This is a device for testing network cables (RJ45) and telephone cables (RJ12 / 11), made with normal components (the most complicated is the LED bar). It can be supplemented with more 1N4148 diodes in anti-parallel welding under the LEDs (2, 5..9) to allow to check all cable faults.
Based on 555 as an astable oscillator, and a Johnson counter.
Details
Designed with THT components, so it can be used as a soldering exercise. It has become a small tool for students in the cycle of electrical and automatic installations.