LAN cable tester
In our hospital we often have problems with computer network cables. Cables tear because of poor material quality or bad installation or were gnawed by animals. The new installed cable then does not work because the crimped plugs do not have contact or the sequence of the wires are wrong.
With the following small tester we can now easily check LAN network cable (RJ45, RJ11) for continuity, short-circuit and the new assembled cables can be checked for the right sequence of the wires. The tester is also useful to identify the right cable when several identical cables exist.
The tester consists of two parts, the actual tester with the LEDs which is connected to one end of the LAN cable and a passive part, a terminating socket which is connected to the other end.
This tester is powered by a rechargeable mobile phone battery. That has different advantages:
Here in Tanzania a mobile phone battery is cheaper and easier to get than a 9 V battery.
The battery is rechargeable. Nobody has to buy a battery any more.
The battery is glued in the housing, so that nobody can take out the battery.
(Here batteries always disappear and are used for other purposes.)
Function
A network cable consists of 8 wires plus sometimes the shield. These 9 connections must be tested one after the other, otherwise a short between two wires or more can not be detected. This sequential testing is done automatically by multivibrator and a shift register. In principle the circuit is a running light with the LAN cable in between. If one wire is disconnected, the corresponding LED will not light up. If two wires have a short-circuit two LEDs light up and if wires are interchanged the sequences of the LEDs will be also interchanged.
The Timer 555 operates as a clock oscillator. The frequency is determined by C1, R1 and R2 and here it is about 1Hz. That means, the LED at the output (3) flashes every second.