[moved] Laser Alarm with timer and reset?

[MNorwell]

Hi, I'm a newbie and I'm not an electrical engineer but I can read the circuit diagram. I saw some circuit diagram of laser alarm with timer and laser alarm with reset, but there's no diagram of it with the combination of timer and reset, would you help me to create a diagram with that combination. TIA.

 

[chuckey]

Re: Laser Alarm with timer and reset?

A laser emits light, so it cannot alarm (think of a torch). The reflected light from a laser can be detected and the breaking or reduction of the received signal can be used to fire up an alarm.
The main problem is at the receiving end. The photo detection device will always saturate, which means that if the suns rays get into it, it will always think the laser is on even when its not. Street light and vehicle light can also have a similar effect. So to reduce this effect, the laser should be switched on and off rapidly, say 1000 times a second,, so the receiver looks for this rapidly changing light and tends to ignore others.
So the optical path needs to be sorted out with lens and tubes to stop extraneous light getting to the photocell to avoid saturation.
So now you have some sort of photocell with a small varying output, this needs to be amplified and filtered so that only 1000HZ gets through it and its at a reasonable level, say raising it from 1mV to 2V. it is then turned into DC and its absence is used to trigger a timer and an alarm. When the timer times out, the alarm is stopped.
This is a guess at what you were thinking. Can you tell us what you want?
Frank

 

[MNorwell]

What I meant was laser security alarm, I saw some circuit that used ic 555 for timer and some circuit used ic 4071 for reset. What I want to ask is, is it possible to combine two ic (555 and 4017) in a circuit to have the laser security alarm a timer and reset.

 

[d123]

Hi,

If you can, post an image of, or the links to, both circuits you are describing (555 timer circuit and the 4017 reset circuit), otherwise it is quite difficult to imagine a solution to your question as the original circuits are unknown/unseen.

Thanks.

 

[MNorwell]

Hi,

If you can, post an image of, or the links to, both circuits you are describing (555 timer circuit and the 4017 reset circuit), otherwise it is quite difficult to imagine a solution to your question as the original circuits are unknown/unseen.

Thanks.

Thanks for your response sir, btw here's the diagram using ic 555 for
laser alarm with timer

And here's the diagram using ic 4017 for
**broken link removed**

I hope will help me. TIA.

 

[betwixt]

The design has nothing to do with lasers, it just a light detector. it would work equally well with a flashlight or daylight.

You can combine the circuits but the one with the 555 should reset itself anyway. The 555 timing components decide how long it operates for when triggered by the change in light level. If you have built it and it doesn't work, the reason is there are two components missing from the diagram, there should be a capacitor from each side of the regulator to it's ground pin. Without them the 555 would likely keep resetting itself randomly.

The design with the 741 would need a supply voltage in excess of about 9V to work properly.

Brian.

 

[d123]

Hi,

Brian is right, the 555 circuit should operate for a defined time then reset, the 4017 circuit could be considered a redundant add-on due to this.

Other options are: 2 555s, when the alarm triggers monostable timer #1 sets off astable timer #2 for a limited amount of time, so the buzzer goes off and on in the way a siren or alarm clock does.

If you really wanted to combine both circuits, but being honest I see no worthwhile point in doing that, you could use a 555 time delay circuit to trigger the 4017 reset button after x number of seconds, to turn the buzzer off.

**broken link removed**

This gentleman has some great circuits - he briefly explains what should happen and better yet the circuits work (he doesn't post silly or bad not working circuits), and a page dedicated to 555 circuits, I recommend you have a browse as you might find a nice circuit to use that fulfils the function you want of triggering an alarm and then resetting it. A couple of 555 and 4017 circuits appear there, but can't remember where.

If you want a light-triggered alarm, one method is an IR LED and what I think is a photodiode (IR barrier circuit).

 

[MNorwell]

Thanks for your replies.

I just wanted to build a laser security alarm that buzzer turn off in a certain of time when no one can hit manual reset. My real problem is, I can not create a diagram like that. Would you help me to create a diagram for that so I can start building my own project laser security alarm.

A laser security alarm that has a timer to stop the buzz in a certain of time or can manually reset to stop the buzz.

- - - Updated - - -

In this circuit diagram,



is it possible to put a manual reset?

I want to build a laser security alarm that will stop the buzz automatically in a certain of time (for example about 2 minutes) when no one can hit the manual reset.

 

[d123]

Hi,

If you only want to add a button to turn off the buzzer, then you can do it this way:



Sorry for Painting on the image, a quick way of drawing it...

If this is a battery-powered circuit, while the 7805 is a great regulator, you will find the circuit will work longer before needing to change the 9V battery if you change it to any suitable 5 volt (fixed voltage) Low Dropout Regulator - if you do this, there are a lot to choose from so try to select one that says it can operate from up to 9 volts at least and is capable of 1 Amp output, or 0.5 Amps.

You can use a 7805, but when the battery voltage drops to about 7V, the circuit may work a little erratically as the regulator will no longer be regulating its output voltage - it needs at least 2 volts above 5V to function correctly and regulate the 5 volts output, that is all.

For about 2 minutes, if you use a 6 million ohm (6 MegaOhm) resistor and a 22uF capacitor it really would be a preferable combination compared to using whatever resistor is in that circuit and the 220uF capacitor it shows. Or 1.2 MegaOhm and 100uF if you have to use a large value capacitor.

 

[MNorwell]

Sir, what I want for my project is, if someone crosses the light beam, it will alarm constantly but stops in alarming until someone hit the reset button OR if there's no one could hit the reset button it will automatically stops after 2 minutes of alarming. But I don't know how to create a diagram or what electronic parts need to use.


In this thread, he built a laser alarm that can stop using reset.
Laser alarm with reset

While in this circuit, there's a 1m bleep duration.
Light alarm
I don't know how he did this, but that's what I want for my project and I don't know how to apply it.

Could you give me a circuit that I want for. Laser alarm with timer and with reset button. Please?

And honestly, I couldn't understand some of your explanation. I just want a circuit diagram, because it's the only thing that I could understand.

 

[MNorwell]

If someone crosses the laser beam, it will trigger the alarm and I want it to trigger a 555 monostable timer that resets itself after a time duration (or reset it manually using reset button).

Could you give me a circuit diagram for that? and list of parts that I need to use.

 

[d123]

Hi,

Okay, the schematic you have for the 555 laser alarm/light activated alarm is one you can use. Post #9 shows how to add a button to reset it.

Change R1 from 10k to 1.2 MegaOhm and C1 from 220uF to 100uF for it to be 2 minutes on (after about two minutes it will turn off).

I have no experience of laser barriers, apart from seeing gimmicky music videos and sci-fi/James Bond films, I think normal people and machines use IR barriers.

Look for IR barrier circuits - one IR barrier circuit will name both LEDs needed, I do not know specific models.

As you already have the circuit and it names the components, you can see almost all the parts you need - you only need to look for the IR LED which transmits and the photodiode which receives, and replace the torch with one and the LDR with the other. And research the subject a little bit, maybe, so you understand what you are trying to make.

If there are electronics parts shops where you live they will no doubt gladly help you select the two unnamed components for the light barrier, if not there are many online electronics parts shops, often advertising on this web like Digikey, Farnell, Mouser, RS-Online, if not e-bay and so on.

- - - Updated - - -

Hi again,

If this is needed, not wanted to be made, and you sound like you're in a hurry if you don't mind the observation, it could be an idea to buy a pre-made one, it might save a lot of slow, sometimes frustrating and confusing making, and learning that a perfectly correct schematic may need fine tuning of several component values by each person who makes it.

This one works on 12 volts, and can be set from 1 second to 180 seconds, but has no reset button:
**broken link removed**

This one has a buzzer, is a good price, works on 9 volts, and you can buy the kit to solder the components or buy it already made, but it has no timing feature or reset:
https://www.quasarelectronics.co.uk/Item/velleman-mk120-ir-light-barrier-kit

I have the second one, and it works fine over a short distance (about 1 to 1.5 metres maximum).

If you decide to get the second one I will happily draw the schematic so you can put a timing feature and a reset button between the circuit and the buzzer, using a 555 and 1 pushbutton - because I know how to with this specific circuit. The first one has the timer, but it has no buzzer and would be a little harder to place a reset on it I imagine, so would not like to try to modify it.

Okay? It's the best I can suggest for now, sorry I am unable to offer a better solution.

 

[MNorwell]

No sir, I already figure out your modification in your post at post#9 and changing the value of resistor and capasitor. Now I can start my own project. Thanks a lot for your help. But if you would draw a schematic of the second one, I will use it as well. Again, thanks for your help sir d123, you gave me a very helpful info.

 

[MNorwell]

Sir, I started to buy some of the components for my project. When I buy the capacitor, they asked me the volt value.

My question is, what volt of 100uF and 0.1uF capacitor do I need for this project? TIA.

 

[MNorwell]

Hi, please disregard my last post about voltage rating of capacitor.

My question now is, can I use an adapter instead of 9v battery as a power supply? Or should I modify my circuit to be able to use an adapter? What adapter should I use?

 

[d123]

Hi,

You could use an adapter rated for 9V DC (or even 12V DC) and 1 Amp. If you use an adapter instead - which is better as the battery probably wouldn't last long - and it has a round, hollow connector, you may/will also need to get a DC connector/adapter (sometimes called "barrel jack"). If you get the 9V adapter plug where they sell the components, then ask for the connector at the same time.

N.B. with both the connector and the plug/9V adapter, check the polarity of the adapter and wire the connector to fit in with this. Often the inside is positive and the outside is negative, but not always, and some have swappable connectors that can be reversed if connected either way round that is possible. Pay close attention to this aspect, as you wouldn't be the first person or the last to fry a circuit if you don't double-check before plugging your circuit in. Also, a simple glass fuse that costs $0.50 in a pcb fuseholder that also costs about $0.50 or $1 on the barrel jack positive output line is good insurance against several possible problems.