Cut Phone Line Detector

A while ago I got an email asking for the schematic of a circuit to detect cut phone lines. It didn’t take me long to find this circuit in Electronics Now. When the circuit detects that a phone line has been cut, it activates a MOSFET which can be used to drive a relay, motor, etc. It can also be connected to a security system. More: 1. The "Load" can be a relay, lamp, motor, etc. The circuit can also be connected to a security system to sound an alarm in case the phone line is cut. 2. If the circuit is connected to a security system or other circuit, both circuits must b

The circuit designed for detecting cut phone lines utilizes a simple yet effective configuration that leverages a MOSFET as the primary switching element. The schematic typically consists of a few key components: a voltage divider, a comparator circuit, a MOSFET, and a load, which may include a relay, lamp, or motor.

When the phone line is intact, the circuit operates normally, allowing a small current to flow through the voltage divider, which keeps the gate of the MOSFET in a low state. This prevents the MOSFET from conducting, and consequently, the load remains off. Upon detecting a cut in the phone line, the voltage at the input to the comparator changes significantly, triggering the MOSFET to turn on. This activation allows current to flow through the load, which can be a relay that closes a circuit to sound an alarm or activate another device.

The load can be connected to various devices, including alarms or indicators, which will alert users of the phone line disruption. Additionally, if integrated into a broader security system, the output from the MOSFET can be used to trigger additional security measures, ensuring comprehensive monitoring and response capabilities.

It is crucial to ensure that the circuit is designed with appropriate ratings for the MOSFET and load components to handle the expected current and voltage levels. Furthermore, if the circuit is connected to a security system, the integration must be carefully planned to avoid interference and ensure reliable operation. This involves proper isolation and signal conditioning to maintain the integrity of both systems.A while ago I got an email asking for the schematic of a circuit to detect cut phone lines. It didn`t take me long to find this circuit in Electronics Now. When the circuit detects that a phone line has been cut, it activates a MOSFET which can be used to drive a relay, motor, etc. It can also be connected to a security system. 1. The "Load" can be a relay, lamp, motor, etc. The circuit can also be connected to a security system to sound an alarm in case the phone line is cut. 2. If the circuit is connected to a security system or other circuit, both circuits must b 🔗 External reference