Bike Guard Alarm Circuit
Posted in Alarm | 2 comments
More projects on: bike
This Simple circuit can be used to Guard your bike from theft. It gives a loud alarm tone if
somebody tries to start the bike. The alarm disables only when the hide switch S2 is opened. The
circuit has little component count and can be easily fixed in the bike.
Working of the circuit is simple. The alarm generator buzzer or Horn is activated by an SCR and
its triggering is under the control of the transistor T1. In the Armed position, Switch S2 is
closed and S1 (Key switch of the bike) is opened. In this state, T1 will not conduct and SCR and
Buzzer remains idle in armed position. When somebody turns on the Key switch of the Bike
using a duplicate key, Capacitor C1 charges through R1, D1 and R2. It will take a time delay of
few minutes to attain full charge in C1. When C1 fully charges T1 conducts and triggers the
SCR. Buzzer connected to the Anode of SCR gets electrical path and it sounds the alarm. LED
also lights to indicate the theft. The time delay is added through C1 so that the alarm will sound
only after the bike is started .This aborts the attempt of theft.
Bike Guard Alarm Circuit diagram
The unit should hide in a place like the Carrier Box. So that switch S2 can be protected. An
additional bike horn can be connected in the place of the buzzer to get loud sound. Connection
point from R1 should go to the key switch point that goes to the engine so that; the unit will be
activated only if the key switch is closed. Time delay can be changed by changing the value of
C1 or R2. Hide switch S2 should be kept closed for arming the bike only after removing the
switch key. Power to the circuit is obtained from the 6/12 volt bike battery. High current type
transistor T1 and SCR are used to handle the high power of bike battery.Use 1 watt resistors to
handle high power.
Note: This circuit is not sufficient if the tricky thief knows some electronics.
About the Author
Name: D. Mohankumar
Total articles written: 197
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Anti-theft Car Alarm circuit
Posted in Alarm | 6 comments
More projects on: automobile
Here is a simple Anti theft car alarm device for your Car. 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 the car after arming with the device
The anti theft alarm circuit taps power supply from the car battery. Switch S1 is the on/ off
switch of the alarm circuit. When the circuit is activated through S1, the flashing LED blinks
indicating that the car is armed. But the alarm generator works only if the Dome lamp of the car
is switched on through the door switch. This switch turns on the dome lamp, if any one of the
door is opened. The user can put S1 in the on position before leaving the car.
There will be a delay of 2 minutes so that the alarm will not be generated. When the intruder
opens the door, Diode D1 forward biases and capacitor C1 charges through R1. It takes around 1
minute to charge C1. When C1 fully charges, the 12 volt Zener conducts to trigger the NPN
transistor T1.Zener diode switch is provided to avoid false triggering and T1 conducts only when
C1 charges fully. When T1 conducts C2 charges and the voltage in C2 triggers the gate of SCR.
The Horn connected to the Anode of the SCR sounds indicating the theft. The horn can be either
a spare car horn or a Hooter that gives loud alarm.
Anti-theft Car Alarm Circuit diagram
Note: Before leaving the car, switch on S1 and after entering the car switch off S1. Hide S1 in a
place that cannot be detected.
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Total articles written: 197
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Simple Touch Alarm circuit
Posted in Alarm | 6 comments
More projects on: touch switch
Touch the sensor of the alarm with your finger and it starts beeping, goes on for some time and
then stops. Touching it again, and it goes again! This little and flexible circuit consists of a touch
sensor and a directly coupled transistor amplifier with a small loudspeaker as the output load.
Two sensor strips of metal are mounted side by side on a 1×1 cm size micasheet and connected
to the input of the circuit.
How the touch alarm works
Under normal conditions no current flows through switching transistors T1 and T2 and the
potential across capacitor C1 is almost 0V. If the two touch plates are touched together by a
finger, the alarm circuit is enabled by T1 and T2. Transistors T3and T4 form a complimentary
pair amplifier, with positive feedback (regeneration) provided to the base of first transistor T3
via R3 and C2.
The sound generator oscillates at a frequency determined by C2 and R3 and the bias voltage of
T3. The bias voltage of T3 can be changed by changing the values of R2 (and R1). The alarm
will provide quite loud audio output into an 8 Ohm speaker with a 9V battery at a current drain
of less than 100mA. Needless to say, this is an ultra simple hobby circuit. You can experiment
with different component values (R1,R2,C1,C2,R3 and R4, etc) to make your own special alarm!
Touch Alarm Circuit Schematic
About the Author
Name: Tridev Kripa
Total articles written: 54
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6 Responses to “Simple Touch Alarm circuit”
1.
Pradeep
February 5, 2011 at 7:36 pm
I tried that circuit.. But i couldn’t got exact output. Without touching those 2 plates i
heared the buzzer sound…!
Reply
2.
T.K.Hareendran
February 6, 2011 at 3:44 am
The sounder is not a buzzer.It is an ordinary Loudspeaker!
Recheck your circuit for any wrong wiring at the front end ie T1,T2 etc.Finally try to
increase the value of R1.This circuit is highly sensitive& even a small bridge between the
touch points ,formed by solder flux in PCB will trigger it.
Reply
3.
ranjan
February 6, 2011 at 4:38 pm
diploma in electronics and communication (2nd year)
Reply
4.
satwinder hundal
April 24, 2011 at 1:35 pm
i’ve made it with a single touch plate
Reply
5.
sarathy
May 12, 2011 at 11:28 am
sir,
can produce me the full detailed explanation of its working .
Reply
6.
twinkle thakur
July 5, 2011 at 12:41 pm
plz send me principle and full details
Sensitive Freezer Alarm with Buzzer
Posted in Alarm | 2 comments
Here is a simple freezer alarm circuit, but ultra sensitive with a buzzer. The circuit raises an
audio alert when the temperature inside the freezer box goes up above a preset level. The circuit
requires 9V dc supply and can power from a standard 9V alkaline battery.
A negative temperature co-efficient type (NTC type) small thermistor (R1) here works as the freezer
status sensor. Related components (T1 and T2) are used to drive a 6 to 9V rated mechanical buzzer.
When the sensor detects a temperature shoot, the buzzer starts beeping and remains in that condition,
till power to the circuit is removed. For this on/off plus reset function any small dc toggle switch can be
inserted at the positive rail.
Freezer Alarm Circuit Schematic
About the Author
Name: Tridev Kripa
Total articles written: 54
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2 Responses to “Sensitive Freezer Alarm with Buzzer”
1.
Navinesh
March 6, 2011 at 12:48 am
Please can you give me the detail specification and the design for this circuit as i am
doing the project on this here in Fiji. Your help and support would be greatly appreciated.
Please provide as much as information possible or if there is any other designed circuit i
would appreciate to receive.
Reply
2.
KULDEEP PATEL
March 7, 2011 at 10:11 am
PLESE HELP ME IN THIS PROJECT
Pressure Sensor Alarm
Posted in Alarm, Measure | 4 comments
More projects on: 555 • sensor
General purpose circuit of the simple pressure sensor alarm is built around a couple of readily
available cheap components. Working of this circuit is straight forward and self-explanatory.
When the circuit is powered by a 9V compact battery, the active piezo-sounder at the output of
IC1 starts beeping for a short time and then goes into idle state.
Whenever, the pressure sensor element (Piezo-ceramic wafer) is gently tapped, mosfet T1 is fired by the
electric pulse from the sensor through related components and IC1 is again enabled by T1. As a result,
the piezo-sounder starts beeping for a short duration, set by the in-circuit values of R3 and C2. Piezosounder at the output of IC1 can be replaced with a low current 6 to 9 V electromagnetic/solid-state
relay to control external loads. Likewise, values of components T1,R3 and C2 are not very critical.
You can experiment with another values to “tune” the circuit as per your requirements. Pressure
sensors (in piezo-wafer form) are widely available with reputed hobby electronics components dealers.
Possible Applications of this pressure sensor circuit:
Automatic Door Bell, Carpet Alarm, Hit Switch, Knock Bell, Garage Alarm, Doormat Sensor…
Pressure Sensor Alarm Circuit Schematic
555 datasheet
About the Author
Name: Tridev Kripa
Total articles written: 54
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4 Responses to “Pressure Sensor Alarm”
1.
Ed
October 12, 2010 at 6:05 pm
am wondering if this cicue could be adapted to operate a triac, then a relay to turn on a
120ACv well pump. If so, how
Reply
o
T.K.Hareendran
October 17, 2010 at 4:00 pm
Use a low-power SCR,like BT169, at the output of IC555 to drive a 6-9V dc
electro-magnetic relay.Next,you can switch a heavy-duty relay through the 1 C/O
contacts of the first relay.
Reply

Ed
October 17, 2010 at 4:46 pm
Thank you, this what I thought, but like so many other things I
THOUGHT and then applied that didn’t work,, thought I would check it
out on this site first before burning more parts with trial.
After I have applied this system,,, would you know of a touch sensitive
“low voltage” circuit to apply to the previous low to high relay circuit’ I
would like this touch circuit to operate by me touching the plumbing
faucet and using me to complete the ground there-by activating the
wellpump.
Door ajar alarm circuit
Posted in Alarm | 0 comments
More projects on: 4011
Ever accidentally left your front door ajar and had a pet escape? Here is a smart solution to this
problem. The circuit is fairly simple but a great example of using a tiny circuit to get the job
done. All you need is a CD4011 IC plus a handful of components.
In this door ajar alarm/beeper circuit, a bar magnet-reed switch combination is used as the door
sensor. When the door is closed, as per mechanical arrangement, the bar magnet near the reed
switch close its switch contacts. Now the beeper circuit built around CD4011 (IC1) is disabled
by the logic low state at its input terminals (pins 1&12).
When door is opened the beeper is enabled by the logic high state and the speaker starts beeping
intermittently at a rate of about 0.5 secs on/0.5 secs off. Frequeny of this gated aural output is
near 450 Hz. After assembling, enclose the circuit including the reed switch, in a plastic
enclosure and mount it on the door frame.
Next fit the bar magnet in the door exactly in alignment with the reed switch so that when door is
closed the bar magnet is at the close vicinity of the reed switch. For powering the circuit, use an
alkaline type 9V compact battery.
Door ajar beeper/alarm circuit schematic
4011 datasheet
About the Author
Name: Tridev Kripa
Total articles written: 54
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Wire Break Sensor Alarm
Posted in Alarm | 9 comments
More projects on: sensor
Circuit of a loop sensor based simple security alarm is described here. The sensor loop is nothing
but a short length of thin enamelled copper wire, which bridges two input points of the electronic
alarm circuit. When the loop is opened the alarm circuit fires an active electric/electronic hooter
to raise an ear-splitting audio alert signal. The circuit requires 12 volt dc supply for proper
working.
When the loop is closed, anode terminal of diode D1 is at ground level and transistor T1 is off. When the
loop opens, capacitor C1 is quickly charged via resistor R1 and diode D1, whereupon mosfet T1 comes
on so that the hooter (BZ1) is switched on. If the loop is closed again, initial condition is maintained by
grounding the anode of D1 and this stops the charging of C1. However, C1 is disharged fairly slowly via
R2, so that T1 is not switched off immediately! This ensures that the alarm remains active for a little
more time and then goes out slowly. This timeout can be changed by varying the value of R1,R2 and C1.
Mosfet T1 may be one of many types of popular n-channel power mosfet, but it should be able to
handle the selected 12V hooter of your choice.
Wire break alarm circuit schematic
About the Author
Name: Tridev Kripa
Total articles written: 54
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9 Responses to “Wire Break Sensor Alarm”
1.
kiran
October 24, 2010 at 7:00 pm
it’s efficient if you provide circuit elements list and it’s applications
Reply
2.
aliasgar poonawala
October 31, 2010 at 6:36 am
sir it will be helpfull if u send me the applications,working principle,etc of this wire break
sensor alarm project so that it will be helpful for me to make the project report,and give
good presentation.please E-mail me the requires as soon as possible on
“ALIASGAR_MIKAIL950@yahoo.com”
i hope u will do the needful.
ALIASGAR
Reply
o
T.K.Hareendran
October 31, 2010 at 12:36 pm
Working principle of this circuit is clearly described in the text portion of the
article.Possible applications include luggage security system for travellers,burglar
alarm unit for home/office protection,etc.
Reply
3.
ankur
January 21, 2011 at 5:00 pm
sir, can u please tell me how can i use trasformer in place of 12 v battery in this circuit
Reply
4.
Selvam
January 21, 2011 at 5:40 pm
Use 12v trf to build a 12v dc powersupply ie battery eliminator.
Reply
5.
arun
February 8, 2011 at 2:53 pm
is get the output
Reply
6.
Rathod Anand M
March 28, 2011 at 9:08 am
Sir, Pls which circuit i used to flow of pressure of water.
Pls how can i used the pressure sensor for the measuring the water pressure.
Please give me reply as soon as possible.
Thank you
Reply
7.
priya kala
March 29, 2011 at 2:16 pm
sir it will be helpfull if u send me the applications,working principle,etc of this wire break
sensor alarm project so that it will be helpful for me to make the project report,and give
good presentation.please E-mail me the requires as soon as possible on
Read more: http://electroschematics.com/6153/wire-break-sensoralarm/#ixzz1HzD1YykV
Reply
8.
soumya
April 1, 2011 at 10:29 am
sir …….can u plz send me the information why r3=100k is used.plz plz do reply sir
Motion Sensor Switch for alarm, light or
water sprinkler
Posted in Alarm, Lights | 10 comments
More projects on: motion sensor • PIR Sensor
The Motion Sensor Switch circuit is a motion sensor controlled automatic water sprinkler but
you can easily add an alarm/light function too. Before beginning the construction contact your
nearest electronics component vendor and procure a readymade box-type Passive Infrared (PIR)
Motion Sensor unit. Such units, packed in a compact enclosure with power input and relay
output terminals are widely available.
In prototype, an unbranded (Made in China) PIR Motion sensor with the following specifications
are used.




Detection Range:10Meter Maximum
Supply Input:12V DC, <500mA
Relay Output :Common(C),Normally Closed(N/C),Normally Opened(N/O)
Relay ON time: 15 Secs (Not Adjustable)
Now install the PIR module hanging from a 3 metre high mast (to cover 10 metre radius area)
and connect its supply and relay terminals to our finished and enclosed circuit, observing right
polarity. A 4-core screened cable can be used for this interconnection. Power the circuit from a
regulated 12VDC adaptor/solar power box.
Whenever the PIR module detect movement of a live body its relay output toggles and the
switching mosfet (T1) in the circuit is switched to on via resistor R1 and related parts. As as
result, the EM relay at the output of T1 is activated and the electric sprinkler gets its supply
through the relay (RLY1) contacts. This contacts (or spare contacts) can also be used to activate
a high-power warning alarm.
Please note that, here T1 is wired as a mini electronic timer. Even after the PIR relay switched
off, output relay (RLY1) remains in on state for a short duration decided by the value of timing
capacitor C2.
Motion Sensor Switch Circuit Schematic
The Electric Sprinkler
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Name: Tridev Kripa
Total articles written: 54
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Motion detector alarm circuit
Posted in Alarm, Measure | 11 comments
More projects on: 555 • HOA1405 • Infrared
This motion detector alarm circuit can detect a moving person from a distance of 1 meter. It uses
a Dual IR Transmitter-Receiver module HOA1405. When the sensor detects the reflected IR
rays, Alarm will sound for 2 minutes. The circuit can be modified for various applications
including AC operated alarm systems.
Motion Detector Circuit Schematic
The main element in the motion detector circuit is the Dual IR reflective sensor HOA 1405. It has a built
in IR diode and an NPN Photo transistor. The black covering of the module filters visible light rays and
allow IR rays to fall on the Photo transistor. When the Photo transistor receives IR rays, it conducts. The
collector of the Photo transistor is connected to the trigger pin2 of a short duration Monostable timer
built around IC NE 555.
With the given values of R4 and C2, output of IC1 remains high for two minutes to light LED
and to activate the buzzer. In the standby state, the photo transistor inside the Dual Reflector
module remains non conducting since its base is not getting IR rays. When a person comes in
front of the module, the reflected IR rays will trigger the Photo transistor and its Collector goes
to ground potential. This triggers the Monostable and Alarm sounds.
IR Dual Reflective Sensors
HOA1405 Datasheet
555 datasheet
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Total articles written: 197
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11 Responses to “Motion detector alarm circuit”
1.
anil kumar lines
March 25, 2010 at 7:55 am
is this movement detecor is using for automatic door opener when a person comes in
front of a door
Reply
2.
D.Mohankumar
March 25, 2010 at 9:15 am
This circuit can be used for automatic door opener with suitable relay operated
mechanical arrangements
Reply
3.
lan
April 25, 2010 at 2:36 pm
can i replace the speaker with lamp 12V
Reply
o
Yong
June 24, 2010 at 7:45 am
posting @lan. I guss that you shold use the TR and RELAY for lamp 12V.
Reply
4.
hana
May 20, 2010 at 6:27 am
i already assemble the circuit properly,why its not working??any advice??
Reply
o
Yong
June 24, 2010 at 7:41 am
Please check the SCHEMATIC of HOA1405 part.
Reply
5.
Simon
May 21, 2010 at 5:06 pm
can we have the calculations of the values on the circuit to see how did the values of
components found? may be we can be able to troubleshoot the fault when the circuit is
not working.
Reply
6.
olufans
July 5, 2010 at 2:57 pm
the working principles of the stages of the motion detector
Reply
7.
JimX
January 31, 2011 at 2:28 pm
i already try the circuit but the alarm keep on ringing when i havent passthrough the
sensor yet but when the alarm stop n i try to pass through the sensor nothing happen?
Any suggestion what wrong with it?
Reply
8.
JimX
January 31, 2011 at 2:42 pm
i already did the circuit but when i havent pass through the sensor yet the alarm already
ringing for a long time but when it stop ring and i try to pass through the sensor nothing
happen. Any idea what happen?
plz reply asap coz my project date almost near….
Reply
9.
ebin
June 22, 2011 at 6:26 pm
sir i want to know about the cost of dual ir reflector
Step Alarm Circuit
Posted in Alarm | 5 comments
More projects on: 555 • L14F1 • Phototransistor
This Circuit can monitor the door steps or Staircase. When a person crosses the steps, the alarm
sounds indicating the entry. The circuit is too sensitive and operates in day light.
The circuit uses an NPN Darlington phototransistor L14F1. It senses the intensity of light through its
exposed base and passes current in the collector- emitter path. When there is light, the phototransistor
conducts and C1 charges up to its full voltage level. The alarm circuit uses a Monostable timer built
around IC NE555. The triggering threshold of IC1 is adjusted using VR1. So normally the trigger pin 2 of
IC1 remains high as set by VR1. When the shadow of the moving person masks the phototransistor, it
turns off allowing C1 to discharge through R1. This momentarily makes the trigger pin 2 of IC1 low and
the timing cycle starts. With the given values of R2 and C2, Buzzer sounds for two minutes.
Step Alarm Circuit
Setting
The circuit can be constructed on a small piece of Perf board. The circuit is designed to operate
in day light. Switch off the circuit in the evening to avoid false alarm. If a lamp is provided
opposite to the phototransistor on the opposite wall of staircase, the circuit can be used as day
and night alarm. Align the lamp in the line – of – sight of Phototransistor. Adjust VR1 till the
circuit becomes silent.
555 datasheet
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Name: D. Mohankumar
Total articles written: 197
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5 Responses to “Step Alarm Circuit”
1.
godsent
September 13, 2010 at 3:47 pm
mahn you are off to a great kind in thinking. . . . . .
could you just help me out in these kinda things. . . . . . .i need your help in my upcoming
projects. . . .myself Godsent from Chennai. . .please reply for my comment. . . . . i need to
talk a lot more about this. . . .
Reply
o
D.Mohankumar
September 15, 2010 at 5:01 am
Thanks for the feedback.Give your mailID
Reply
2.
Ali
October 2, 2010 at 8:11 pm
Isaw your intersting site ,but Ididnot find a clear word about schmatics for security
systms which ar working with magntic tags. thse systems are used in stores as an antithef
system.
At your best regard
Ali
Reply
3.
Vincent
October 31, 2010 at 5:05 pm
Dear sir, is that have another component that can replace the L14F1 phototransistor?
Reply
4.
D.Mohankumar
November 1, 2010 at 4:04 am
Dear Vincent
L14F1 is the darlington NPN transistor with high gain. It has a built in lens in front of it
to focus light into its pn junction .It is too sensitive and highly reliable.Other photo
transistors like 2N 5777 can be used. But sensitivity will be low compared to
L14F1.Keep the base pin of the photo transistor unconnected.
Entry Alarm circuit
Posted in Alarm | 14 comments
More projects on: L14F1 • Phototransistor
This is an Infrared based Brocken beam alarm to protect doors and entry passages. It gives a loud
alarm when somebody crosses the Invisible Infrared barrier. It can protect the doors both day and
night and is free from false triggering. The circuit is too simple and can be a good evening
project for the hobbyists.
The circuit uses Infrared diodes to emit continuous IR rays which are not pulsed as in the case of remote
handsets. The NPN Darlington Photo transistor is used as a light sensor. L14F1 is the ultra sensitive
Darlington photo transistor with high gain. Its collector is connected to the positive rail through VR1 and
the Emitter has a Green LED to indicate standby mode. The base of T1 is left free without connecting
anywhere. This base junction is exposed through the window of T1 so that light photons will bias the
base.
The degree of biasing depends on the intensity of photons.T2 is the alarm driver and its base is
connected to the collector of T1.So that the base bias of T2 depends on the conduction of T1.
When the Infrared rays illuminate the photo transistor, it conducts pulling the base of T1 to
ground level so that it remains off. Red LED and Buzzer connected to the emitter of T2 remains
off in this condition. When a person crosses the IR beam, T1 turns off and its collector voltage
becomes high. T2 then conducts and activates Red LED and buzzer.
L14F1 Datasheet
BC547 Datasheet
Entry Alarm Circuit diagram
The circuit can be constructed on a small piece of Perf board. Assemble R1 and IR LEDs on a
separate board. Fix IR LEDs on one side of the entry and the Phototransistor on the opposite
side. Carefully align IR beam on the Phototransistor so that buzzer will be silent in the standby
mode. Move hand across the beam, buzzer should sound.VR1 adjust the base bias of T2 to keep
the buzzer off in the standby mode.
L14F1 Phototransitor
L14F1 and BC547 Pins
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Name: D. Mohankumar
Total articles written: 197
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14 Responses to “Entry Alarm circuit”
1.
passcod
April 4, 2010 at 2:22 pm
Hi, that’s a great site, which gives plenty of stuff to do in my free time. However, I’m
kind of a newbie in the field, but I’ve got a project that’s ordered by one of my relatives.
It’s a kind of burglar alarm: using a similar mechanism as in this post, when someone
crosses the beam, it sends a VHF (or, if more simple, FM) signal to be received by a
commercial-made radio at home, 250 meters away. There must be no sound or light
emitted locally, only at home, it should be something like a siren/buzzer sound lasting for
around 30seconds. The whole thing must be battery powered.
I was wondering if you could show how to do that; right now I’m looking at joining up
several of your circuits together, but if you could advise on what to do… maybe post
about it…
It would be very much appreciated. Thanks,
–passcod
Reply
2.
D.Mohankumar
April 4, 2010 at 3:06 pm
Thanks for the feed back.I will post a circuit that transmits the
alarm tone in the FM band when the IR bream breaks
Reply
3.
prasad
May 4, 2010 at 8:39 pm
hi i am student of electronics i m in need of one alarm project .
i am need of that alarm circuit diagram whoes circuit will work means buzzer when it is
in light and stop when it is in shadow…..
i have try many web side but that alarms only buzzer when that got shadow…….plz can
you help me????
Reply
4.
nouman nayyer
July 14, 2010 at 1:11 pm
dear sir
sir i made this
but it is not working
it is working opposite
plz help me to improve it
thanks
Reply
5.
D.Mohankumar
July 14, 2010 at 8:17 pm
I think IR LED is not working or distance is more. Keep the photo transistor in a black
tube so that ambient light will not affect its working
Reply
6.
nouman nayyer
July 15, 2010 at 10:50 am
dear sir
first of all thanks alot for giving me your precious time for relying me.
sir i did the same
but buzzer voice becomes low and green led is also lit but buzzer and red led is also
emitting voice and light.
and distance is o more than 2 inches.
Reply
7.
nouman nayyer
July 15, 2010 at 10:51 am
and sir i m using 100R in quarter watt
is this correct???
Reply
8.
D.Mohankumar
July 15, 2010 at 5:09 pm
Adjust VR to set the sensitivity of the phototransistor at the particular light level. If
properly adjusted, base voltage of T2 will be less than 0.6 volt and it will not conduct.If
IK preset is not sufficient, replace it with a 5K preset. Alternately reduce the value of R1
to 10R 1W so that the intensity of IR rays will be more
Reply
9.
nouman nayyer
July 19, 2010 at 6:35 pm
dear sir
sir its not working sir
light and buzzer is still emitting slightly:-(
Reply
10.
D.Mohankumar
July 19, 2010 at 7:31 pm
There is nothing new in the circuit. When IR rays fall on the photo transistor, it conducts
pulling the base of T2 to ground. When the IR beam is broken by the shadow, photo
transistor turns off and its collector becomes high to give base bias to T2 and it conducts
and activates buzzer.Observe the conditions
1. IR rays should focus on the photo transistor
2. Day light should not fall on the photo transistor
3. Use only L14F1 photo transistor
4. Adjust VR to set the base voltage of T2 below 0.6 volts in the standby mode
5. Adjust the distance between IR LED and photo transistor by trial and error
Reply
11.
Bharat
September 9, 2010 at 4:06 pm
Sir, I want to purchase ENTRY ALARM or any other security systems. Please let me
know where can I get this. Please give your Cell No. as well so that I can talk to you.
Thanks.
Bharat
Reply
12.
ravikumar
September 16, 2010 at 3:18 pm
sir iam made one ir circuit but ir led and phototransister position how to connect plz show
me
Reply
13.
jenn
October 20, 2010 at 11:11 am
hi there…let me know if the resistor used is 1watt? or 1/4 watt??
Reply
14.
noxie
May 9, 2011 at 2:22 pm
mr mohankumar i am one of the third year student doing photodiode alarm , and would
like you to help me
Panic Alarm Circuit
Posted in Alarm, DIY | 39 comments
More projects on: 555 • 741 • siren • UM3561
Imagine the Panic situation in the Midnight when an intruder tries to break into the house. This
Alarm will help you with its loud Police siren to abort the attempt of intrusion. With a single
clap, the circuit generates the alarm for three minutes and then goes off. This is sufficient to
catch the attention of neighbours.
The circuit is a sensitive Clap switch with timer action. IC1 is designed as a sensitive inverting amplifier to
amplify the sound signals from the condenser mic. Variable resistor VR1 set the sensitivity of mic and
resistor R1 and VR2 set the gain of the amplifier. If the sensitivity of mic and amplifier is suitably
adjusted, the circuit can detect the sound from a distance of 5meters or more.
Panic Alarm Circuit Diagram
When the mic detects clap sound, the ac signals pass through C1and IC1 amplifies the signal.
This triggers T1 .When T1 conducts, the trigger pin of the Monostable Timer IC2 will be
grounded and the timer triggers. With the given values of R5 and C2, output of IC2 remains high
for three minutes. This high output provides power to the ROM IC UM3561. It generates the
Police Siren since its pin6 remains unconnected. Resistor R8 determines the frequency of
oscillation of IC3.The siren signals are amplified by T2 and the alarm tone can be heard through
the speaker. Zener diode ZD gives 3.1 volt regulated supply to IC3.
UM 3561 Datasheet
555 datasheet
741 IC
About the Author
Name: D. Mohankumar
Total articles written: 197
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39 Responses to “Panic Alarm Circuit”
1.
Ed
June 9, 2010 at 12:33 am
I just can’t tell u how much I have enjoyed this site !! Though I haven’t recieved any
anserws to my questions,,,,yet. I have really looked forward to opening my e-mail to find
NEW and different circuits to build and experiment with. I know zealch about electronics
but find it alluring and fascinating. I have learned,,,even @ 54 yrs of age and I LIKE IT!!
Reply
2.
Arvince
August 11, 2010 at 7:58 pm
Dear sir, i want to use panic alarm for my project. But, here are so hard to find ic um3561
and T2 AC187. what the other component that can be replaced for both component?
please reply this comment. thank
Reply
3.
D.Mohankumar
August 12, 2010 at 5:44 pm
We cannot substitute UM 3561. It is the siren generator IC.A simple buzzer can be
connected at the output of IC555 is UM 3561 is not available. AC 187 can be substituted
with BC547/548 eventhough the sound output will be low.You can use a high gain NPN
transistor for it
Reply
4.
Arvince
August 14, 2010 at 9:18 am
Thank for the information sir.Now, i can proceed my project.
Reply
5.
Arvince
October 11, 2010 at 9:14 am
Dear sir, in my easy pc for panic alarm project, there have no pin ic for um3561, so that i
have to use ic ne555. but,i dont know which pin to connect. can sir please tell me the pin
need to be connected using ic ne555 by refer the ic um3561? thank you,sir
Reply
6.
D.Mohankumar
October 11, 2010 at 7:56 pm
You cannot substitute UM 3561 with 555 IC.Is it a simulation or real building
Reply
o
Arvince
October 12, 2010 at 7:49 am
Dear sir,in my pcb board or real building i use ic um3561, but in the software of
easy pc i am use the pin of ic ne555 because there have no ic um3561 in the
software. i use ic ne555 because just want to connect the pin of the ic.
Reply
7.
Arvince
October 17, 2010 at 10:46 am
Sir, i have problem for the circuit of panic alarm. the speaker has sound but not the alarm
sound. when i take the reading,all the reading show low voltage..microphone also didnt
activated the speaker and zener diode just give 0.55v only even the ic um3561 need 3.1v
to be activated.i dont know what the problem. can sir send me a pcb sketching or other
that are useful to make the panic alarm function?…thank for your kindness..
Reply
o
D.Mohankumar
October 17, 2010 at 6:11 pm
check the output from IC 555. It should be around 10 volts.Red LED will blink
when MIC works. Adjust VR1 for sensitivity.Remove 0.22 capacitor and check
whether IC1 is working. or not.If it is OK, replace a good quality Mic.
Reply
8.
Arvince
October 18, 2010 at 10:26 am
Sir, in the panic alarm circuit, should i add one connection on the pin 5 of ic um3561 to
the positive line or just follow the actual circuit shown?
Reply
o
D.Mohankumar
October 18, 2010 at 4:46 pm
UM 3561 is low power IC with maximum rating of 3 volts. Do not give higher
voltage.IC will burn.
Reply
9.
Arvince
October 18, 2010 at 8:41 pm
Dear sir, i have testing my pcb for panic alarm circuit. Here, i am using the 3.3v led and
when i on the power supply the led reading is 0.6v, the voltage of the microphone is
2.65v..is that the circuit function if the microphone show the voltage 2.65v? thank for the
feedback from sir.
Reply
10.
Arvince
October 19, 2010 at 10:40 am
dear sir,wrong info from me…actually not 3.3v led but the zener diode which is 3.3v..
Reply
11.
Vincent
October 19, 2010 at 2:49 pm
dear sir, my panic alarm in the pcb, when i on the mic the will led on, then the led off
when i off the micro..but, still not give alarm sound to the speaker but just normal
speaker sound out.. the vr1 like to burn when i turn on the power supply.what the
problem that should i fix?
Reply
12.
Vincent
October 24, 2010 at 8:24 am
Dear sir, i have another certain problem for my panic alarm circuit..here didnt sell the
ac187 transistor so i have to use bc548.. when i testing, the speaker give police siren
alarm when i on the supply. the microphone didnt give effect to the circuit. more than
that, the bc548 which i use to replace the ac187 quick hot. what the solution and the
problem for that circuit? thank
Reply
13.
D.Mohankumar
October 24, 2010 at 11:10 am
1. You can use BC 548 instead of AC187. But the output volume will be low.
2. Timer IC 555 is used to give power to UM 3561. So at power on the timer will be
triggered but after the delay time, siren will stop.This helps to know that the Alarm is
working. If the 555 IC is triggering continuously, it is due to the triggering of T1.T1 gets
triggering pulse from IC1.Adjust VR2 to get zero output from IC1 in the standby mode.
3. Check the microphone for continuity. Solder it directly to the PCB with correct
polarity.If you use wire for microphone, sensitivity will be greatly reduced.Adjust VR1 to
get desired sensitivity.If the problem persists, replace 741 IC with CA 3140, more
reliable OP Amp with same pin connection.
4. To check the circuit behind C1, momentarily give 9 volt supply to R1.If the circuit is
working, the problem is with Mic or C1.
5. BC 548 is heating because the load( speaker ) is too high. Use a small 2 inch 8 ohms
speaker.
Reply
14.
Vincent
October 24, 2010 at 7:43 pm
Thank you for your support sir.
Reply
15.
Vincent
October 24, 2010 at 9:49 pm
bc548 : pin no 1 collector, pin no 2 base and pin no 3 emitter
ac187 : pin no 1 emitter, pin no 2 base and pin no 3 collector.
when i use the bc548 to replace the ac187, should i use the pin of bc548 in my pcb or
using ac187 pin in order to connect the circuit in easy pc software according the pin
shown in the above?
Reply
16.
D.Mohankumar
October 25, 2010 at 3:49 am
AC 187 is a high gain NPN transistor with same pin connections as BC 548. Pin 1 is
collector, pin 2 base and pin 3 emitter. The pins are identified from the front side with
number printed.
Reply
17.
Vincent
October 25, 2010 at 12:44 pm
after make correction, when i turn on the power, the alarm at the same time give police
alarm sound.the both variable resistor didnt have effect the circuit. the alarm kept on and
the microphone didnt work.
i dont know what to do
Reply
18.
Vincent
October 29, 2010 at 5:13 pm
Sir, is that ac127 equivalent with ac187?
Reply
19.
Bawek
October 30, 2010 at 8:52 pm
Sir,when i on the power and the same time police siren alarm too active..so, this meant i
have to wait the alarm stop after 3 minutes rite? is that meant when the delay time the ic2
which is ic555 output remain high, the component hot?just want to ensure the part i still
wonder
Reply
20.
D.Mohankumar
October 31, 2010 at 4:46 am
At power on sometimes the Monostable will self trigger. This has one advantage.We can
confirm that the circuit is working. I will post a circuit of monostable without false
triggering.Reduce the current of the power supply to 500 mA or less to avoid heating.
Reply
21.
Bawek
October 31, 2010 at 8:50 am
Dear sir, at power on, the alarm too on.but,the alarm didnt stop on..i am use adaptor as
the power supply.
Reply
22.
Vincent
November 1, 2010 at 6:58 pm
Dear sir,in order to avoid the false triggering,so i have to connect the pin 4 of ic555 with
r1 and c1 rite. I have already put the all component to my pcb board. is that possible if i
use a wire to connect the pin4 of ic555 with r1 and c1?
Reply
23.
Vincent
November 1, 2010 at 7:02 pm
Again, in this panic alarm circuit, how much the the false triggering time?
Reply
24.
Vincent
November 6, 2010 at 8:36 pm
Dear sir, may i know how to improve the condensor microphone?
Reply
25.
D.Mohankumar
November 7, 2010 at 4:16 am
Use a high quality condenser MIC.Adjust VR1 for maximum sensitivity
Reply
26.
Vincent
November 7, 2010 at 3:03 pm
Thank for your kindness sir. Now, my circuit work. Thank for all
Reply
27.
Vincent
November 8, 2010 at 7:35 pm
Dear sir,what is the ac signal meant?
Reply
28.
D.Mohankumar
November 9, 2010 at 3:50 am
Condenser MIC generates AC signals when its diaphragm vibrates due to sound pressure
Reply
29.
Vincent
November 9, 2010 at 7:11 am
Thank for the comment sir.
May i know what dc circuit of power supply suitable for this circuit?
Reply
30.
Vincent
November 10, 2010 at 1:15 pm
Dear sir, is that the mic and the ic ua741 is signal, ne555 receiver and um3561 transmitter
in this panic alarm circuit?
Reply
o
D.Mohankumar
November 10, 2010 at 1:59 pm
Dear Vincent
Mic is the sound sensor. IC 741 amplifies the sound.IC 555 is a monostable timer
to give power to alarm generator IC UM 3561 for short duration
Reply
31.
Vincent
November 10, 2010 at 2:16 pm
Sir, may i know what the block diagram of this panic alarm?
Reply
32.
Bradley
March 9, 2011 at 3:02 pm
Hey, i related very heavily towards this circuit for my AS coursework, however i used an
op amp instead of transistors due to not having the transistors available for me to use.
I also used a 55 to generate a oscillating light to go with the circuit to make the light
trigger aswell as the siren when switched on.
It works extremely well and the only problem i had was a slow time for capacitors
charging before it functioned, however i resolved that.
Thankyou, your circuit was very usefull.
Brad
Reply
33.
sonybagus
March 17, 2011 at 5:05 am
Can I install output speaker with power amplifier 60W ?, I need a loud sound min. 100
dB max. 150 dB. It can make a thief will shock and run. Thanks.
Reply
o
Bradley
April 1, 2011 at 11:26 am
You could install a 60W power amplifier, i have installed a 5W power amplifier
to my circuit and that works to a high enough standard to be heard from atleast
200M away when it is inside a building and switched on, so 60W could be a little
too loud. try a 20-30W power amplifier that should be enough for just a panic
alarm.
Reply
34.
mariam
August 1, 2011 at 11:55 am
sir,may i ask u something about shutter guard project?in the circuit simulation,we can’t
find ic um3561.can i replace that ic with ne555?any suggestion from u sir?thank you for
your reply
Night lamp with alarm
Posted in Alarm, DIY | 1 comment
More projects on: 555 • UM66
This circuit automatically turns on a night lamp when bedroom light is switched off. The lamp
remains ‘on’ until the light sensor senses daylight in the morning. A super-bright white LED is
used as the night lamp. It gives bright and cool light in the room. When the sensor detects the
daylight in the morning, a melodious morning alarm sounds.
The circuit is powered from a standard 0-9V transformer. Diodes D1 through D4 rectify the AC
voltage and the resulting DC voltage is smoothed by C1. Regulator IC 7806 gives regulated 6V
DC to the circuit. A battery backup is provided to power the circuit when mains fails.
When mains supply is available, the 9V rechargeable battery charges via diode D5 and resistor
R1 with a reasonably constant current. In the event of mains failure, the battery automatically
takes up the load without any delay. Diode D5 prevents the battery from discharging backwards
following the mains failure and diode D6 provides current path from the battery.
Night lamp circuit diagram
The circuit utilises light-dependant resistors (LDRs) for sensing darkness and light in the room.
The resistance of LDR is very high in darkness, which reduces to minimum when LDR is fully
illuminated. LDR1 detects darkness, while LDR2 detects light in the morning.
The circuit is designed around the popular timer IC NE555 (IC2), which is configured as a
monostable. IC2 is activated by a low pulse applied to its trigger pin 2. Once triggered, output
pin 3 of IC2 goes high and remains in that position until IC2 is triggered again at its pin 2.
When LDR1 is illuminated with ambient light in the room, its resistance remains low, which
keeps trigger pin 2 of IC2 at a positive potential. As a result, output pin 3 of IC2 goes low and
the white LED remains off. As the illumination of LDR1’s sensitive window reduces, the
resistance of the device increases.
In total darkness, the specified LDR has a resistance in excess of 280 kiloohms. When the
resistance of LDR1 increases, a short pulse is applied to trigger pin 2 of IC2 via resistor R2 (150
kiloohms). This activates the monostable and its output goes high, causing the white LED to
glow.
Low-value capacitor C2 maintains the monostable for continuous operation, eliminating the
timer effect. By increasing the value of C2, the ‘on’ time of the white LED can be adjusted to a
predetermined time.
LDR2 and associated components generate the morning alarm at dawn. LDR2 detects the
ambient light in the room at sunrise and its resistance gradually falls and transistor T1 starts
conducting. When T1 conducts, melody-generator IC UM66 (IC3) gets supply voltage from the
emitter of T1 and it starts producing the melody. The musical tone generated by IC3 is amplified
by single-transistor amplifier T2. Resistor R7 limits the current to IC3 and zener diode ZD limits
the voltage to a safer level of 3.3 volts.
The night lamp circuit can be easily assembled on a general-purpose PCB. Enclose it in a goodquality plastic case with provisions for LDR and LED. Use a reflective holder for white LED to
get a spotlight effect for reading. Place LDRs away from the white LED, preferably on the
backside of the case, to avoid unnecessary illumination. The speaker should be small so as to
make the gadget compact.
UM66 datasheet
555 datasheet
About the Author
Name: P. Marian
Total articles written: 574
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One Response to “Night lamp with alarm”
1.
loganayaki
December 29, 2010 at 2:38 pm
in this is that battery is necessary? without battery can we construct tat?
utomatic Night Lamp with Morning Alarm
Posted in DIY, Lights | 3 comments
More projects on: 555 • UM66
This circuit automatically turns on a night lamp when bedroom light is switched off. The lamp
remains ON until the light sensor senses daylight in the morning. A super-bright white LED is
used as the night lamp. It gives bright and cool light in the room. When the sensor detects the
daylight in the morning, a melodious morning alarm sounds.
The automatic night lamp circuit utilises light-dependant resistors (LDRs) for sensing darkness and light
in the room. The resistance of LDR is very high in darkness, which reduces to minimum when LDR is fully
illuminated. LDR1 detects darkness, while LDR2 detects light in the morning.
Night lamp circuit explanation
When LDR1 is illuminated with ambient light in the room, its resistance remains low, which
keeps trigger pin 2 of IC2 at a positive potential. As a result, output pin 3 of IC2 goes low and
the white LED remains off. As the illumination of LDR1’s sensitive window reduces, the
resistance of the device increases.
In total darkness, the specified LDR has a resistance in excess of 280 kiloohms. When the
resistance of LDR1 increases, a short pulse is applied to trigger pin 2 of IC2 via resistor R2 (150
kiloohms). This activates the monostable and its output goes high, causing the white LED to
glow.
LDR2 and associated components generate the morning alarm at dawn. LDR2 etects the ambient
light in the room at sunrise and its resistance gradually falls and transistor T1 starts conducting.
When T1 conducts, melody-generator IC UM66 (IC3) gets supply voltage from the emitter of T1
and it starts producing the melody. The musical tone generated by IC3 is amplified by single-
transistor amplifier T2. Resistor R7 limits the current to IC3 and zener diode ZD limits the
voltage to a safer level of 3.3 volts.
The night lamp with alarm circuit can be easily assembled on a general-purpose PCB. Enclose it
in a good-quality plastic case with provisions for LDR and LED. Use a reflective holder for
white LED to get a spotlight effect for reading. Place LDRs away from the white LED,
preferably on the backside of the case, to avoid unnecessary illumination. The speaker should be
small so as to make the gadget compact.
Night lamp with alarm circuit diagram
UM66 datasheet
555 datasheet
About the Author
Name: P. Marian
Total articles written: 574
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3 Responses to “Automatic Night Lamp with Morning Alarm”
1.
nilesh
January 7, 2010 at 10:28 am
these are to good for lerning basics of electronics
Reply
2.
s.m
September 21, 2010 at 4:42 pm
what is the use of 4 diodes forming a bridge?can we use IN4007 instead ofIN4001?
Reply
3.
jigar ladhani
January 26, 2011 at 6:43 pm
Its too easy for me to find such extraordinary projects as i am a student.
Smart smoke sensor alarm circuit
Posted in Alarm | 1 comment
More projects on: H21A1
At the heart of this ultra simple smoke sensor or detector alarm is H21A1, which is a photointerrupter module consists of a gallium-arsenide infrared LED coupled to a silicon
phototransistor in a plastic housing. The slot between the infrared sender(LED) and receiver
(phototransistor) allows interruption of the signal with smoke, switching the module output from
‘on’ to ‘off’.
When the smoke enters the slot, the infrared beam falling on the phototransistor is obstructed. As a
result, the phototransistor stops working and the transistors (T1&T2), wired as a simple darlington pair,
conduct to activate the rest of the circuit.
When the darlington pair conducts, the gate voltage of SCR BT169 (T3) goes high and the SCR
is fired. Consequently, the gate terminal of mosfet BS170 (T4) receives positive voltage through
resistor R4 and the active piezo-sounder (BZ1) energises to latch! Visual indicator LED (D1)
lights up instantly. The buzzer sounds to indicate the presence of smoke, unless you switch off
the circuit by disconnecting the 9 volt dc input supply. For optimum performance, adjust
trimpots P1, P2 and the value of resistor R1.
Smoke detector alarm circuit diagram
H21A1 schematic
About the Author
Name: Tridev Kripa
Total articles written: 54
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One Response to “Smart smoke sensor alarm circuit”
1.
sameer
March 17, 2011 at 1:50 pm
its nice sir
Burglar alarm system circuit
Posted in Alarm, DIY | 18 comments
More projects on: 4538 • 555 • Infrared • UM3561
This burglar alarm system circuit is using a infrared proximity detector that triggers an alarm
when the rays falling on its sensor are interrupted. It is different from others burglar alarm
systems because is a very simple diy project and can offer you great satisfaction.
The circuit of IR burglar alarm system comprises transmitter and receiver-cum-alarm sections. It
works off 6V DC, 500mA uninterrupted supply and uses low-cost readily-available electronic
components. LED2 is used for indicating power-on. Check out the infrared alarm circuit too.
Burglar alarm circuit diagram
The transmitted IR signal directly falls on IR sensor TSOP1738. Whenever the IR signal is
interrupted, its output pin 3 goes low and IC2 is triggered at pin 5 through transistor T2. As a
result, its output at pin 7 goes low (for a preset time) to forward bias siren-driver transistor T2.
This condition is indicated by the glowing of LED1. The time-out period can be increased or
decreased by changing the value of capacitor C6.
The output tone of siren-sound generator IC3 can be set by connecting its pin 6 to either Vcc or
GND.
When you connect pin 6 to Vcc IC3 produces the sound of fire-alarm siren, but when you
connect it to GND it produces the sound of ambulance siren.
Burglar alarm assembly
Assemble the transmitter and receiver-cum-alarm circuits on two separate general-purpose PCBs
and house in suitable cabinets. Mount the units on the opposite sides of the entrance gate such
that IR rays from IR LED1 fall directly on the IR receiver module.
555 datasheet
About the Author
Name: P. Marian
Total articles written: 574
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18 Responses to “Burglar alarm system circuit”
1.
raj thanka
August 1, 2009 at 5:10 pm
THIS CIRCUIT IS NOT CLEARLY VISIBLE THIS COMPONENTS VALUES ARE
ALSO CE CANT IDENTIFICATE
Reply
o
sunil baghel
October 14, 2009 at 1:31 pm
if click on the circuit diagram you will see it in LARGE image
Reply

ranga
November 18, 2009 at 2:57 pm
no use clicking the image.. its not getting enlarged.. can u upload another
circuit diagram pls
Reply
2.
raj thanka
August 1, 2009 at 5:12 pm
this circuits are not clearly visible this components are not clearly visible
Reply
3.
shiva sankar sahu
September 4, 2009 at 6:30 am
i am shiva from student of S.M.I.T(ORISSA).i think it is easy project for us……
Reply
4.
Rahul
September 7, 2009 at 6:45 am
Hi,
Its Nice project…….
I like to know how much distance betweem the transmitter and reciever works
properly….
Reply
5.
arun vyas
September 24, 2009 at 4:06 pm
this is the best for new in this fild
Reply
6.
afsal
October 29, 2009 at 10:00 am
i have a better circuit diagram with me ,but it is not working? you try to improve your
circuit
Reply
7.
Simmons
December 12, 2009 at 4:20 am
Has anyone tested this circuit? Is it really working?
Reply
8.
ahsan
July 26, 2010 at 7:41 pm
Its awsum..
Reply
9.
Manthila
August 8, 2010 at 5:28 pm
hello
, has anyone tried this circuit and is it working? Thnkzz
Reply
10.
vik
September 29, 2010 at 1:55 pm
hi, can anyone give me the list of components please as the diagram is unclear. thank you
Reply
11.
rejeesh v r
November 10, 2010 at 10:29 am
can we replace the ic4538 with any other circuit
Reply
12.
sam
January 12, 2011 at 8:10 pm
http://electroschematics.com/wp-content/uploads/2009/04/burglar-alarm-system.jpg
enlarged circuitt diagram
Reply
13.
Om Balsaraf
January 19, 2011 at 9:56 am
The project is really good.
Can you please send me the detailed report along with circuit diagram.
Thanks
Om
Reply
14.
L sandip kumar
April 3, 2011 at 11:28 pm
The project is really good.
Can you please send me the detailed report along with circuit diagram.
Thanks
Reply
15.
sharika A S
April 21, 2011 at 7:16 am
hai,THIS PROJECT IS GOOD AND WE CAN UNDERSTAND SOMANY THINGS
ABOUT THIS CIRCUIT DIAGRAM……. CAN YOU PLEASE SEND THE
DETAILED EXPLANATION ABOUT THIS PROJECT………
Reply
16.
Ahmad
July 30, 2011 at 8:40 pm
do we have to program these ICs ?
Fake Car Alarm Circuit
Posted in Alarm | 2 comments
More projects on: LM3909
This simple fake car alarm or alarm decoy circuit device will simulate the presence of a burglar
alarm in automobiles or homes. It has a few components, uses LM3909 and is easy to build.
Mount R1 where daylight can fall on it. You may change the capacitor value for different
flashing rates.
During darkness, LED1 flashes, making potential intruders think an alarm system is installed.
Fake Car Alarm (Decoy) Circuit Diagram
About the Author
Name: P. Marian
Total articles written: 574
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2 Responses to “Fake Car Alarm Circuit”
1.
Göransson
February 28, 2010 at 7:12 pm
This is a cool circuit, LM3909 has been discontinued, but can still be found. Ordered a
few from Ebay yesterday. Can’t wait till I get a chance to build this circuit!
One question, I assume that the LED’s will be brighter as night falls, not switching on/off
at a certain level, is that right? And if so, is there a way to make it turn on/off without
fade?
Reply
2.
Syed Shiyas
May 11, 2010 at 6:30 pm
Dear Sir,
Me like to construct one security system for my car, Santro GLS model. Can u help?
Thanks in Advance
Shiyas
Emergency Lamp Battery Protector
Posted in Lights | 0 comments
More projects on: 555 • LDR
Emergency lamps do not have a facility to prevent the deep discharge of battery if the lamp
remains on during day time. The fluorescent lamp filament also damages if it is glowing in low
battery voltage. This causes blackening of the filament side that indicates the damaged
filament. So we have to switch off the lamp in the morning and switch it on again in the evening.
By adding this circuit in the emergency lamp you can reduce the job of daily switching. This
circuit offers two advantages
1. It prevents unnecessary discharge of battery during daytime
2. It charges the battery only during night. This saves energy and prevents overcharging of the
battery.
The circuit is a Light controlled switch that connects the Emergency lamp circuit board with
the power supply only during night through a relay. To keep the relay off during daytime, an
LDR and a Schmitt trigger circuit are used. Light Dependent Resistor offers very high
resistance around 10 Meg ohms in dark but in light it has only 100 ohms or less resistance. So it
is an ideal component to switch on circuits based on the presence or absence of sun light. Here it
is used to trigger the timer IC 555 which is designed as a Schmitt trigger.
Schmitt Trigger
The popular Timer IC 555 has two internal comparators. These are Threshold comparator and
Trigger comparator. The Set and Reset action of these comparators can be used for On/ Off
actions. Here the IC 555 functions as a Bistable with Schmitt trigger action. The upper
comparator (Threshold comparator) of IC 555 trips at 2/3 of the supply voltage and the lower
comparator (Trigger comparator) trips at 1/3 of the supply voltage. In the circuit, the inputs (pin6
and pin2) of both the comparators are shorted and connected to the junction of LDR and the
Preset VR.
Emergency Lamp Battery Protector Circuit
In day light, LDR passes more current and the current into the upper comparator (pin6) is above
2/3 Vcc. This resets the internal Flip-Flop of IC. At the same time, the current into the lower
comparator (pin2) is more than 1/3 Vcc. Both these condition causes low output from IC1. This
low output keeps T1 off and the relay also remains off. Battery power supply to the emergency
lamp circuit is connected through the Common and NO (Normally Open) contacts of the relay.
So during daytime the emergency lamp circuits do not get power. The charging process is also
prevented since the connection between the emergency lamp circuit and the battery is broken.
During night, LDR cease to conduct and the Schmitt trigger changes its state and output of IC1
becomes high. This triggers T1 as indicated by the LED. Relay then energizes and the NO
contact makes connection with the Common contact of the relay. This connects the battery with
the emergency lamp circuit.
Assemble the circuit on a Perf board and fix it inside the emergency lamp. Power to the circuit
is obtained from the emergency lamp battery. Cut the positive supply wire of the emergency
lamp circuit that goes to the battery. Solder the cut ends to the common and NO contacts of the
relay. Adjust VR till Relay energize at a particular light level in the evening. Keep LDR on the
back side of the lamp to prevent light falling on it.
LDR resistor
555 IC
About the Author
Name: D. Mohankumar
Total articles written: 197
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Automatic Gate Lamp circuit
Posted in DIY, Lights | 5 comments
More projects on: 555 • LDR
This circuit lights the Premises of House around 6 pm and turns off in the morning. Its working
is fully automatic and uses the light sensing property of LDR. Unlike other LDR based circuits, it
will not cause lamp flickering during the light transition so that CFL and fluorescent lamps can
be used. It also exploits the Schmitt trigger action of timer IC 555 for a clean switching.
LDR and timer IC 555 are used in the circuit for automatic switching. Light Dependent Resistor offers
very high resistance around 10 Meg ohms in dark but in light it has only 100 ohms or less resistance. So
it it is an ideal component to switch on lamps based on the presence or absence of sun light. Here it is
used to trigger the timer IC 555 which is designed as a Schmitt trigger.
Schmitt Trigger
The popular Timer IC 555 has two internal comparators. These are Threshold comparator and
Trigger comparator. The Set and Reset action of these comparators can be used for On/ Off
actions. Here the IC 555 functions as a Bistable with Schmitt trigger action. The upper
comparator (Threshold comparator) of IC 555 trips at 2/3 of the supply voltage and the lower
comparator(Trigger comparator) trips at 1/3 of the supply voltage. In the circuit, the inputs (pin6
and pin2) of both the comparators are shorted and connected to the junction of LDR and the
Preset VR1.
In day light, LDR passes more current and the current into the upper comparator (pin6) is above
2/3 Vcc. This resets the internal Flip-Flop of IC. At the same time, the current into the lower
comparator (pin2) is more than 1/3 Vcc. Both these condition causes low output from IC1.
Automatic Gate Lamp Circuit
When the light falling on the LDR decreases, its resistance increases, and the current flowing to
the upper and lower comparators of IC1 decreases. The input voltage of upper comparator
decreases below 2/3 Vcc and that of lower comparator below 1/3 Vcc. This causes, high output
from pin 3 of IC1. This triggers T1 and the relay connected to its collector turns on. The lamp
gets AC through the Common and NO (Normally Open) contacts of the relay. Only the Phase
line is connected through the relay contacts. The neutral line goes as such.
VR1 adjusts the sensitivity of LDR at the particular light level at which the lamp turns on.
Capacitor C2 maintains the base voltage of T1 for clean switching action and also avoids relay
clicking. Diode D1 removes back e.m.f when T1 switches off.
IC 555 Internal Circuit
Note: LDR should be placed away from the Lamp light but it should get day light. Use 6 Volt
PCB relay. Wiring connections are given in the diagrams.
PCB Relay and Wiring connection
Caution: Take extreme care while connecting AC line to the relay contacts. Do not touch the
relay contacts when the circuit is connected to mains. Provide sleevings to relay contacts to avoid
accidental shorting.
PCB Relay
LDR resistor
555 datasheet
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Name: D. Mohankumar
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