El Cheapo Cable Tester

Many cable testers have been published before, some quite complex, but here’s a cheap and simple alternative. It uses only a 9V battery, two mating connecators and a few resistors, as well as a multimeter for voltage measurements. Begin by soldering the leads of a 9V battery clip between the two pins furthest apart on one of the test connectors and then add a ladder of resistors between them for each of the other required pins. Any junk-box resistors will do but values between 1kΩ and 50kΩ are best. In the example shown, a five-core data cable terminated with D-9 connectors is to be tested. Connect 0V to pin 5, +9V to pin 1, and four resistors in between. Plug in a 9V battery and then probe the connector at the other end of the cable with a multimeter as indicated. Broken, shorted or incorrect connections are all quickly evident using this method.

Circuit diagram: