Various diagram

Descrition

This is a two-zone alarm - with automatic exit, entry and siren cut-off timers. It can be triggered by the usual types of normally-closed input devices - such as magnetic reed contacts - foil tape - PIRs etc. Ive used a 12-volt supply in the diagram - but the schema will work at anything from 9 to 15-volts. All you need do is select a siren, buzzer and relay to suit the voltage you want to use.

Schematic Diagram

When you move Sw1 to the Set position - you have about 30 seconds to leave the building. If you re-enter through the Exit/Entry zone - the buzzer will sound - and youll have about 30 seconds to switch the alarm off. The Instant zone has no entry delay. Anyone entering through the Instant zone - will sound the siren immediately.

About ten minutes after the normally-closed loops have been restored - the siren will switch off - and the alarm will return to standby mode. It can then be re-activated by a subsequent intruder. If you dont want the siren to sound a second time - add the One-Time-Only Module. It forces the siren to switch off after the first ten minutes. And it prevents the alarm from activating a second time. This module has other uses - so its worth a look.

The various timing components are listed in the diagram. If you want to change the length of any of the delays - change the value of the capacitor and/or the resistor shown. Increasing the value of either - will increases the delay. And reducing the value of either - will shorten the delay.

Stripboard Layout

How to build a Simple Sensitive Optical Burglar Alarm Circuit Diagram ? This optical burglar alarm uses two 555 timer ICs. Both the ICs are wired as astable multivibrators. The first astable multivibrator built around IC1 produces low frequencies, while the second astable multivibrator built around IC2 produces audio frequencies.

Simple Sensitive Optical Burglar Alarm Circuit Diagram

General-purpose Darlington photo-transistor 2N5777 (T1) is used as the light sensor. To increase the sensitivity of the schema, npn transistor BC547 (T2) is used.

Place phototransistor T1 where light falls on it continuously. Phototransistor T1 receives light to provide base voltage to transistor T2 . As a result, transistor T2 conducts to keep reset pin 4 of IC1 at low level. This disables the first multivibrator (IC1) and hence the second multivibrator (IC2) also remains reset so the alarm (loudspeaker LS1) does not sound.

When light falling on Darlington phototransistor T1 is obstructed, transistor T2 stops conducting and reset pin 4 of IC1 goes high. This enables the first multivibrator (IC1) and hence also the second multivibrator (IC2). As a result, a beep tone is heard from speaker LS1. The beep rate can be varied by using preset VR1, while the output frequency of IC2 can be varied by using another preset VR2.

The schema works off a simple 6V-12V DC power supply.