Comprobador de Cable de Red Rj45

7/27/2019 Comprobador de Cable de Red Rj45

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Do-it-yourself

LAN Cable Tester

created by Frank Weithner

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 becausethe crimped plugs do not have contact or the sequence of the wires arewrong.With the following small tester we can now easily check LAN network

cable (RJ45, RJ11) for continuity, short-circuit and the new assembledcables 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 isconnected 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 getthan 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.)

FunctionA network cable consists of 8 wires plus sometimes the shield. These 9connections must be tested one after the other, otherwise a short

between two wires or more can not be detected. This sequential testingis done automatically by multivibrator and a shift register. In principle


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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 havea 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, theLED at the output (3) flashes every second.


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The signal clocks the decade counter divider 4017. The result is, thatthe outputs are switched sequentially from low to high. Output 9 (11) is

connected to Reset (15) so that the counter starts again from the

beginning when reaching output 9. Note that only the active output has

high signal while all the others are low, that means ground potential.Now the tricky part. Let's say output 1 is high. The current now flowsthrough the series resistor and LED 1 (the diode parallel is in reverse

direction and has no influence), through our network cable and thentrough all other wires back to the tester, because all other outputs now

have ground potential and all other parallel diodes are now in forwarddirection. That also explains why all pins of the termination socket are

connected together.

BatteryThis version is made for a 3.7 V mobile phone battery. A mobile phonebattery has several advantages: It is cheap, easy to get, it is

rechargeable because it is permanently installed in the housing and

delivers an unusual voltage nobody takes it out and uses it for otherpurposes.

You can take any battery, as long the voltage is higher than 3.0 V.Below this voltage the ICs do not work any more.

A common 9 V battery can also be used but then all series resistors forthe LEDs have to be changed from 47 to 470 .

For charging the battery you can take any (mobile phone) charger aslong the output voltage is higher than the voltage of the battery.

I charge my device via an USB cable (because computers here do notdisappear as often as a mobile phone chargers...). You can take whatyou can get, but the charging resistor should be adapted to the chargervoltage and the battery.

According to Ohm's law the calculation is the following:

Resistor = voltage drop across the resistor / current through

the resistorR = (Vcharger - Vbattery) / charging current

The charging current should be 1/10 of the battery capacity that

corresponds to 12 hours of charging. My battery has 700 mAh. Thatmakes 70 mA charging current.


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R = (5 V - 3.7 V) / 0.07 AR = 18.6

The next possible resistor is 18 . I only found a 22 . No problem, Iwill charge a little longer.

But how about the wattage? Is a W resistor big enough?

P = Vresistor x IP = 1.3 V x 0.07 A

P = 0.09 W

Yes, the smallest resistor can be taken.

Assembling

The construction in principle is easy. A PCB is not needed, a dot matrixboard is enough. The LEDs can be glued directly in the lid of the

housing, the series resistors and the reverse diodes are soldered directlyto the LEDs.


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The assembling gets easier, the bigger the enclosure is. Mine is almosttoo small. For the ICs better take sockets. LEDs, charge socket and

battery are glued in the housing with two-component adhesive. Also thepins of the terminating socket I have sealed with two-component

adhesive.

Links and sources

For more information about RJ45, RJ11, LAN cable atwikipedia.

Heremy calculator for Timmer 555 applications.
http://en.wikipedia.org/wiki/Modular_connectorhttp://en.wikipedia.org/wiki/Modular_connectorhttp://en.wikipedia.org/wiki/Modular_connectorhttp://frankshospitalworkshop.com/electronics/timer_555_calculator.htmlhttp://frankshospitalworkshop.com/electronics/timer_555_calculator.htmlhttp://frankshospitalworkshop.com/electronics/timer_555_calculator.htmlhttp://en.wikipedia.org/wiki/Modular_connector

Comprobador de Cable de Red Rj45

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