnson decade counter IC CD4017. Out of the 10 outputs of IC2, eight outputs are used to drive the LEDs. The ninth output pin 9 is connected to the reset pin 15 to stop the counting. So that the cycle repeats. With the value of C1, each LED remains on for 1second. When one LED turns off, the second on turns on. This cycle repeats giving the running light appearance. Resistor R3 keeps the input pin 14 of IC2 low after each pulse.VR1 adjusts the speed of LED chasing.

Explanation of Circuit's Working:

The 555 timer IC is configured to work in astable mode. Which means, the output from the 555 timer changes continuously between high (Supply Voltage) and low (0V). In other words, if you connect an LED between the output of 555 timer and ground, the LED flashes/blinks continuously.

This pulsing output from the 555 timer is connected to the clock input of 4017 IC (a decade counter). It has 10 output pins and we have connected an LED to each output. By default, the first output pin is on/high and the rest are off. Each time the clock input pin of 4017 IC detects a rise in voltage (from low to high), it turns off the current output and turns on the next sequential output. This swapping of outputs which looks like the LED's are chasing each other, continues until the last LED and then the output resets back to the first LED.

[Watch the video at the beginning of this post for better visual understanding]

For this LED chaser circuit, we have used all the 10 outputs of 4017 IC. But if you wish to make an LED chaser circuit with less than 10 LED's, you can do the same by connecting the LED's starting from U0. Let's say you wish to build this circuit with 4 LED's, you need to connect an LED to each of U0, U1, U2, U3 and leave the rest.

LED D1 is used to indicate the output of 555 IC and the resistor R3 is for current limiting.

Similarly VDD (16th pin) and VSS (8th pin) of the CD4017 IC is connected directly to the power supply. Clock enable (13th pin) is an active low input, so it is connected to ground. Clock input (14th pin) is connected to the output of 555 timer. Each decoded output pins (Q0 ~ Q9) is connected to LED. Resistor R3 is used for current limiting. Only one resistor is required for limiting current through all LEDs since only one LED will turn on at a time.

You can easily understand the working of the circuit from the above animation. As I explained above, 555 timer is wired as an astable multivibrator. Please read the article Astable Multivibrator using 555 Timer for detailed explanation. So the 555 will produce square wave output and which will act as a clock for the CD4017 counter IC.

You can see that for each high pulse output of 555, the output of 4017 is incrementing by one. Output frequency of 555 astable is given by the following equation.

Output Frequency = 1.44/((R1 + 2RV1) * C1)

So you can easily change the output frequency of above circuit by varying the preset RV1. By this we can change the LED chasing speed.

Tip

You can make use of Reset input (15th pin – MR) if you want to reduce the number of LEDs. Just connect the output pin to the reset pin as shown below. For eg. if you need only 2 LEDs, you can connect Q2 (4th pin) to Reset pin.