A cable tester device can be built using electronic diagram below.
Using electronic diagram below can test concomitant eight pairs of cable.
Electronic scheme is simple and consists of a clock generator (N1 ... N3) that control the 4-bit counter IC2. From all eight outputs of IC1, one is logical "0" during a certain period of tact. This signal then reaches trough inverters N5…N12 to clips cable connection. The other end of the cable is connected to the N13 .... N20 gates inputs. Among the outputs of these gates and the appropriate output of IC1 is located LEDs (D1 ... D16).
Odd-numbered LEDs (D1, D3, D5 ...) lights when output is in the state corresponding NAND logical "0" and while the corresponding output of IC1 is in state "1" logic. Even-numbered LEDs (D2, D4, D6 ...) lights only when NAND output is in state "1" logic and the corresponding output of IC1 is in state "0" logic.
If one cable is disrupted, the NAND gate output connected to it remains in state "0" logic, the two LEDs belonging to this output, diode corresponding odd number lights. At a correct binding, LEDs remain off, because when anode and cathode potentials oscillate at the same rate. Short-circuits between the cables are shown as in this case an even number LED anode is 1 and cathode is a "0" LED lights.
As long as no cable is not connected, the odd number LEDs lights.