A light activated alarm is built in this tutorial. When enough light falls on the LDR in this circuit, an alarm tone is played on the loudspeaker.
Light Activated Alarm Circuit Diagram
Tutorial 11: Light Activated Alarm
Starting Electronics Blog
Electronics for Beginners and Beyond
in wich program did you test it? i test the circuit in livewire and it doesnt work. what is the problem?
I did not simulate it in software, I built the circuit on breadboard and it works. Simulation software has its limits — build the real circuit to see if it actually works.
Can I try this on a circuit board?
Hi Aracely
Sure, any of the breadboard circuits can be built on a PCB or strip-board. You will just need to do the layout yourself.
I also had anothe question… I can’t seem to find the 100n capacitor, can I use a .1uf instead? And by any chance do you know where I can get a ldr. Cause all I have found are cds.
Hi Aracely
0.1uF is the same as 100n.
I got my LDRs from RS Components, but where to get them depends on where you live.
why is that it is not working on my circuit ive constructed it but doesnt work…can u please show some other videos..tia
Hi jnniln
At the moment I don’t have time to make more videos.
and also can i use .1mf 50v electrolytic capacitor?
Hi jnniln
The 0.1uF electrolytic capacitors should work fine. You can look at this circuit for connecting the capacitors the correct way around: http://startingelectronics.com/beginners/circuits/two-transistor-LED-flasher/
Can the loudspeaker be substituted for something smaller?
Hi Warren
You should be able to use a small PCB mount speaker or piezo element. Just check the rating on the device that you use and change the value of R5 if necessary.
Sir, i was making light activated alarm from article post on your website .
I made circuit with your articles guidance but its speaker sounding but it does not stops in absence of light . I have checked it many times but iam unsuccessful .
Can you please tell about me probable mistakes that i have done , as result its LDR is not working on the circuit board.
Please send me your answer as soon as possible. Thankyou