Network cable tester

Build a network cable tester with just two cheap integrated circuits and a few parts from the ‘junkbox’.
This cable tester, tests all the 8 wires in a network cable in one move, if one of the 8 LEDs does not lit up, it means that the wire corresponding to that LED is faulty.

You need:

  • 1 x 4017 decade counter,
  • 1 x 555 timer,
  • 8 x LEDs,
  • 2 x 8P8C modular connector (RJ45),
  • 8 x 100Ω resistor,
  • 1 x 10KΩ resistor,
  • 1 x 15KΩ resistor,
  • 1 x 4,7µF capacitor.


The yellow LED has no special significance, I only had 7 green LEDs.

A good ideea would be that every LED have the color of the corresponding wire, and maybe a switch for the T568A and T568B standards.


  1. written by: Ashish Adhikar on August 17, 2018 at 7:21 am - Reply

    Do u have a demo video?
    Do the all light up at once or they just go one by one?

    • written by: Mihai on August 21, 2018 at 2:58 pm - Reply

      Sorry, i don’t have a video.
      They light up one by one. The frequency can be adjusted by changing the values of the capacitor and resistors in the 555 circuit.

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