[SOLVED] having problem with laser alarm

[jepoy12]

hi, Im currently making an Laser alarm using the 741 op-amp as a comparator.
heres the circuit.

but then I came up with a problem. If I put the laser beam directly to LDR and a moving object(for example like man) moves in across the laser it will only buzz if ever he/she will stay and block the beam hitting the LDR. What I wanted to do is when an object PASS unto it, it will then trigger the alarm and start buzzing and it will only stop when someone hit the reset button. so I start searching on how to make that possible then I saw this video showing the one that I wanted.

How to make a Laser Alarm with a 741 op amp and a 4017 timer - YouTube

I tried to connect my 741 dark detector to his 4017 decade counter and follow his schematic.
and the result was the buzzing wont stop even if I hit the reset button. but all works fine like what I want only the reset is not working.
help me please anyone.
thanks.

 

[kak111]

Try this simple solution for hold and release alarm.

 

[jepoy12]

if someone triggers the alarm will it makes the buzzer buzz until I hit the switch?

 

[vimalkhanna]

Add an IC 555 before the 2222 for converting this to a bistable .Once the alarm hits ,it shall remain ON till you reset the bistable .

 

[ALERTLINKS]

You can use a small SCR instead of transistor, once triggered have to reset.
Or use this circuit. The two transistors act as SCR.

 

[jepoy12]

yes it all works but its not what I really wanted to do.
I wanted it go continues buzzing if someone only PASS at laser beam that triggers the alarm. then hit the reset to make go back to its normal state.

thanks for all the help but its not really what I want.

---------- Post added at 12:42 ---------- Previous post was at 12:39 ----------

Add an IC 555 before the 2222 for converting this to a bistable .Once the alarm hits ,it shall remain ON till you reset the bistable .

but if you get the thing blocking the beam to the LDR the buzzing sound will stop.

 

[ALERTLINKS]

I wanted it go continues buzzing if someone only PASS at laser beam that triggers the alarm. then hit the reset to make go back to its normal state.

This circuit will behave as you have asked for. It has a push to make switch to reset. If someone only PASS at laser beam that triggers the alarm and it go continues buzzing. It has minor modifications to your original circuit. I posted ealier, i thin you didn't tried. Now i added reset switch for clearity.

 

[jepoy12]

what kind of PNP transistor do I need to use for it?

 

[ALERTLINKS]

Any general purpose transistor available in your local market will do.

 

[joemnice]

does it worked?

---------- Post added at 10:00 ---------- Previous post was at 09:51 ----------

do anyone have tested it?

 

[ALERTLINKS]

Its is marked [solved]. Probably its working.

 

[jepoy12]

Yes, all their suggestions worked.

Thanks to them I even made a better one on my own.

 

[joemnice]

but i have a question,, im just a newbie in electronics,..

what is the connection between the pin 3 of IC in 100K resistor (R2) are they parallel or in series? thanks for help

---------- Post added at 06:02 ---------- Previous post was at 05:58 ----------

is that a potentiometer or what?

can i use SCR instead of two transistors?

 

[ALERTLINKS]

Pin #3 is connected to center leg of 100K potentiometer (variable resister). It is used to adjust sensitivity. You can replace three transistors with a single thyrister.

 

[joemnice]

three or two? thanks.. im going to try it to multisim to test it..

 

[ALERTLINKS]

Sorry its 2. If you need a beep for certain time, see this link
Light-sensitive Alarm Project
Light detectors,
**broken link removed**

If sensor attached to input, this circuit can serve both purposes,
**broken link removed**

 

[joemnice]

@jepoy12

can you send here or to my email the schematics of your improved alarm? thanks...

---------- Post added at 12:36 ---------- Previous post was at 11:22 ----------

anyway,, if possible,, can you send me the schematics of that in EAGLE cause i dont know how to use it.. thanks

 

[wahabqamar]

THIS CIRCUIT DOESN'T WORK
AUTHOR'S CIRCUIT ALSO DOENS'nT WORK
THANKS FOR WASTING MY MONEY AND TIME:evil:

 

[jepoy12]

**broken link removed**

 

[papunblg]

hi, Im currently making an Laser alarm using the 741 op-amp as a comparator.
heres the circuit.

but then I came up with a problem. If I put the laser beam directly to LDR and a moving object(for example like man) moves in across the laser it will only buzz if ever he/she will stay and block the beam hitting the LDR. What I wanted to do is when an object PASS unto it, it will then trigger the alarm and start buzzing and it will only stop when someone hit the reset button. so I start searching on how to make that possible then I saw this video showing the one that I wanted.

How to make a Laser Alarm with a 741 op amp and a 4017 timer - YouTube

I tried to connect my 741 dark detector to his 4017 decade counter and follow his schematic.
and the result was the buzzing wont stop even if I hit the reset button. but all works fine like what I want only the reset is not working.
help me please anyone.
thanks.

Which software is used to create that animated circuit diagram