Wire Loop Alarm
The wire loop alarm circuit operates on a straightforward principle involving a closed-loop of wire that, when interrupted, triggers an alert. The core components of the circuit include a power supply, a resistor, a transistor, a siren (or relay), and the tripwire itself.
The tripwire is strategically placed in a doorway or hallway, creating a closed circuit. When an intruder breaks the wire, the circuit opens, causing a change in current flow. This change is detected by the transistor, which acts as a switch. The transistor is typically configured in a common-emitter configuration, where it amplifies the change in current to drive the siren.
The siren serves as the primary alert mechanism. In the basic configuration, a small siren is connected directly to the output of the transistor. However, for applications requiring a more robust alert system, the siren can be replaced with a relay. This relay can control larger external devices, such as industrial sirens or commercial alarm systems, enhancing the overall effectiveness of the alarm system.
The circuit should also include a resistor in series with the base of the transistor to limit the current flowing into it, ensuring that the transistor operates within safe limits. Additionally, a diode may be placed in parallel with the relay to protect the circuit from back EMF generated when the relay coil is de-energized.
For optimal performance, the power supply voltage must be chosen to match the specifications of the components used, particularly the siren or relay. Common supply voltages for such circuits are typically 9V to 12V, depending on the requirements of the siren or relay.
Overall, this simple wire loop alarm circuit provides an effective and low-cost solution for security applications, offering flexibility in alert mechanisms and ease of installation.This circuit is a simple wire loop alarm that can be used in doorways, hallways, or any other place the tripwire will be broken by intruders. The circuit has a built in siren, but it can be replaced by a relay to drive an external siren, commercial alarm, etc.
🔗 External reference
Related Circuits
The circuit diagram illustrates the three-wire RTD connection for the XTR108. It is important to note that the lead resistance of the RTD sensor can introduce measurement errors. In the provided figure, connections "1" and "2" represent the lead...
This is a simple easy to build transistor based motorcycle alarm. It is designed to work at 12 volts. But if you change the relay for one with a 6-volt coil, it will protect your Classic Bike. The standby...
The ramp voltage from the low-frequency oscillator IC1 modulates IC2, thereby producing a rising and falling tone similar to the wail of police cars. The described circuit utilizes a low-frequency oscillator (IC1) to generate a ramp voltage. This ramp voltage...
This circuit gives out an alarm when its sensor is wetted by water. A 555 astable multivibrator is used here which gives a tone of about 1kHz upon detecting water. The sensor when wetted by water completes the circuit...
A 3-phase power system poses risks to electrical equipment, particularly asynchronous motors. To detect phase failure, an alarm circuit can be implemented. When the power supply is normal, the voltage at point A is approximately 0V, and no alarm...
The tracer detects the weak magnetic field of any current-carrying house wiring and amplifies this signal to a level that is adequate for driving a magnetic earpiece. The unit uses a telephone pick-up coil to detect the magnetic field. The...