Introduction: LED Chaser

About: I am electronics and robotics enthusiast and love making new and innovative things everyday!

Hello everybody! I'm back with another instructable about making an LED Chaser. It's a super simple project based on the 555 timer and the 4017 decade counter. It works incredibly well and it's quite easy. So let's get started!

Step 1: First, a Bit of Theory

The 555 timer IC is an integrated circuit (chip) used in a variety of timer, pulse generation, and oscillator applications. The 555 can be used to provide time delays, as an oscillator, and as a flip-flop element. Derivatives provide up to four timing circuits in one package.

The IC 555 has three operating modes:-

  • Bistable mode or Schmitt trigger : the 555 can operate as a flip-flop, if the DIS pin is not connected and no capacitor is used. Uses include bounce-free latched switches.
  • Monostable mode :in this mode, the 555 functions as a "one-shot" pulse generator. Applications include timers, missing pulse detection, bouncefree switches, touch switches, frequency divider, capacitance measurement, pulse-width modulation (PWM) and so on.
  • Astable mode : This project uses the 555 timer in the astable mode. The 555 can operate as an electronic oscillator. Uses include LED and lamp flashers, pulse generation, logic clocks, tone generation, security alarms, pulse position modulation and so on. The 555 can be used as a simple ADC, converting an analog value to a pulse length (e.g., selecting a thermistor as timing resistor allows the use of the 555 in a temperature sensor and the period of the output pulse is determined by the temperature). The use of a microprocessor-based circuit can then convert the pulse period to temperature, linearize it and even provide calibration means.

In order to understand the working of IC CD4017, one must know about its individual pins. It has 3 input pins, 10 output pins, one ground pin, one for the positive voltage supply and one for carry out pulses. Pin diagram of CD4017 is given in the pictures above.

Input pins

  • Reset pin (pin 15) - It is used to reset the counter to zero. For instance, if you want the counter to count up to third output then connect the fourth output to pin 15. Now after every third output, it will automatically starts counting from zero.
  • Clock pin (pin 14)- Whenever pin 14 goes high, it provides the output. Like, for first clock pulse pin 3 will provide you output; for next pulse pin 2 will provide output and so on. After 10 pulses it will again start from Q0 output.
  • Clock Inhibit pin (pin 13)- It is used to switch the counter "on" and "off". When you want to switch off the counter, then pin 13 should be high. If it is high, it will ignore the clock pulse no matter how many times you press the switch meaning the counter will not advance.

Output pins (pins Q0- Q9)- It is used to receive the output in sequential manner. Like for first pulse pin 3 will provide you the output and so on.

Ground pin (pin 8) and Positive Voltage Supply pin (pin 16)- They are used to provide the ground connection and the positive voltage supply to the IC.

Carry out pin (pin 12)- It is used to connect one or more 4017 ICs. The carry pin of first 4017 is connected to clock input of second and the carry pin of second is connected to the clock input of third and so on. In our circuit we have used only one IC that's why we have left this pin.


Step 2: Gathering the Parts

Tools required

Solder Iron

Solder wire

Wire stripper

The following parts are required to build this project:

LEDs (any color you like) X 10

SPST Switch

9v Battery

9v Battery Connector


Breadboard Wire

Potentiometer - 10K Mono

Potentiometer Knob

Diode - 1N4007


-1 uF




- For LED (Any value between 1K and 22K should work.)



IC Base

- 8 Pin

-16 Pin


-555 Timer

-4017 Decade Counter

Step 3: The Schematic

Follow the schematic and build the circuit. I recommend you to first prototype the circuit on a breadboard.

You can experiment with different values with the capacitor between pins 2 and 1 of the 555 timer.

The resistors between pin 8 and 7 , and pin 7 and 6 can also be substituted as desired.

Step 4: Building the LED Chaser

Build the circuit on a perfboard (you may etch your own PCB for this project if you like). Just be a bit careful about unwanted solder joints and run a hobby knife between them after you have soldered everything. You may assemble the Potentiometer and switch on the perfboard like me ; but you can go for an electronics enclosure or something similar.Testing the

Step 5: Testing the Circuit

After building the circuit plug in the battery and turn on the switch. IF you are successful, then all the LEDs should light up in a sequence. If, however it is not working then immediately turn off the circuit. The decade counter ic is pretty delicate and a wrong connection could easily destroy the IC. Check all the connections and solder joints ; melt and again solder all dry solder joints.

Well this is all you need to do for this project. All comments and suggestions are welcome.

Thanks and Have a Nice Day!

Full Spectrum Laser Contest 2016

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Full Spectrum Laser Contest 2016