5 Zone Alarm System Circuit Diagram

This is a complete alarm system with 5 independent zones suitable for a small office or home environment. It uses just 3 CMOS IC's and features a timed entry / exit zone, 4 immediate zones and a panic button. There are indicators for each zone a "system armed" indicator. The schematic is as follows:

5 Zone Alarm System Circuit Diagram

Circuit Notes

Each zone uses a normally closed contact. These can be micro switches or standard alarm contacts (usually reed switches). Suitable switches can be bought from alarm shops and concealed in door frames, or window ledges.

Zone 1 is a timed zone which must be used as the entry and exit point of the building. Zones 2 - 5 are immediate zones, which will trigger the alarm with no delay. Some RF immunity is provided for long wiring runs by the input capacitors, C1-C5. C7 and R14 also form a transient suppressor. The key switch acts as the Set/Unset and Reset switch. For good security this should be the metal type with a key.

Operation
At switch on, C6 will charge via R11, this acts as the exit delay and is set to around 30 seconds. This can be altered by varying either C6 or R11. Once the timing period has elapsed, LED6 will light, meaning the system is armed. LED6 may be mounted externally (at the bell box for example) and provides visual indication that the system has set. Once set any contact that opens will trigger the alarm, including Zone 1. To prevent triggering the alarm on entry to the building, the concealed re-entry switch must be operated. This will discharge C6 and start the entry timer. The re-entry switch could be a concealed reed switch, located anywhere in a door frame, but invisible to the eye. The panic switch, when pressed, will trigger the alarm when set. Relay contacts RLA1 provide the latch, RLA2 operate the siren or buzzer.

Author : Andy Collinson

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Light Alarms Circuit Diagram

LIGHT ALARM - 1
This circuit operates when lightweight|the sunshine} Dependent Resistor receives light. When no lightweight falls on the LDR, its resistance is high and also the transistor driving the speaker isn't turned on. When lightweight falls on the LDR its resistance decreases and also the collector of the second transistor falls. This turns off the primary transistor slightly via the second 100n and also the initial 100n puts a further spike into the bottom of the second transistor. This continues till the second transistor is turned on as onerous because it will go. the primary 100n is currently nearly charged and it cannot keep the second transistor turned on. The second transistor starts to turn off and each transistors swap conditions to provide the second half of the cycle.

LIGHT ALARM - 2

This circuit is comparable to lightweight Alarm -1 however produces a louder output as a result of the speaker being connected directly to the circuit. The circuit is essentially a high-gain amplifier that's turned on initially by the LDR and then the 10n keeps the circuit turning on till it will activate no more. The circuit then starts to show off and eventually turns off utterly. the present through the LDR starts the cycle once more.

LIGHT ALARM - 3 (MOVEMENT DETECTOR)

This circuit is extremely sensitive and may be placed in a very space to detect the movement of a person up to a pair of metres from the unit.

The circuit is essentially a high-gain amplifier (made of the primary 3 transistors) that is turned on by the LDR or photo Darlington transistor. The third transistor charges the 100u via a diode and this delivers turn-on voltage for the oscillator. The LDR has equal sensitivity to the photo transistor during this circuit.

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24V DC Powered Beeper with 4 Separate Inputs

24v DC is a very popular voltage used in industrial settings. This hobby circuit below was designed to accept four different 24v DC alarm input signals, which are then used to drive a single low power beeper. The beeper is a magnetic type with its own oscillator/driver. The four diodes form an “OR” gate so any one of the four inputs will cause the beeper to make noise. A CMOS version of the popular 555 timer is used to strobe the beeper on and off at about 1Hz.

24V DC Powered Beeper with 4 Separate Inputs Circuit Diagram

 

Copyright: Discover Circuits

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Doorbell Warning Switch Circuit Diagram

This circuit will light a lamp at a remote location when the doorbell switch is pressed. This circuit should only be used with the solenoid type doorbells, the electronic type that play tunes will not work here.  It is quite easy to miss the sound of a doorbell if you are watching TV , this circuit gets round the problem by providing a visual indication. As an alternative, a LED could also be used. You could just parallel a lamp across the doorbell, but this would mean extra drain from the doorbell batteries or transformer.

 Doorbell Warning Switch Circuit Diagram


A series resistor, R1 is wired in series with the doorbell and reduces current flow, thereby increasing battery life. The value of R1 is chosen so that about 0.6 to 0.7 volts is developed across it, when the doorbell switch is pressed. I used a combination of a 22 ohm resistor in parallel with a 50 ohm. The voltage drop across R1 is sufficient to switch on the transistor, the lamp in series with the collector will then illuminate. I also used an electromechanical counter in parallel with the lamp.

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Cash Box Guard Circuit Diagram

Most thefts happen after midnight when people enter the second phase of sleep called 'paradoxical sleep.' Here is a smart security circuit for your cash box that thwarts the theft attempt by activating an emergency beeper. The circuit can also be used to trigger any external burglar alarm unit. The cash box guard circuit (shown in Fig. 1) is built around IC CD4060 (IC1), which has an inbuilt oscillator and divider. The basic oscillator is configured by a simple resistor-capacitor (R-C) network. IC CD4060 divides this oscillator frequency into binary divisions, which are available as outputs.

In light, reset pin 12 of IC1 remains low, which enables the oscillator built around IC1. However, in the dark, it making all the outputs low. This also stops oscillations of the internal oscillator. Working of the circuit is simple. If the cash box is closed, the interior will be dark. Hence in the dark, the light-dependant resistor (LDR1) resets IC1 and it stops oscillating and counting. At the same time, pins 13 and 14 of IC1 go low. So neither the piezobuzzer (PZ1) sounds, nor the relay (RL1) energises, indicating that the cash box is closed.
.

Fig. 1: Cash box guard circuit

If someone tries to open the door of the cash box, light-most probably from the burglar's pen torch -falls on LDR1 fitted into the cash box. As a result, LDR1 conducts and pin 12 of IC1 goes low. IC1 starts oscillating and counting. With the present timing R-C components (at pins 9, 10 and 11), the output timing at pin 14 of IC1 is two-three seconds. Hence pin 14 of IC1 goes high for two seconds after the door is opened and goes low for another two seconds. So the piezobuzzer (PZ1) sounds for two seconds and then falls silent for the following two seconds. This cycle repeats until the cash box is closed.

An optional relay is added for a remotely located audio/visual alert system. For that, a relay driver circuit built around npn transistor BC548 (T2) is used. The relay is energised by the output from pin 13 of IC1 for about four seconds after the door is opened and then de-energised for the following four seconds. You can use this relay to activate another remotely located audio/visual alert system. After assembling the circuit on a small PCB, house it in a small tamper-proof box (refer Fig. 2) leaving a little window for LDR1 and a small opening for the piezobuzzer (PZ1). Now fit the unit inside the cash box (refer Fig. 3) with LDR1 pointing towards the door of the cash box.

Fig. 2: Assemble unit

Note:

1. The relay latching facility can be added to the circuit by replacing transistor T2 with a suitable silicon-controlled rectifier such as BT169.
2. By changing the value of resistor R1, you can adjust the light detection sensitivity of the circuit.
3. If you want to use a 3-pin piezobuzzer device, remove buzzer-driver npn transistor T1 and connect trigger pin of the buzzer directly to pin 14 of IC1. Also connect the positive and negative terminals of the buzzer to respective positive and negative points of the circuit.
4. Photo-transistor 2N5777 can be used in place of the 10mm LDR1.

Fig. 3: Unit fitted inside the cash box & also connected to an external alarm

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ANTI-THEFT ALARM AND HORN

Here is a simple ANTI-THEFT ALARM AND HORN. It generates a loud alarm when there is an attempt of theft. When the intruder opens the door, the circuit senses the attempt of theft and after 2 minutes, the alarm will be activated. The time delay is provided to help the user to leave after arming with the device. 

 ANTI-THEFT ALARM AND HORN Circuit Diagram

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Signal Tracer Circuit Diagram

The main part of this circuit is the LM386 amplifier chip. It also uses a transistor input to buffer the input signal and provide extra gain for the LM386. The little unit has helped me out on numerous occasions when trouble shooting any amplifier circuit like a stereo receiver, tv / vcr audio section, radios, cd players and car stereos.

Circuit Diagram

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A Doorbell for the Deaf Circuit Diagram

This circuit provides a delayed visual indication when a door bell switch is pressed. In addition, a DPDT switch can be moved from within the house which will light a lamp in the door bell switch. The lamp can illuminate the words "Please Wait" for anyone with walking difficulties.


A Doorbell for the Deaf Circuit Diagram :


Notes :
The circuit uses standard 2 wire doorbell cable or loudspeaker wire. In parallel with the doorbell switch, S1, is a 1N4001 diode and a 12 volt 60mA bulb. The bulb is optional, it may be useful for anyone who is slow to answer the door, all you need to do is flick a switch inside the house, and the bulb will illuminate a label saying Please Wait inside the doorbell switch or close to it. The double pole double throw switch sends the doorbell supply to the lamp, the 22 ohm resistor is there to reduce current flow, should the doorbell switch, S1 be pressed while the lamp is on. The resistor needs to be rated 10 watts, the 0.5 Amp fuse protects against short circuits.

When S2 is in the up position (shown as brown contacts), this will illuminate the remote doorbell lamp. When down, (blue contacts) this is the normal position and will illuminate the lamp inside the house. Switch S1 will then charge the 47u capacitor and operate the transistor which lights the lamp. As a door bell switch is only pressed momentarily, then the charge on the capacitor decays slowly, resulting in the lamp being left on for several seconds. If a longer period is needed then the capacitor may be increased in value.

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Emergency Light Alarm Circuit Diagram

Warning! The circuit is connected to 220Vac mains, then some parts in the circuit board are subjected to lethal potential!. Avoid touching the circuit when plugged and enclose it in a plastic box.

Powered by two AA NI-CD batteries Four switchable options

Circuit diagram

 

 

 

Parts:

• R1 220K 1/4W Resistor
• R2 470R 1/2W Resistor
• R3 390R 1/4W Resistor
• R4 1K5 1/4W Resistor
• R5 1R 1/4W Resistor
• R6 10K 1/4W Resistor
• R7 330K 1/4W Resistor
• R8 470R 1/4W Resistor
• R9 100R 1/4W Resistor
• C1 330nF 400V Polyester Capacitor
• C2 10µF 63V Electrolytic Capacitor
• C3 100nF 63V Polyester Capacitor
• C4 10nF 63V Polyester Capacitor
• D1-D5 1N4007 1000V 1A Diodes
• D6 LED Green (any shape)
• D7 1N4148 75V 150mA Diode
• Q1,Q3,Q4 BC547 45V 100mA NPN Transistors
• Q2,Q5 BC327 45V 800mA PNP Transistors
• SW1,SW2 SPST Switches
• SW3 SPDT Switch
• LP1 2.2V or 2.5V 250-300mA Torch Lamp
• SPKR 8 Ohm Loudspeaker
• B1 2.5V Battery (two AA NI-CD rechargeable cells wired in series)
• PL1 Male Mains plug

Device purpose:

This circuit is permanently plugged into a mains socket and NI-CD batteries are trickle-charged. When a power outage occurs, the lamp automatically illuminates. Instead of illuminating a lamp, an alarm sounder can be chosen. When power supply is restored, the lamp or the alarm is switched-off. A switch provides a "latch-up" function, in order to extend lamp or alarm operation even when power is restored.

Circuit operation:

Mains voltage is reduced to about 12V DC at C2's terminals, by means of the reactance of C1 and the diode bridge (D1-D4). Thus avoids the use of a mains transformer. Trickle-charging current for the battery B1 is provided by the series resistor R3, D5 and the green LED D6 that also monitors the presence of mains supply and correct battery charging. Q2 & Q3 form a self-latching pair that start operating when a power outage occurs. In this case, Q1 biasing becomes positive, so this transistor turns on the self latching pair. If SW3 is set as shown in the circuit diagram, the lamp illuminates via SW2, which is normally closed; if set the other way, a square wave audio frequency generator formed by Q4, Q5 and related components is activated, driving the loudspeaker. If SW1 is left open, when mains supply is restored the lamp or the alarm continue to operate. They can be disabled by opening the main on-off switch SW2. If SW1 is closed, restoration of the mains supply terminates lamp or alarm operation, by applying a positive bias to the Base of Q2.

Notes:

Close SW2 after the circuit is plugged.
This circuit was awarded with publication in ELECTRONICS WORLD "Circuit Ideas", September 2001 issue, page 708.

author: RED Free Circuit Designs

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Personal Alarm Circuit Diagram

Small, portable, anti-bag-snatching unit
Also suitable for doors and windows control

Circuit diagram

Parts:

• R1 330K 1/4W Resistor
• R2 100R 1/4W Resistor
• C1 10nF 63V Polyester or Ceramic Capacitor
• C2 100µF 25V Electrolytic Capacitor
• Q1 BC547 45V 100mA NPN Transistor
• Q2 BC327 45V 800mA PNP Transistor
• SW1 Reed Switch and small magnet (See Notes)
• SPKR 8 Ohm Loudspeaker (See Notes)
• B1 3V Battery (two A or AA cells wired in series etc.)

Device purpose:

This circuit, enclosed in a small plastic box, can be placed into a bag or handbag. A small magnet is placed close to the reed switch and connected to the hand or the clothes of the person carrying the bag by means of a tiny cord. If the bag is snatched abruptly, the magnet looses its contact with the reed switch, SW1 opens, the circuit starts oscillating and the loudspeaker emits a loud alarm sound. The device can be reverse connected, i.e. the box can be placed in a pocket and the cord connected to the bag. This device can be very useful in signalling the opening of a door or window: place the box on the frame and the magnet on the movable part in a way that magnet and reed switch are very close when the door or window is closed.

Circuit operation:

A complementary transistor-pair is wired as a high efficiency oscillator, directly driving a small loudspeaker. Low part-count and 3V battery supply enable a very compact construction.

Notes:

• The loudspeaker can be any type, its dimensions are limited only by the box that will contain it.
• An on-off switch is unnecessary because the stand-by current drawing is less than 20µA.
• Current consumption when the alarm is sounding is about 100mA.
• If the circuit is used as anti-bag-snatching, SW1 can be replaced by a 3.5mm mono Jack socket and the magnet by a 3.5mm. mono Jack plug with its internal leads shorted. The Jack plug will be connected with the tiny cord etc.
• Do not supply this circuit with voltages exceeding 4.5V: it will not work and Q2 could be damaged. In any case a 3V supply is the best compromise.Link

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Safety Guard Circuit Diagram

Safety Guard Circuit Diagram. Protect your home appliances from voltage spikes with this simple time delay circuit. Whenever power to the appliances is switched on or resumes after mains failure, the oscillator starts oscillating and D5 blinks. This continues for three minutes. After that, Q14 output of IC CD4060 goes high to trigger the gate of the SCR through D4. At this moment, the voltage is available at the cathode of the SCR, which energizes the relay coil to activate the appliance and D6 glows. Switch SW1 is used for quick start without waiting for delay.

Safety Guard Circuit Diagram:

  

Parts:

R1 = 1M
R2 = 470R
R3 = 820R
R4 = 56K
R5 = 470R
R6 = 1K
R7 = 10K
C1 = 1kuF-25V
C2 = 100nF-63V
C3 = 0.02uF-63V
C4 = 10uF-25V
C5 = 10uF-25V
D1 = 1N4007
D2 = 1N4007
D3 = 1N4007
D4 = 1N4148
D5 = Red LEDs
D6 = Red LEDs
RL1 = 12V Relay
IC1 = AN7809
IC2 = CD4060
SW1 = Switch
T1 = 24V-AC Centre Tapped Transformer

Circuit Operation:

At the heart of the circuit is IC CD4060, which consists of two inverter gates for clock generation and a 14-bit binary ripple counter. Here the clock oscillations are governed by resistor R1 and capacitor C1. In this circuit, only two outputs of the IC (Q5 and Q14) have been used. Q5 is connected to an LED (D5) and Q14 is used to trigger the gate of the SCR through D4 as well as reset the counter. The anode of the SCR is connected to +9V and the cathode is connected to the relay coil. The other pin of the relay coil is connected to the negative supply, while its contacts are used for switching on the appliances.

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Burglar Alarm from dual-op amp Circuit Diagram

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

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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. {Link}

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

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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

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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

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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.

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Emergency Siren Simulator Circuit Diagram

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


 .

 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

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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.

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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? 

Sourced By: Streampowers

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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

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