This opto-sensitive circuit sounds an alarm whenever a shadow falls on it. So it can be used at night by shopkeepers to protect the valuables in their showrooms. A dim lighting in the room is necessary to detect the moving shadow. Unlike opto-interruption alarms based on light-dependent resistors (LDRs), it does not require an aligned light beam to illuminate the photo-sensor.
The circuit is powered by a 9V PP3 battery and uses the most sensitive photo-sensor L14F1 to detect shadows.It is portable and can be used at any place that is to be monitored. Op-amp μA741 (IC1) is used as a voltage comparator. Its inverting inputis biased by the voltage obtained from the junction of 100k resistor R1 and the collector of phototransistor T1. The non-inverting input of IC1 gets a controlled voltage from potential divider R2 and VR1.
In the presence of ambient light, the photo transistor conducts and the inverting input (pin 2) of IC1 gets a lower voltage than its non-inverting input (pin 3). This makes the output of IC1 high, which is indicated by the glowing of LED1. When a shadow falls on the photosensor, the output of IC1 goes low. This low pulse triggers the monostable (IC2) designed for a delay of 51 seconds using R6 and C3. The output of IC2 is used to light up LED2 and activate the alarm.
Slide switch S2 is used to select either the buzzer or siren. When it is towards left the buzzer beeps, and when it is towards right IC UM3561 (IC3) activates to give a loud alarm simulating a police siren. Resistor R8 and zener diode ZD1 provide 3.1V DC to IC UM3561. The circuit is easy to assemble as it requires only a few low-cost components. Enclose it in a cabinet with the photo-sensor inside. Drill a 5mm hole on the front panel of the cabinet to let ambient light fall on the photosensor. Adjust potmeter VR1 (47k) until LED2 stops glowing and the buzzer stops beeping while LED1 glows. This is the position of VR1 to be maintained for that particular intensity of light. LED1 will continue to glow even when a shadow is detected.
The circuit is now ready to use. To test it, move a paper in front of the unit. If LED2 glows along with the beep of the buzzer, it means that the photo-sensor has detected a shadow.
Post Comment
Im not geting output for this project.... what can i doplz reply fast
I GOT OUTPUT .THERE MIGHT BE ANY LOOSE CONNECTIONS.CHECK IT.
can we use transformer in place of 9v battery?
yes u can use I have used a 12v step down transformer and got 9v regulated supply using ic-7809.
its good project
it will have disadvantages?
will it work if I replace the alam with a fan and how can I change DC to AC?plz send me the circut diagram too.
if they switch off that dim light????????????????????
I implemented this circuit on a bread board.I used L14G3 instead of L14F1a 9v regualted power supply from a 12v step down transformer and rest same as in the given circuit.I got the following problem1.Both Leds are glowing.2.Buzzer continuously beeping even though I am changing the potentiometer volume.And one thing I want to ask is that whether the wire joining pin 6 of uA741 and pin 2 of ne555 is shorted with 10k and 100 ohm joining wire or not?I EXPECT A FRUITFUL ANSWER AS SOON AS POSSIBLE FROM UR WEBSITE OTHERWISE THERE IS NO USE OF ME AND THOUSANDS OTHERS REGISTERING IN UR WEBSITE
You can use L14G3 and any other 9V DC power supply. 1. Both LED1 and LED2 should not glow at the same time. 2. Buzzer should beep only when LED2 glows 3.Pin6 of u741, pin2 of 555, R3 and R4 should be shorted together.
My Photo sensor transistor is detecting the shadow at random.When I set the potentiometer for the current intensity of light and move a paper or hand in front of the unit it does not detect the shadow instead it detects the shadow at paritcular angle.I want to know whether this is due to the transistor L14G3 or I am calibrating the potentiometer in a wrong manner.
SIR I WANT TO MAKE SHADOW ALARM...SO PLZ HELP ME....GIVE ME ITS DETAILS...N SUGGEST ME HOW I CAN MAKE IT.......PLZ.....THANK U.......SEND ME THE DETAIL @ deeptisingh36@yahoo.co.in
finally I have finished this project successfully.I was wrongly connecting the L14G3 transistor.Now everything this is working correctly.There is one thing and that is the sensitivity of the photo transistor is very good in dim light and poor in bright light.Please guide me in this regard.
if i kept this ckt in dark room or if there is no light in that case sound will be continuously hear... so what modification i can do in the ckt to avoi this problem??????
That can be easily achieved by setting VR1 and or interchanging the connection pin2 and pin3 of IC1.
what is the comparison of that alarm?
My siren rings without the phototransistor . It also rings when IC741 is removed completely from the circuit. my connections are correct as per the diagram. PLEASE HELP ME PLEASE PLEASE PLEASE.what should i do?? Admin?? please help?????
can anyone get back to me please?? my circuit is continuing to work without the sensor itself. LED1 and 2 glow continuously. the circuit alarm siren rings whenevr the battery is connected. even if i remove ic741 the circuit is not affected. PLEASE PLEASE PLEASE HELP
Have you connected pin6 of IC1 to R3, R4 and pin2 of IC2 as shown in the circuit. Please check your connections again.
my project is not working properly. when connected to the battery led1 and 2 continuously glow and the alarm rings without the sensing transistor connected also. if i remove ic741 from the circuit it still continues to run like this. PLEASE PLEASE PLEASE PLEASE HHELLLLLP
Make sure that pin6 of IC1 is connected to R3, R4 and pin2 of IC2
it is good.i want to details like cost uses advantages & disadvantages of this project .so please send to my email immediately.please reply to me.
please give me the details of this project
it is good.i want to details like cost uses advantages & disadvantages of this project .so please send to my email immediately.please reply to me.
in shadow alarm ckttwo terminals of photosensor l14f1 connected.but left the one terminal.can anybody tell me how to connect the photosensor
sirits very hard to find L14F1 IC .could u tell me alternative of this IC?
sir i want to make this as my final yr project so plz help me to do so...suggest me how can i make it...
There is another circuit by Deekshith based on this. I have taken it for my project. Moreover the new circuit is more easily tunable than this. Worth Tryinghttpwww.deekshith.in201206shadow-counter-circuit.html
sir i want to know the estimated cost of shadow alarm...n can i modify this circuit for my final year project...
plz can anybody tell me where could i get l14f1 phototransistor
i want full documentation of shadow alaram