0 How to build An Expandable Multi-Zone Modular Burglar Alarm

Description

The Basic Alarm Circuit has an automatic Exit/Entry Zone - an Instant Alarm Zone that will accept both normally-closed and normally-open triggering devices - and an "Always On" 24-hour Personal Attack/Tamper Zone. By using the Expansion Modules - you can add as many extra alarm zones as you require.

Schematic Diagram

The Alarm is armed and disarmed by SW1. Before you move the switch to the "set" position - all the green LEDs should be lighting. You then have up to about a minute to leave the building. As you do so - the Buzzer will sound. It should stop sounding when you close the door behind you. This indicates that the Exit/Entry loop has been successfully restored within the time allowed. 

When you re-enter the building - you have up to about a minute to move SW1 to the "off" position. If SW1 is not switched off in time - the relay will energize - and the main bell will ring. It will continue ringing for up to about 40 minutes. But it can be turned off at any time by SW1. 

The "Instant" zone has no Entry Delay. The moment one of its normally-open switches is closed - the main bell will ring. Similarly - the moment one of its normally-closed switches is opened - the main bell will ring. If you don't want to use normally-open switches - leave out R8, C8 and Q2 - and fit a link between Led 3 and C7.

The 24 Hour Personal Attack and Tamper protection is provided by the SCR/Thyristor. If one of the switches in the normally-closed loop is opened - current through R11 will trigger the SCR - and the main bell will ring. In this case the bell has no time limit. To reset the PA/Tamper zone - first restore the normally-closed loop - then press SW2 momentarily. This will interrupt the current and reset the SCR.

Two-Zone Expansion Module

The basic circuit will be satisfactory in many situations. However, if you have a large building to protect - it's much easier to find a fault - when the system is divided into zones - and the control panel can "remember" which zone has caused the activation. 

The expansion modules are designed to do this. Although they will work with the existing instant zone - they are intended to replace it. When a zone is triggered - its red LED will light and remain lit - to indicate that the zone has been activated. 

The idea is that - once you've noted the zone in question - you then press the reset button and turn off the LED. The reset button simply turns off the LED. It doesn't reset the zone. The zone resets automatically when the trigger circuit is restored. If you're using more than one expansion module - they can all share a single reset button.

Inertia-Sensor Module

Detail: How to build An Expandable Multi-Zone Modular Burglar Alarm

0 Heat Detector Alarm using UM3561

A very simple heat detector alarm electronic project can be designed using the UM3561 sound generator circuit and some other common electronic parts . This heat detector electronic circuit project uses a complementary pair comprising npn and pnp transistor to detect heat Collector of T1 transistor is connected to the base of the T2 transistor , while the collector of T2 transistor is connected to RL1 relay T3 and T4 transistors connected in darlington configuration are used to amplify the audio signal from the UM3561 ic.

When the temperature close to the T1 transistor is hot , the resistance to the emitter –collector goes low and it starts conducting . In same time T2 transistor conducts , because its base is connected to the collector of T1 transistor and the RL1 relay energized and switches on the siren which produce a fire engine alarm sound. This electronic circuit project must be powered from a 6 volts DC power supply , but the UM3561 IC is powered using a 3 volt zener diode , because the alarm sound require a 3 volts dc power supply. The relay used in this project must be a 6 volt / 100 ohms relay and the speaker must have a 8 ohms load and 1 watt power.

Detail: Heat Detector Alarm using UM3561

0 Infrared Radar System

Chris from PyroElectro.com has a great article about a do-it-yourself radar system build with PIC18F452. It’s a great hobby project although the schematic is very complicated. This project uses three main devices to create the personal radar system. The IR Range sensor gives output, the pic microcontroller processes it and then displays the output on the led array.

  Infrared Radar Circuit Schematic 

The goal of this project is to create a working ir radar system. The system will only be required to measure close proximity at an angle of 90 degrees as seen in the example above. The range of system is roughly 4-30cm, 20-150cm & 1m-5.5m depending upon which sensor you choose to use. [Link]

Detail: Infrared Radar System

0 Simple Siren Circuit

 Simple Siren Circuit Diagram

This circuit will generate siren sound when S1 pressed and increate sound frequency becuase capacitor C1 charged when switch S1 released the frequency will decreated(C1 discharged).

Try to change resistor R3 if you need to change time interval from low to high frequency and vise versa.

Detail: Simple Siren Circuit

0 Two-Zone Burglar Alarm

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. I've used a 12-volt supply in the diagram - but the circuit 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 you'll 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 don't 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 it's 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

circuit from Link

Detail: Two-Zone Burglar Alarm

0 Make a Photodiode Alarm Circuit Diagram

Make a Photodiode Alarm Circuit Diagram. This Photodiode based Alarm can be used to give a warning alarm when someone passes through a protected area. The circuit is kept standby through a laser beam or IR beam focused on to the Photodiode. When the beam path breaks, alarm will be triggered.

The circuit uses a PN Photodiode in the reverse bias mode to detect light intensity. In the presence of Laser / IR rays, the Photodiode conducts and provides base bias to T1. The NPN transistor T1 conducts and takes the reset pin 4 of IC1 to ground potential. IC1 is wired as an Astable oscillator using the components R3, VR1 and C3. The Astable operates only when its resent pin becomes high. When the Laser / IR beam breaks, current thorough the Photodiode ceases and T1 turns off. The collector voltage of T1 then goes high and enables IC1. The output pulses from IC1 drives the speaker and alarm tone will be generated.

Make a Photodiode Alarm Circuit Diagram

IR Transmitter Circuit

A simple IR transmitter circuit is given which uses Continuous IR rays. The transmitter can emit IR rays up to 5 meters if the IR LEDs are enclosed in black tubes. Link

Detail: Make a Photodiode Alarm Circuit Diagram

0 Simple Purpose Alarm Circuit Diagram

Simple Purpose Alarm Circuit Diagram. The alarm may be used for a variety of applications, such as frost monitor, room temperature monitor, and so on. In the quiescent state, the circuit draws a current of only a few microamperes, so that, in theory at least, a 9 V dry battery (PP3, 6AM6, MN1604, 6LR61) should last for up to ten years. Such a tiny current is not possible when ICs are used, and the circuit is therefore a discrete design. Every four seconds a measuring bridge, which actuates a Schmitt trigger, is switched on for 150 ms by a clock generator. In that period of 150 ms, the resistance of an NTC thermistor, R11, is compared with that of a fixed resistor. If the former is less than the latter, the alarm is set off.

When the circuit is switched on, capacitor C1 is not charged and transistors T1–T3 are off. After switch-on, C1 is charged gradually via R1, R7, and R8, until the base voltage of T1 exceeds the threshold bias. Transistor T1 then comes on and causes T2 and T3 to conduct also. Thereupon, C1 is charged via current source T1-T2-D1, until the current from the source becomes smaller than that flowing through R3 and T3 (about 3 µA). This results in T1 switching off, so that, owing to the coupling with C1, the entire circuit is disabled. Capacitor C1 is (almost) fully charged, so that the anode potential of D1 drops well below 0 V. Only when C1 is charged again can a new cycle begin.

 Simple Purpose Alarm Circuit Diagram

It is obvious that the larger part of the current is used for charging C1. Gate IC1a functions as impedance inverter and feedback stage, and regularly switches on measurement bridge R9–R12-C2-P1 briefly. The bridge is terminated in a differential amplifier, which, in spite of the tiny current (and the consequent small transconductance of the transistors) provides a large amplification and, therefore, a high sensitivity. Resistors R13 and R15 provide through a kind of hysteresis a Schmitt trigger input for the differential amplifier, which results in unambiguous and fast measurement results. Capacitor C2 compensates for the capacitive effect of long cables between sensor and circuit and so prevents false alarms.

If the sensor (R11) is built in the same enclosure as the remainder of the circuit (as, for instance, in a room temperature monitor), C2 and R13 may be omitted. In that case,C3 willabsorb any interference signals and so prevent false alarms. To prevent any residual charge in C3 causing a false alarm when the bridge is in equilibrium, the capacitor is discharged rapidly via D2 when this happens. Gates IC1c and IC1d form an oscillator to drive the buzzer (an a.c. type). Owing to the very high impedance of the clock, an epoxy resin (not pertinax) board must be used for building the alarm. For the same reason, C1 should be a type with very low leakage current. If operation of the alarm is required when the resistance of R11 is higher than that of the fixed resistor, reverse the connections of the elements of the bridge and thus effectively the inverting and non-inverting inputs of the differential amplifier.

An NTC thermistor such as R11 has a resistance at –18 °C that is about ten times as high as that at room temperature. It is, therefore, advisable, if not a must, when precise operation is required, to consult the data sheet of the device or take a number of test readings. For the present circuit, the resistance at –18 °C must be 300–400 kΩ. The value of R12 should be the same. Preset P1 provides fine adjustment of the response threshold. Note that although the prototype uses an NTC thermistor, a different kind of sensor may also be used, provided its electrical specification is known and suits the present circuit.

Author: K. Syttkus
Copyright: Elektor Electronics

Detail: Simple Purpose Alarm Circuit Diagram

0 Simple Water Alarm Circuit Schematic

Simple Water Alarm Circuit Schematic .The LM1830 fluid detector IC from National Semiconduc tor is designed to be able to detect the presence of fluids using a probe. This chip requires a relatively high supply voltage and is not the most frugal power consumer. It is also quite specialised so unless you are buying in bulk the one-off price is not cheap. 

An alternative circuit show n her e uses a standard CMOS IC type 74HC14. It has the advantage of operating with a 3 V supply and consumes less than 1 µA when the alarm is not sounding, this makes it ideal for use with batteries. 

Water Alarm Schematic Circuit Diagram

The 74HC14 has six inverters with hysteresis on their input switching thresholds. A capacitor (C1) and a feedback resistor (R1) is all that’s necessary to make an inverter into a square wave signal generator. 

In the water alarm circuit the feedback resistor consists of R1 and the water sensor in series. R1 prevents any possibility of short-circuit between the inverter’s input and out-put. Resistor R2 defines the inverter’s input signal level when the sensor is not in water. Any open-circuit (floating) input can cause the inverter to oscillate and draw more current.The remaining inverters in the package (IC1.B to IC1.F) drive the piezo buzzer to produce an alarm signal. Capacitor C2 ensures that no DC current flows when the circuit is in monitoring mode (with the alarm silent) this helps reduce the supply current. 

A micro-switch can also be substituted for the water sensor to make the circuit a more general purpose alarm generator.

Author: Roland Heimann - Copyright: Elektor

Detail: Simple Water Alarm Circuit Schematic

0 VFD Talking Alarm Clock

Are you having a hard time waking your hubby from sleeping? And when you leave the house for work, are you in doubt that he has not gotten out of bed? One thing that will stop your worries is to use this clock that does not just tell time but also “swears”.

This is an All-in-one alarm clock. It shows an alphanumeric character, it has a calendar, temperature, and a light sensor to control its brightness. You can plug it on to your power source or use a battery. Although this is cool, It’s not ok being around kids. We don’t want young kids to learn to swear or say bad things, right? 

Detail: VFD Talking Alarm Clock

0 Build an IR Beam Breaker Circuit Diagram

IR Beam Breaker Circuit Diagram. This is an Infrared beam breaking alarm ideal to use in entry or passages.It is based on the working of the popular IR sensor Module TSOP 1738 which senses 38 kHz Infrared pulses from the IR LED of the transmitter. Range of the circuit is about 5 meters if the transmitter and receiver are properly aligned

TSOP 1738 IR sensor module responds to only 38kHz pulsed infrared rays. It will not sense continuous IR ray from the IR LED.So a transmitter circuit(as one in TV remote handset) based on 555 IC is required. Any standard transmitter circuit based on 555 IC can be used. But its output should be 38kHz exactly. TSOP 1738 gives 5 volt output and 5mA current in the off position.

 That is when IR rays are not available.Its output is current sinking so that when it receives 38kHz IR rays, output becomes zero.Pin 2 of the module should get a supply voltage between 4.5 to 6 volts.Higher voltage above 6 volts will destroy the device. The module is generally immune to ambient light, but may responds to sources of noice such as electronic ballasts.

IR Beam Breaker Schematics

Out put from the IR module is given to the inverting input of IC1. LM311 is a precision voltage comparator . It looks like the common Op Amps like LM741, CA3130,CA 3140,TL071 etc.But its pin connections and output are different from other Op Amps.

Pin 2 Non inverting
Pin3 Inverting
Pin 1 Ground
Pin8 Vcc
Pin7 Current sinking Output

The non inverting input of IC1 is connected to a potential divider comprising R1 and R2. When the IR sensor gets IR pulses from the transmitter, output of IC1 remains high. When the IR beam breaks, output from the sensor becomes high which triggers IC1. It then sinks current to activate buzzer and LED. link

Detail: Build an IR Beam Breaker Circuit Diagram

0 Automatic Car Alarm Circuit Diagram

Automatic Car Alarm Circuit Diagram. Even the best car alarm is useless if you forget to set it upon leaving your car, whence this circuit. The relay has a make and a break contact: the  former is necessary to delay the switching in of the  alarm after you have got out of your car, and the  latter serves to switch on the car alarm proper. Immediately on re-entering your car, you must press the hidden switch, Si. This causes silicon-controlled rectifier Thi to conduct so that the relay is energized. At the same time, the green LED lights to indicate that the alarm is switched off.  

Automatic Car Alarm Circuit Diagram

 Best Automatic Car Alarm Circuit Diagram

As soon as the ignition is switched off, T, is off, T2  is on, and the buzzer sounds. At the same time,  monostable IC1 is triggered, which causes T3 to  conduct and the red LED to light. The silicon- controlled rectifier is then off, and D4 is reverse  biased, but the relay remains energized via its make  contact for a short time, preset by Pi As soon as this  time has lapsed, the relay returns to its quiescent  state, and the alarm is set via the break contact. The  delay time can be set to a maximum of about 1 minute.

Detail: Automatic Car Alarm Circuit Diagram

0 Emergency Siren Simulator Circuit Diagram

This siren circuit simulates police, fire or other emergency sirens that produce an up and down wail.
 .

Simple Emergency Siren Simulator Circuit Diagram

The heart of the circuit is the two transistor flasher with frequency modulation applied to the base of the first transistor. When the pushbutton is depressed, the frequency of oscillation climbs to a peak and when the button is released, the frequency descends due to the rising and falling voltage on the 22 uF capacitor. The rate of change is determined by the capacitor value and the 100k resistor from the pushbutton.  The oscillation eventually stops if the button is not depressed and the current consumption drops to a tiny level so no power switch is needed.

The 0.1 uF determines the pitch of the siren: A 0.047uF will give a higher pitch siren and a 0.001 uF will give an ultrasonic (at least for me, anyway) siren from 15 to 30 kHz which might have an interesting effect on the neighborhood dogs! The 33k resistor from the collector of the PNP to the base of the NPN widens the pulse to the speaker giving greater volume.

The flasher circuit drives a PNP transistor which powers the speaker. This transistor may be a small-signal transistor like the 2N4403 in most applications since it will not dissipate much power thanks to the rapid on-and-off switching. The 100 ohm and 100uF capacitor in series with the speaker limit the current to about 60 mA and they may be replaced with a short circuit for a louder siren as long as the transistor can take the increased current. The prototype drew about 120 mA when shorted which is fine for the 2N4403.

Transistor substitutions should be fine - try just about any small-signal transistors but avoid high frequency types so that you do not end up with unwanted RF oscillations. link

Detail: Emergency Siren Simulator Circuit Diagram

0 Cheap Bicycle Alarm Schematics Circuit

The author wanted a very cheap and simple alarm for some of his possessions, such as his electrically assisted bicycle. This alarm is based on a cheap window alarm, which has a time-switch added to it with a 1-minute time-out. The output  pulse of the 555 replaces the reed switch in the window alarm. The 555 is triggered by a sensor mounted near the front  wheel, in combination with a magnet that is mounted on the spokes. This sensor and the magnet were taken from a cheap bicycle computer. 

Cheap Bicycle Alarm Schematics Circuit diagram :

Cheap Bicycle Alarm Circuit Diagram

The front wheel of the bicycle is kept unlocked, so that the reed  switch closes momentarily when the wheel turns. This  triggers the 555, which in turn activates the window alarm. The circuit around the 555 takes very little current and can  be powered by the batteries in the window alarm.  There  is just enough room  left inside the enclosure of the window  alarm to mount the time-switch inside it. 

The result is a very cheap, compact device, with only a single cable going to the reed switch on the front wheel. And the noise this thing produces is just unbelievable! After about one minute the noise stops and the alarm goes back into standby mode. The bicycle alarm should be mounted in an inconspicuous place, such as underneath the saddle, inside a (large) front light, in the battery compartment, etc.

Hopefully the alarm scares any potential thief away, or at least it makes other members of the public aware that something isn't quite right. 

Caution. The installation and use of this circuit may be subject to legal restrictions in your country, state or area.

Detail: Cheap Bicycle Alarm Schematics Circuit

0 Water Level Alert Circuit Diagram

Water Level Alert Circuit Diagram. This circuit will emit an intermittent beep (or will flash a LED) when the water contained into a recipient has reached the desired level. It should be mounted on top of the recipient (e.g. a plastic tank) by means of two crocodile clips, acting also as probes. If a deeper sensing level is needed, the clips can be extended by means of two pieces of stiff wire (see pictures).

Circuit operation:

IC1, a 555 CMos timer chip, is wired as an astable multivibrator whose operating frequency is set by C1, R1 and R2, plus the resistance presented by water across the probes. If the resistance across the probes is zero (i.e. probes shorted), the output frequency will be about 3Hz and the sounder will beep (or the LED will flash) about three times per second. As water usually presents a certain amount of resistance, the actual oscillation frequency will be lower: less than one beep/flash per second. As probes will be increasingly immersed in water, the resistance across them will decrease and the oscillation frequency of IC1 will increase.

This means that a rough aural or visual indication of the level reached by water will be available. If a LED is chosen as the alert, C2, D1 and D2 must be added to the circuit in order to double the output voltage, thus allowing proper LED operation (see the rightmost part of the schematics). Interesting features of this circuit are 1.5V supply and ultra-low current consumption: 40µA in stand-by and 0.5mA in operation. This allows a single AAA alkaline cell to last several years and the saving of the power on/off switch.

Pictures of the project:

Screenshoot - Water Level Alert Circuit Schematic

Water Level Alert Circuit Diagram:

Water Level Alert Circuit Diagram

Parts:

R1 = 1K - 1/4W Resistor
R2 = 100K - 1/4W Resistor (See Notes)
C1 = 2.2uF-50V Electrolytic Capacitor
C2 = 220µF - 25V Electrolytic Capacitor (See Notes)
D1 = 5 or 10mm. Ultra-bright red LED (See Notes)
D2 = 1N5819 - 40V 1A Schottky-barrier Diode (See Notes)
IC = 7555 or TS555CN CMos Timer IC
BZ = Piezo sounder (incorporating 3KHz oscillator)
B1 = 1.5V Battery (AAA or AA cell etc.)
Two small crocodile clips
Two pieces of stiff wire of suitable length
Battery socket, etc.

Notes:

• If a LED alert is needed instead of the beeper, R2 value must be changed to 10K, the Piezo sounder can be omitted and D1, D2 and C2 must be added, as shown in the rightmost part of the schematics.
• A common red LED can be used for D1, but ultra-bright types are preferred.
• Any Schottky-barrier type diode can be used in place of the 1N5819, e.g. the BAT46, rated @ 100V 150mA.
• Wipe the probes regularly to avoid excessive resistance variations due to partial oxidization.

Source: Red Free Circuit Design

Detail: Water Level Alert Circuit Diagram

0 Simple Anti Bag Snatching Alarm Circuit Diagram

Simple Anti Bag Snatching Alarm Circuit Diagram. The heart of this entire circuit anti bag snatching alarm is operational amplifier IC CA3140 (IC₁), configured as a comparator. The two inputs (inverting and non – inverting) is given to pin no 3 and 2 of operational amplifier respectively and output is obtained from pin no 6. Here IC₂ (timer IC NE555) is used as monostable multivibrator. The timing component of anti bag snatching alarm is R₅, VR₁, and capacitor C₂ with the given value in this circuit diagram lets the time of timer is about 1 minute.

For audio section, IC₃ is used as alarm tone generator with an inbuilt oscillator. Finally the output is obtained from pin no 3 of IC₃ and amplified by transistor T₁ in order to get desire level and lastly fed to loudspeaker for output.

Simple Anti Bag Snatching Alarm Circuit Diagram

PARTS LIST

Resistors (all ¼-watt, ± 5% Carbon)

R₁, R₂, R₃ = 100 KΩ

R₄, R₆ = 10 KΩ

R₅ = 10 MΩ

R₇ = 330 Ω

R₈ = 220 KΩ

R₉ = 1 KΩ

VR₁ = 10 MΩ

Capacitors

C₁, C₃ = 0.0047 µF

C₂ = 4.7 µF/16V

C₄ = 0.01 µF

Semiconductors

IC₁ = CA3140 (operational amplifier)

IC₂ = NE555 (timer IC)

IC₃ = UM3561 (complex ROM with an inbuilt oscillator)

T₁ = BD139

ZD₁ = 3.3V 500mA

Miscellaneous

SW₁ = ON/OFF switch

L₁ = speaker 8Ω 1W

Mono plug, mono jack 8

Detail: Simple Anti Bag Snatching Alarm Circuit Diagram

0 Build a Beeper visual indicator Circuit Diagram

This entire circuit of beeper cum visual indicator is build and fabricated around two timer ICs and is configured in an astable multivibrator mode. The frequency generated by IC₁ is controlled by capacitor C₁. The output from pin 3 of IC₁ is given to input pin 4 of IC₂ and base of voltage amplifier transistor T₁ through resistor R₄. Flashing light is connected to collector of switching transistor T₂ and grounded through resistor R₇.

The output of IC₂ is obtained from pin 3 and is given to base of power amplifier transistor T₃ used to drive 8-ohm speaker connected to the collector.

NOTE: LED can be replaced with 3V to 12V DC bulb after eliminating resistor R₇.

Beeper visual indicator Circuit Diagram

 

PARTS LIST

Resistors (all ¼-watt, ± 5% Carbon)

R_1, R7 = 330 Ω

R₂ = 6.8 KΩ

R₃ = 5.6 KΩ

R₄ = 47 KΩ

R₅, R₆ = 22 KΩ

Capacitors

C₁ = 100 µF/10V electrolytic

C₂, C₄ = 0.1 µF ceramic disc

C₃ = 0.01 µF ceramic disc

C₅ = 1000 µF/25V electrolytic

Semiconductors

IC₁, IC₂ = NE555 (Timer IC)

T₁ = BC148B

T₂ = SK100

T₃ = SL100B

Miscellaneous

SW₁ = Push-To-On switch

LS₁ = 8-ohm loudspeaker

LED₁ = Flashing LED

Detail: Build a Beeper visual indicator Circuit Diagram

0 Simple Advance Burglar alarm from dual-op amp Circuit

Simple Advance Burglar alarm from dual-op amp Circuit. Device such as burglar alarms and sirens, whose basic purpose is to monitor certain conditions, make enjoyable projects because of the verity of sounds they can generate. Figure 1 shows a simple siren/alarm circuit using a dual-amp MC1458, audio amplifier LM380, and a 1-W speaker. The dual op-amp is used as a signal generator that produces square, pulse and triangular or sawtooth wave froms. The operation of the circuit is as follows. The A1 and A2 op-amps make up a waveform generator in which the output of A1 is a square wave or pulse waveform and that of A2 is either a triangular or sawtooth waveform. 

The potentiometer R2 controls the frequency as well as the type of output waveform of op-amps A1 and A2. The switch SW1 connect the output of A1 or A2 to the audio power amplifier LM380, this in turn drives the speaker. Although not used in the circuit of figure 1, a potentiometer may be connected between (+) and (-) inputs of the power amplifier to control its voltage gain, which in turn controls the sound volume. The sound level produced depends on the position of switch SW1, the wiper setting of potentiometer R2, and the value of capacitor C4. Therefore, sound of varying intensities can be obtained by adjusting SW1, R2, and C4. For higher output power (sound intensities), audio power amplifier may be used in the bridge from. This configuration will also require a higher wattage speaker. 

Simple Advance Burglar alarm from dual-op amp Circuit

PARTS LISTS

Resistors (all ¼-watt, ± 5% Carbon)

R₁, R_­4 = 10 KΩ

R₂ = 20 KΩ potentiometer

R₃ = 39 KΩ

Capacitors

C₁, C₃ =0.1 µF

C₂ = 100 µF

C­₄ = 0.05 µF

Semiconductors

IC₁ = MC1458 dual op-amp

IC₂ = LM380 audio power amplifier

Miscellaneous

8Ω 1-W speaker

SW₁ = Three-position switch

Detail: Simple Advance Burglar alarm from dual-op amp Circuit