This cable tester allows you to quickly check audio cables for broken wires. Because of the low power supply voltage, batteries can be used which makes the circuit portable, and therefore can be used on location.
Cable Tester Circuit diagram:
The design is very simple and well organ-ised: using the rotary switch, you select which conductor in the cable to test. The corresponding LED will light up as indication of the selected conductor. This is also an indication that the power supply volt-age is present. If there is a break in the cable, or a loose connection, a second LED will light up, corresponding to the selected conductor. You can also see immediately if there is an internal short circuit when other than the corresponding LEDs light up as well.
You can also test adapter and splitter cables because of the presence of the different connectors.
Two standard AA- or AAA- batteries are sufficient for the power supply. It is recommended to use good, low-current type LEDs. It is also a good idea not to use the cheapest brand of connectors, otherwise there can be doubt as to the location of the fault. Is it the cable or the connector.
Source: http://www.ecircuitslab.com/2012/06/simple-cable-tester.html
