simple RJ45 cable tester

The RJ45 cable tester verifies the continuity of the son, the absence of short circuit and the respect of the order of the son.

Diagram of RJ45 cable tester (transmitter part):

The oscillator is based on a 4011. Its period of oscillation here is the order of seconds to allow time to see the LED light up in succession! The output is taken from pin 11.

The heart of the tester is a 4017 (Johnson counter). It has 10 outputs that pass at high voltage ("1") one after another, each clock edge. There is only one output to "1" at a time, the others being the low level "0". Of the 10 out of 4017, it uses only 8 to RJ45 cable to be tested.

The supply voltage must not exceed 15V.
The numbers from 1 to 8 are not in order. Thus, the 4017 paperback is internally. This is surprising but true!

Diagram of RJ45 cable tester (receiver part):

The numbers 1-8 are the pins of the RJ45 socket. the receiver is connected to the other end of RJ45 cable.

Operation of the cable tester RJ45

Imagine that the pin number "5" is in the high state. The current flows from pin 5, through the resistance 680 ohms, the corresponding LED, and returns to other terminals through the diodes 1N4148
If a wire is cut, the corresponding LED will not turn over

Setting up the test RJ45 cable:

Connect the transmitter on one end of the RJ45 cable to be tested, the receiver on the other end.
If all the LEDs light in sequence, the wiring is correct in càable RJ45.
If a wire is cut, the corresponding LED never light.
If son is 2 short-circuit, two LEDs light up simultaneously.
If the order of the son is not respected, the LEDs do not flash in order (can also test a crossover cable).