Question about DIY laser alarm?

[DMaldonado93]

Hey guys. Im new to this forum and I was looking for a bit of help from some people.

I am trying to make a simple laser trip alarm and so far I have gotten it to go off with a change in light by using a photocell. I attached what I got so far. Right now it will go off when the plane is broken. But I want it to stay on to be able to see if the alarm was tripped. Now if it is possible I would like to make it so that the LED and buzzer will stay on until you press a button to reset it. Now my question is how would I go about doing that? If anybody has a schematic it would be great but I am fine with people just letting me know how to incorporate the push button switch
to reset the circuit


View attachment 64895

 

[ericgibbs]

hi,
You need some form of 'latch' on the output of your circuit. You could use logic IC's or a self latching relay contact.

Whats the supply voltage to your project.?

 

[DMaldonado93]

I am using ac adapter supplying between 9.5 and 10v

 

[ericgibbs]

I am using ac adapter supplying between 9.5 and 10v

hi,
Looking at you bread board circuit I cannot see a resistor in series with the Green LED.? I would suggest a 390R or 330R.

I will draw a simple circuit and post later. Do you have any type of logic IC's etc in your stock.??

 

[ericgibbs]

hi,
Look at this option.

On the plots the light is increasing from left to right.

If you need to change the sense of the output change over the input pins of the 4093, [ let me know if you dont follow]

 

[DMaldonado93]

U lost me on the schematic. lol What components are the U1 and U2? and I dont think i need a resistor in series with the LED because it lights up with changes in the light but i think its because I have a buzzer in series with it. and as fa as ICs i only have two LM741 and one that says HM9102D

 

[ccurtis]

It would help to know the part number, or light/dark resistances, of your photo cell to get the resistor values just right, but you can try this circuit and see how it works out too.

 

[DMaldonado93]

I'm going to try the second schematic later today. But I have another question im thinking of redesigning this. I want to be able to trip the alarm but only when a certain item crosses the field. I am making this for beer pong and I want it to go off when somebody's elbow crosses the line but i want it to be able to let your hands cross but not your elbow. So I was thinking of making some kind of elbow band to have it trigger only when the elbow crosses. Can anybody help me out with how to do this???

 

[gtr_stitch]

I did pretty much the exact same thing you're trying to do. Hope this helps!

If you want, you can replace the 555 circuit with an led. Works just the same.

Edit: Sorry about that. Kinda jumped the gun there. I guess I didn't have what would have helped, so I drew one. Use an SCR. Also, the value of R1 should be higher than the LDR when you have the laser shining on it, that way the voltage wants to go through the LDR rather than R1, and when the beam is broken, power goes through R1 and trips the SCR, which stays on until the power is cut, like with a switch. The first circuit I showed with the 555 was a light detecting circuit, but with a little switching around can work as a dark detector. Have fun!

 

[Firecell]

Laser Alarm

Hi I am new to electronics. Please help me in building a laser trip alarm system for my home. I have fied input voltage of 24V DC. Which equipments I should use? and how should I connect it with eachother. Also if possible draw a circuit diagram for it. Thanks in advance