Recently, I have been building a number of accessories for my base radio, an IC-706 Mk II G. This radio uses an RJ-45 type connector for a microphone connector as do a number of rigs these days. Any mic accessory has to use a similar connector in it's design. Luckily, LAN networks also use this same connector and the parts are even available at places like Home Depot and Lowes.

            When building various devices for the IC-706 series of radios that connect to the microphone connector, wiring the connectors correctly is imperative. Checking the wiring pin to pin can be difficult with the RJ-45 connector because the pins are very small and very close together. What to do? Wiring testers for CAT-5 cable are available at a cost of about 40 to 60 dollars from electronics houses and computer stores. I looked at these and decided that I could build something simpler to suit my needs for about 20 dollars or less, depending on how fully equipped my junk box was.

            The basic information needed when testing a multi-conductor cable like CAT-5 is that each wire in the 4 pair cable goes to the correct pin in the RJ-45 plug and that all crimps are solid. The easiest way to test this is to apply a small voltage to one end of the cable or device and make sure that it comes out on the correct pin at the other end.

            To accomplish this, I built a simple circuit with a RJ-45 female receptacle at either end and to one receptacle I wired a rotary switch to the 8 pins of the jack and the positive end of a pair of AA cells in series to the input pole of the switch. On the other RJ-45 jack I wired the anodes of 8 LED's to the pins of the receptacle and wired the cathodes to a bus leading back to the other contact on the battery holder. No other electronic components are needed, since the LED's will tolerate the 3 volts available without any voltage-dropping resistors needed.

            The switch that I used had 12 possible positions so I left the first one unconnected as an OFF position, wired the next eight positions for lines 1 through 8 and left the last 3 with no connection. The OFF position is really not required since the absence of a cable or device under test effectively makes the circuit open anyway. I just like my toys to have an OFF switch. Battery life with this device is likely to be measured in months or years since the current draw of one LED at a time, and then only when actually testing, will be so minimal as to approach shelf life rating for the batteries.

            The cable or device to be tested is plugged into the two RJ-45 jacks and the rotary switch is turned to each of 8 positions thereby applying 3 volts to each LED in turn through the cable or device being tested. If all is well, each LED will light in turn as the switch is moved to that line. If the wiring is incorrect then the switch will light the wrong LED. If the connections are bad, the LED will not light.

            This simple little gadget makes checking an unknown cable easy and verifying the wiring on a project a snap. Keep on building!