Laser Security Alarm

I tried to make a circuit which is called "Laser Security Alarm". My problem is the buzzer is beeping even though it doesn't make contact with the laser. Can someone help me? The link below is the one that i try to make.

by Taz_29
August 07, 2018

1 Answer

Answer by mikerogerswsm

That's alright. The circuit is designed to beep when it can't see the laser. You need to adjust the pot so it is not beeping when the laser is there and does beep when the laser beam is interrupted. When it beeps it will go on beeping. Start with the laser absent and the pot turned so its wiper is hi and stop the alarm by pressing reset. Then add the laser and turn the pot until the alarm goes off. Turn the pot back a little and press reset again. The circuit is now armed.

+1 vote
by mikerogerswsm
August 08, 2018

Alternative method. Connect a high impedance voltmeter between LM358 output and ground. This should read lo when the laser is there and hi when the beam is interrupted. Adjust the pot so that this is so. Stop the alarm by pressing reset. Try to find a pot setting where the alarm works but is immune to other light sources. Fluorescent lights can be troublesomeand you may need to shade the LDR.

by mikerogerswsm
August 08, 2018

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