The Running LEDs

This circuit is a fun light-project where you have 10 lights «running» along a line.

Pin 3 of the 555 timer has a voltage that goes on and off repeatedly as you’ve seen in some of the previous projects. This signal is connected into pin 14 of the 4017 IC. The 4017 IC counts each time the voltage on pin 14 goes from low to high. It has 10 outputs that represent how many times the voltage has gone from low to high (0 to 9). For example, after 3 counts, output Q3 goes high, while the others are low. On the 10th count, the counter starts from 0 again.

The running speed is set by R1, R2, and C1. Change one of the values, and the running speed of the lights will change.

This is a large circuit, and it’s pretty easy to connect a wire or a component in the wrong place. I suggest connecting only the 555 timer part first and adding a 470-ohm resistor in series with an LED between the output on pin 3 and minus. You should see the LED blink really fast. When you see this, you can disconnect the LED and resistor, and continue to connect the 4017 part of the circuit.

Look over your connections a couple of times before connecting the battery.

Click here for the pinout of the 4017 IC.

Here’s a video of the circuit I built:

The Circuit Diagram

Part Value Note
R1, R2 10 kΩ
R3 470Ω
C1 4.7 μF
L1 to L10 LED Standard light-emitting diode
U1 NE555 555 Timer IC
U2 CD4017B 4017 Decade Counter

Are You Stuck?

Let me know your questions and comments in the comment field below

Comments on The Running LEDs

  1. Elias says:

    Hey,

    I got the circuit working but the LED’s have a constant flicker when they’re not lit up. I tried with different LED’s and it’s now less obvious, is the flicker just dependent on different LED’s resistance?

    Great tutorials by the way, thank you!

    1. Oyvind Dahl says:

      Hey Elias,

      Hmmm. I haven’t seen any flicker myself. Is the circuit behaving as normal otherwise? Only one LED lighting up at them, time? For how long time is each LED on in your circuit?

      Best,
      Oyvind

  2. Casper B says:

    What is the last 470 ohm resistor used for, i do not see the purpose since it is only connected to ground

    1. Oyvind Dahl says:

      It’s there to set the current that flows through the LEDs:
      https://www.youtube.com/watch?v=zWC_AiycHbo

      Best,
      Oyvind

  3. George Bauer says:

    I saw your video, it looks like only 1 led is lighted at any time. That is what iI need times. I Will use 6 power supplies so as toNOT overload them. What i need is to trip the next unit and so on. Which pin on the prvios cat to Start the next cat? George

    1. Oyvind Dahl says:

      Hey George,
      The pins out from the 4017 is the trigger for each light. The trigger that makes the next light turn on is the input pin of the 4017, pin 14.

      Best,
      Oyvind

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