manual - ethernet cable tester

SSPJI02: Ethernet Cable Tester

Salvage Server Project 'Junk Ideas' 2:

Ethernet Cable TesterProduced by the Free Range Salvage Server Project, November 2003http://www.fraw.org.uk/ssp/

Making Ethernet cables is easy, when you have the tool to crimp theconnectors. But even then, you can't always be sure that the connector has been properly connected to the cable. Commercial network cable testers cancost £60 or more. Here's an idea for a simple cable tester that cost under £20 ifyou, or someone handy with a soldering iron, makes it from scratch.

The theory of the project

This project is a simple continuity tester – but paralleledeight times to check each of the wires in the Ethernetcable. It's just a battery and a bulb (well, light emittingdiode – LED) that shows you have a good connection onyour connector.

It would be very easy to produce the sort of professionalcable testers that cost £60 to £80. But we've designed asimple project that can be put together with minimal effort.

To save on cost you could build this completely fromscrap. The only problem that you're likely to have is findingthe RJ-45 sockets to plug you cable into. They're actuallydifficult to buy as single sockets. So you'd have to takeapart some old network cards, or a broken hub, to get holdof them. Then you have to find a box to put all the parts in.So instead we've solved these two problems in one byusing a double network wall socket. You can sometimes

find these in junk sales. Otherwise you can buy them.

The other four significant parts are:� A set of 8 dual in parallel – or DIP – switches. These

can be recovered from old computer equipment. They'reespecially common on old ISA PC cards because theyare used to configure the card. We've stuck ours into a16-pin dual in line – or DIL – socket. This not onlyensures we don't damage the switches when soldering,but it also means we could reuse the DIL switches if weever needed some for another project.

� A set of LEDs to indicate whether the wire in the cableworks when under test. We could have used old LEDs,but instead we bought some new low power LEDs to cutdown on battery usage. Old LEDs will do OK – althoughit helps if they are the same colour and size!

� A single in line array – or SIL – of resistors. Theseregulate the voltage in each cable to the correct value tolight the LEDs. These can be difficult to get hold of for aparticular resistance value, but you often find SILs ofrandom value on old computer motherboards and PCcards. In this case you'll have to measure the resistanceof the SIL to see whether it's suitable for the project.

� A battery. You could use any old 9 volt, PP3 battery.But we've used a rechargeable battery. In fact an oldrechargeable that's getting a little past it's best, anddoesn't hold charge well, but it's OK for this project.

There's a circuit diagram for the unit on the next page.

The only technical part of this project is setting the value ofthe SIL resistors. You have to calculate this value, inOhms, using:

(battery voltage – LED forward voltage) x 1000LED forward current

In this case we've used special low current LEDs. So theresistor value is [(9V – 2.5V) x 1000] / 2mA, equals 3,250

Copyleft 2003, The Free Range Network page 1 of 8


Ohms. The nearest preferred value SIL above this is 3,900Ohms, or 3.9k. So we use this value of SIL. If you reuseold LEDs, you can assume that they have a forwardcurrent of around 25mA, and a forward voltage of around2.25V, and calculate accordingly.

The other issue with LEDs is that they can only be usedone way round. The wire connected to the battery positive– the anode – is usually the longest leg on a new LED. Thewire connected to battery negative – the cathode – isusually marked by a small flat area on the small flange thatruns around the base of the LED body. If in doubt, get a2.2k resistor (or there abouts) and a 9V battery, connectthe resistor to battery positive, and then connect yourLEDs between the resistor and battery negative. When theLED is the right way around, and assuming the LED worksOK, then it will light. You can then mark the anode (wireconnected to the resistor) for later reference.

The other thing we need is hook-up wire. Use any oldlightweight wire. But for simplicity we used some oldEthernet cable. It's not because we need the Ethernetcable. It's just so that we have the standard colour-codedwires to ensure we fix the right wires to the right terminals.You'll need two 6”/15cm lengths of Ethernet cable.

We mount the components on stripboard or veroboard.Stripboard has copper strips with holes punched every0.1”/2.54mm. To mount the components on the board youneed a soldering iron and some solder (with a flux core tomake the solder easier to use). If you've never used asoldering iron before you should practice first by solderingsome lengths of wire to the stripboard. The important thingis to get small, neat blobs of solder on the board, and toensure that you don't bridge between the copper strips.

As we're using anEthernet wall socketyou also need an IDCinsertion tool – asmall plastic prodthat's usually used topush wires into theconnectors. Other-wise you'll struggle toget good connectionon the socket.

Finally, you'll need adrill bit the same sizeas your LEDs; acouple of small boltsto fit the stripboardonto the case; abattery clip; a deep,46mm back box

(short ones are no good for this job) to fit the Ethernetsocket to; and a Stanley knife and fret saw to cut the case.

Beginning construction

We begin by cutting two pieces of stripboard to the rightsize. One for the switches, which is fifteen strips by sixholes, and one for theLEDs, which is elevenstrips by four holes. Ifyou have the spareboard, it's useful tomake them a littlelarger to make theneasier to handle duringconstruction, and thencut them down beforeputting them inside thecase.


Circuit diagram for tester unit


You have to cut somestrips on board. On theswitch board you cuteight strips in themiddle at the third holein from one side. Onthe LED board, you cuteight strips in themiddle at the secondhold in from one side.The switch board ismounted to the case,so you need to drill ahole at each end to fityour bolts through.

Next we mount the DILsocket and SIL array

on the switchboard. Firstplace the DILsocket so that itstraddles thecut strips, withthe legs of thesocket on thesecond holefrom the edge.

If you bend the legs in slightly when you've pushed it intothe board it'll stop the socket from falling out. Then youmount the SIL array alongside the socket in the first line ofholes. Make sure that the ninth pin of the SIL array with thelarge dot is on the strip in front of the DIL socket – theother eight pins should then line up with the eight legs ofthe DIL socket. Then solder everything to the board (seeabove, middle).

Next we insert the LEDs into the LED board. The reason orusing 3mm LEDs is that they line up better in a smallspace. But the 3mm wide LEDs still have problems onstripboard where the holes are 2.54mm apart.

So, begin by inserting the first and the last LEDs. Makesure that the long leg – the anode – is facing the centre ofthe board, not the edge. Then slide a 6mm wide strip of

card in between the legs (see above). This helps ensurethat the LEDs all line up to the correct height – it alsoensures that there's enough slack in the legs to fit themtrough a small hole in the case. Then inset the six otherLEDs so that they all line up along the card. Finally,because they are spread apart, the LEDs at the edge don'tpoint straight up. So get some point-nosed pliers andtweak them straight (see above right).

Now you cansolder in theLEDs. Problemis, the won'tstand up. So putthen betweenthe jaws of thepoint-nosedpliers and they'llstand upenough tosolder them.

We have to connect the cathodes of the LEDs together tcouple them to the negative of the battery. We could wirethem together – but it's fiddly. So instead just bridge acrossthe tracks of the stripboard as you solder each cathode.Finally, on the last LED, bridge the solder onto the emptytrack. This will become the track that we solder thenegative (black) wire of the battery clip to.

Finally, crop off all the LED legs down to he solder joints,and remove the card (see below – note the bridging of thesolder on the cathodes in the left picture).

Now we have to work on the wire connections. Removethe wires from each of the two 15cm lengths of Ethernetcable – if you split one end, they're loose enough to justpull out. Keep the two set of wires separate because youneed to keep thiscolour coding. Italso helps if youunravel the twistedpairs of wires.

Begin by strippingabout 6mm ofinsulation from



each end of each wire. If the wire isn't solid, but made upof many small wires, you have to twist the wire to make asolid end to push through the holes of the stripboard.

Take one set of wires and begin poking them through theholes by each LED's anode. They must be inserted in aspecific order. With the LEDs facing up, the space for thewires is the bottom of the LED board. The LED to the left isnumber 1, and the one on the right is number 8. Insert thewires in the following order:

LED No. Wire colour LED No. Wire colour1 Orange/white 5 Blue/white2 Solid orange 6 Solid green3 Green/white 7 Solid brown4 Solid blue 8 Brown/white

As you inserteach wire pulltight and thenbend the wirearound the sideof the board.Then carefullysolder the wire,and cut off theexcess down tothe solder joint.Again, you canhold the LEDsin the jaws ofthe pliers tokeep themupright (right).

When this iscomplete we

repeat the same process with the switch board. With theDIL socket facing up, the SIL array is at the top of theboard. The switch to the left is number 1, and the one onthe right is number 8. Insert the wires in the same colourorder as for the LED board.

Finally, solder the black wire of the battery clip to the endof thesolderbridgeon theLEDboard.Thensolderthe redwire of

the battery clip to the end pin of the SIL array on the switchboard – the pin with the big spot above it. That completesthe soldering.

Unit assembly

Difficult work's finished – now we begin to assemble andtest the unit.

To begin,we test thewires tomake sure,before wedo anythingelse, thatthe circuitswork OK.Insert theDIPswitches into the DIL socket, making sure that the 'number1' switch is on the left. Connect a battery to the battery clip.Then make sure that all the DIP switches are set to 'off'.

Using the wiring table above, switch on one of the DIPswitches, starting at one, and make sure that the correctLED lights when you connect the same colour wires fromthe switch board and the LED board. If the correct LEDdoesn't light, or a different one lights, check your wiring.

When the circuit check is complete we install the twoboards on the rear of the network socket (see next page).Begin by placing the boards on the rear of the socket.Make sure that they fit, and if not, trim them slightly. You'llalso have to make sure that the wires can be channelledso that the board can fit neatly against the surface.

From the edge of the face, measure the position of the DIPswitches. Then measure the position of the LEDs. Younow plot these positions on the front of the face. You'll alsohave to measure the position of each LED in order to drillthe hole for it to fit into.

Now you have to drill the hole for each LED. Then drill theholes for each of the fixing bolts on the switch board. Thendrill a hole at each corner of the area where the DIPswitches will fit through the face. Now you have to get afret saw and cut out a square between the four DIP switchholes to give a neat square. You can trim the hole using asharp knife. Fit the switch board into place, and fix thebolts through the face and board to keep it there.

Fitting the LEDs is a little more difficult. They fit in placebecause they are tight in their hole. By experimentation wefound that drilling holes for each LED, and then cutting thisinto a long slot with a sharp knife, gave the best fit. TheLEDs are able to shift and fit into the holes because of the



6mm of space created by the piece of card we used whensoldering.

Next we insert the wires into the connector blocks. To dothis we use a small 'IDC insertion tool'. This has a smallplastic notch to push the wire into the connectors, and apair of flaps in front of it to hold the wire straight whilst youalign with the IDC connector (see below).

We take one of the two blocks to be the 'straight' socket(the lower one in the picture), and one to be the 'crossed'socket. These blocks are colour coded to allow easierinsertion of the wires. This is made a little more complexas some have to options (we used the 'B' option).

Most importantly, the wires of the switch board must beinserted into the straight block, and the wires of the LEDboard must be inserted into the crossed block. We insertinto each block in the following order:

LED Wire colour 'Straight' 'Crossed'1 Orange/white Orange/white Orange/white 2 Solid orange Solid orange Solid orange 3 Green/white Green/white Green/white 4 Solid blue Solid blue Blue/white 5 Blue/white Blue/white Solid blue 6 Solid green Solid green Solid green 7 Solid brown Solid brown Brown/white 8 Brown/white Brown/white Solid brown

Having inserted the wires into the first block, we check thatthey are correctly set on the second block using anEthernet cable that we know to be working properly.Connect the cable between the two sockets. Set all theDIP switches to 'off'. Then, from one to eight, set thatswitch to on. Touch the stripped end of the colour codedwire onto the appropriate IDC connector. If it is correctlywired, the correct LED will light, corresponding to the DIPswitch number (see table for order – see picture below foran example using switch no.1).



If the right LED does not light, try the other connectors tosee if you have a connection problem. If all is correct,insert the wire usingthe IDC insertion tool.Then you can crop thewire to the right lengthusing some wirecutters.

When you finish you can switch all the LEDs on one byone to make sure your circuits don't short and cause otherLEDs to light (see picture top of next page). Then mark thefront panel to say which socket is the 'straight' socket andwhich is the 'crossed' socket – this is important for testingdifferent types of cable (this is outlined later).

Finally, webundle thewires to makethe finalassembly lookneat and tidy.Then screw thefront plate ofthe case to theback box. On

the unit we used, the front place wasn't symmetrical. Thismeant that the battery could be neatly accommodated onone side of the case. So, put the battery on the correctside, close up and tighten the screws. The unit is nowfinished.

Using the unit to test cables

It would be simpler to just test the four wires that theEthernet cable uses for data transfer. But the reason wetest all eight is that we can then check for crossed wiring.

The box below shows the usual wiring order for an RJ-45cable. There are two types of fault that can happen:

� Continuity fault – the crimping process doesn't make agood electrical connection between the wire andconnector.

� Wiring fault – wires are inserted in the wrong order.

Using the DIP switches we can check for both of thesefaults. To begin, the unit is set so that all switches are off –to check that all LEDs are off (below left).

To test the unit set the switches to on and check that allthe LEDs light (above, right). The purpose of this is tocheck that the unit functions correctly. You don't have todo this every time, but if you get an error it's a good idea tocheck that it's not the unit that's faulty. You could also do atest by switching each DIP switch on one at a time to makesure that only the corresponding LED lights.

For a normal 'straight' Ethernet cable, linking a computer toa hub, to test the lines arecorrectly wired and thatthere is a good electricalcircuit we set switches 1,2, 3 and 6 to on. If weinsert a cable, thecorresponding LEDsshould light (see right).

For a 'crossed' Ethernet cable, used to link two computersdirectly without a hub you get exactly the same pattern. It'simportant that to test crossed cables that the 'straight' endis inserted in the 'straight' socket, and the other end mustbe in the 'crossed' socket (see wiring diagram at the end ofthis section to find which is which). If you turn all the DIPswitches off, then switch on DIP switch no.1, LED no.3lights. Switch on no.2, LED no.6 lights. Switch on no.3,LED no.1 lights, and switch on no.6, and LED no.2 lights.Even if you haven't checked the wiring of the sockets, on agood cable the difference between the two sequences willtell you whether you're dealing with a straight or crossedcable.

Finally, for a thorough check that the whole cable works,you should turn off all the DIP switches and turn them allon one at a time. This ensures that the non-data wires arealso good. For straight cables the LED corresponding tothe switch should light. But for crossed cables the orderthe LEDs light is 3, 6, 1, 4, 5, 2, 7 and 8.



Fault finding

The best check of any fault is to switch each DIP switch onand off, one at a time. Depending on whether you have astraight or crossed cable, the LEDs will light in a specificsequence.

When the correct LEDfails to light it is likely thatyou have a badconnection – either thecable didn't crimp onto theconnector properly, or awire in the cable itself isfaulty. In these cases, assuming you've got switches 1, 2,3 and 6 'on' o check the data lines, one (or more) of theLEDs will not light (see right).

In this case, set al switches to 'off'. Then, one at a time,switch them on. A bad connection will show itself as anLED that will not light (see below, left). Of course, as we'veonly 1, 2, 3 and 6 switches on, it is possible that a datawire has been wired to the wrong pin on the RJ-45

connector – so it doesn't light because the line to which itis mis-wired is not switched on. To test this you can justswitch on and off each switch to see which LED lights. Forexample, (below, right) if switch 5 lights LED 6 instead ofLED 6, it's likely that the connector has been mis-wired.

The mis-wiring can also show up when you initially test thecable – because although 4 LEDs light, one of them iswrong (see below, left). To test this switch on and off eachswitch to see which LED lights. For example, (below, right)if switch 6 lights LED 5 instead of switch 5, it's likely thatthe connector has been mis-wired.

Either way, a fault means one thing – you need to cutoff one of the connectors and crimp it on again.

If it's a bad connections, cut off one of the connectors andcrimp a new one on. If after repeating the test there's still aproblem, cut off the other connector and try again. If thereis still a bad connection then it's a cable fault.

If it's a mis-wire, which connector is wrong depends uponwhich way around the connectors are. On straight cablesthis doesn't matter, but on crossed cables it does. Crossedcables must have the straight connector in the straightsocket, and the crossed connector in the crossed socket. Ifthis is the case:� If the switch on the data line you are testing lights a

different LED to that required, then it's the connector inthe crossed socket that's likely to be wrong.

� If the LED on the data line you are testing is lit byanother switch, then it's the connector in the straightsocket that's likely to be wrong.

Either way, do a visual check to see which way theconnectors are wired. When you can identify whichconnector was wrongly wired, cut it off and crimp on a newone. They should, depending upon the type of connector(straight/crossed) look like one of the examples below:


Cable testing – a quick 'how to'

1. If necessary test the unit – switch off all switches to makesure all LEDs are off, insert a good (straight) cable, andthen switch on the switches one at a time to make surecorresponding LED lights.

2. For testing a cable quickly, make sure that only switches 1,2, 3 and 6 are switches on.

3. If in doubt, check that the cable is straight/crossed byholding each connector with the metal contact facing you,and pointing to the right. On straight cables bothconnectors will have the white/orange at the top. Oncrossed cables one will have white/orange (the 'straight'end) and one will have green/white (the 'crossed' end).

4. Insert cable into unit – if you are testing a 'crossed' cablemake sure that the 'straight' plug is in the 'straight' socketand the 'crossed' plug is in the 'crossed' socket.

5. If all's well, LEDs 1, 2, 3and 6 will light and noothers – see right.

6. To check all wires,switch off all switches,and then switch them onin order from 1 to 8. Forstraight cables LEDs 1 to 8 will light in sequence. Forcrossed cables, lights 3, 6, 1, 4, 5, 2, 7 and 8 will light insequence.

7. If you don't get this pattern, the cable has a fault and youneed to consult the 'fault finding' section.


Straight Connector Crossed Connector

Parts List and Project Costs

Component Description Source/costTo buy new from Maplins:

Code Title Cost

RJ-45 socket Double RJ-45 wall socket. Can be found in sales of old networkscrap, or bought new for around £10

DP29G 90Deg UTPO/Let Dbl

£10.99

Back box Any back box/patress will do providedthat it's at least 46mm/1.8” deep

Junk shops or local DIY sales. Can bebought new for £1 to £2

DB40T Sur Patt 46mmSngl

£1.49

8x LEDs(green)

Any matching LEDs – we used lowLEDs to reduce battery drain.

Salvage from old electrical equipment– especially AV equip.

CJ56L 2mA 3mmGreen LED

£1.28(8 @ 16p)

DIP switches 8-way DIP switches, single pole singlethrow

Recover from old computercards/peripherals

QY70M Slimline 8W DILSw

£1.49

3.9k SIL array 8-way SIL resistor. Recover from old computercards/peripherals

N80BC 8Res 9pin Array3.9k

£0.12

16-pin DILsocket

Standard 16-pin IC socket. Computer sales, but you may have tobuy one new

BL19V DIL Socket 16pin

£0.14

PP3 batteryclip

PP3 snap on battery clip Recover from any old portableequipment

HF28F PP3 Clip £0.29

PP3 9V battery Alkaline will do, but we used arechargeable NiCd

You may have an old NiCd, but youcould buy an new alkaline

AR46A Duracell PP31pk

£3.79

Hook up wire Two 15cm lengths of eight core (orequivalent)lightweight wire

Could use telephone wire, but we use30cm of Ethernet cable

CW45Y UTP Cat5 Solid1m

£0.39

Small bolts Two small flat headed M3/3mm dia.bolts, around 2cm long, with nuts

Recover from any old electricalequipment or other hardware

N55AKN19AL

M3x25 P SlotM3 Hex Nut

£0.99£0.99

Stripboard 15 strips x 6 holes and 11 strips x 4holes stripboard/veroboard

Should be able to borrow some fromanyone who plays with electronics

JP47B Stripboard 2939 £2.29

TOTAL Trash-tech: Around £15 (wall socket, back box and a new PP3 battery) New: £24.25

For Maplin ordering details see http://www.maplin.co.uk/ or phone 0870 429 6000. Above cost doesn't include tools like cutters, saws,drills, soldering iron and solder. Note you can buy a ready made cable tester from Maplin for £59.99 (code ZY77J).

The Salvage Server Project has been developed by the Free Range Network to promote the use of redundant IT equipment as a resource for community and grass rootscampaigning organisations. This report has been produced to support the work of the project, and is made freely available to encourage the objectives of the project.

© Copyright 2003, Paul Mobbs/Free Range Network. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU FreeDocumentation License, Version 1.2 or any later version published by the Free Software Foundation; with Invariant Sections being the document title and authoridentification, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is provided at: http://www.fraw.org.uk/_admin/rights.html This document has beenwholly produced using the Gnu/Linux operating system and free software.

The information contained in this work has been obtained from sources that are believed to be reliable. However, We cannot provide any absolute guarantee that theinformation contained herein is wholly correct, or that the manner in which the information is used is correct, and consequently we cannot be responsible for any error,omissions or damages arising from the use of the information in this work. This work has been created on the basis that the Free Range Network is not intending tosupply engineering or any other professional services – the purposes of this briefing are merely illustrative.


manual - ethernet cable tester

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