Have you ever wondered if a certain cable was giving your device power from the wall? Here is a way to test the continuity of a cable without touching it directly. The circuit can detect AC signal frequencies, and if the cable is conducting, an LED will light up. The circuit is very sensitive and can pick up signals from the cable's surface, so there's no need to touch the cable directly. Other cables, like modem, audio/video, and dish antenna cables, can be tested with the circuit. Shows how the cable tester works. The op-amp CA3130 is the center of the circuit (IC1). The operational amplifier IC1 has MOSFET inputs and a CMOS output. It has PMOS transistors on the inputs, which give it a very high input impedance and very good speed performance. Even weak signals are easily picked up by the input. The feedback resistors R6 and R7 set the closed-loop voltage gain for IC1, which is wired as a non-inverting amplifier. By adding capacitor C1, a gradual roll-off is made possible. The resistors R1 through R5 are used to set the level of the non-inverting input of IC1. For phase compensation, a capacitor C2 is added between pin 1 (offset null) and pin 8 (strobe). How the circuit works is easy to understand. Bring the circuit's antenna close to the wire you want to test. If the cable is doing its job well, the LED will light up.