Laser Security System not working on Proteus Schematic

[FelixIG15]

Can somebody help/point out what's the mistake on this circuit?
The circuit is supposed to emit sound when the LDR isn't receiving any light. When i run the simulation on Proteus, it doesn't emit any sound at all when i turn off/on the light source. i tried changing the sounder to buzzer and speaker, but it still doesn't work.

The right LED(D2, the yellow one) ALWAYS turns on regardless of the state of the LDR, while the left LED ALWAYS turns on if i run the simulation when light source is on then if i turn it off during simulation, the red LED is still on. Vice versa, if i run the simulation when the light source is off, the red LED is off, then during simulation if i turn on the light source, it is still off.

I am asked to copy circuits or electronics from the internet and create them, so i'm not really sure how the LED should have worked.

I am very new to Electronics so please point it out as simple as possible.
Thank You

 

[betwixt]

You have the NE555 wired in monostable mode. It will only produce one pulse of output as the light level changes. I think you want to run it in astable mode and connect the output of U1A to the reset pin instead of the trigger. That way, it will oscillate when the reset pin goes to high voltage state. You need oscillation to drive a loudspeaker. Look at the data sheet to see the astable configuration and values to use.

The red LED should change on/off when the light level on the LDR changes. The amount of light needed will depend on the setting of RV1.
The yellow LED may never light with a loudspeaker connected, you would have to be fitted with its own series resistor from the top of R5 to ground.
Note that in real life you would also need a capacitor across the output of U3 and another across the input of U3.

Brian.

 

[Nik_2213]

Slightly off topic, related laser systems are often used as smoke detectors.
==

On our site, one sprawling production building's vast roof space held huge aircon systems etc etc. Also, much data and power cabling, so contractors and sub-contractors often accessed it.

One day, the secondary, laser alarm sounded. Its beam ran about a metre below the long roof's apex, was a back-up to the many individual 'smoke heads'.

As you'd expect, the site fire team responded at 'best speed' while the building's many occupants evacuated and a 'Three Engine' call went out.

The site fire team arrived on scene to find a group of sub-contractors having a picnic lunch, smoking and playing cards.

They'd bypassed the nearby smoke detector heads, but the infrared apex laser was a completely independent system, to be sure, to be sure...

Tampering with safety systems ? Food / Food consumption outside designated safe areas ? Smoking on site ? Gambling ??

They'd ALL sat through the videos, passed the quiz and signed for our site's strict safety, hygiene & security briefing...

Totally Epic Fail.

Aided by the fire team, site security marched those ijit sub-contractors to site perimeter, dumped them on the verge outside the gate.

Their company was barred, and their contractor nearly went broke as word of the incident went around...