Laser Beam Alarm System with Rechargeable Battery for Laser

Step 4 Schematics Part 2, the LDR and Alarm Circuit.

This schematic is much larger and contains a lot more components than the first one. What Im going to do is break it down into two halves and explain how each works. If you have experience with putting together schematics feel free to skip ahead to the image of the final schematic where you can get right to assembling.

For those that want more help continue to the next section where I will explain the first part of the schematic, the LDR part. For those that just want to start assembling, a schematic of the final product is in the image bellow.

Comments

[luudvig]

Yes, by putting a electrolytic capacitor in paralell with the buzzer

[Kryptonite]

Would it be possible to make it so that the buzzer bit only goes for around a second?

[Kryptonite]

Going to hook it up to a nerf dart shooter for an Indiana Jones style walk way.

[revhead]

That sounds cool!
what I suggest is you do is scrap everything after the relay from my circuit and use the relay as your switch, just replace the nerf dart gun switch with the relay. If your nerf gun doesn’t have a power supply then you would need to connect a power supply in series with the relay and the nerf gun. Hope this helps. If you need any help or get confused just message me and I’ll try to help. 

cheers!

[III ScYThE III]

thanks mate I understand now. If it weren't for you I'd fail, my electronics teacher is useless.

[revhead]

haha, no worries happy to help. CHEERS!

[III ScYThE III]

I'm doing this for a school project in electronics and i really don't understand the reed relay part and the variable resister part (it has 3 leads and u only seem to use two) could u please show me somehow how these two things work?

[revhead]

ok first of all, the variable resistor. With most variable resistors there are three leads. For example a 10k ohm variable resistor has two leads on the end and one in the middle. if u don’t want it to be variable you connect the two outside leads to your circuit, but if you want it to be variable you need to hook up the middle lead and one of the end leads, so basically you need to hook up the middle lead to one side of the circuit and any one of the outside leads to the other side (only 1 of the outside leads, not both, u will end up with one lead on the outside not being used) The reed relay is built into a nice small package but is actual two parts, a little glass tube with bits of wire inside (like a tiny switch) and wrapped around the glass tube is alot of wire. The relay has four leads, one on one side and three on the other. The one on the end is one side of the glass tube and the other side of the glass tube is in the middle of the three leads. So, on the alarm side of the circuit you connect the one lead on its own and the middle lead of the three leads. On the LDR side you need to connect the two outside leads left over. The reed relay you buy will probably be different so u need to check the code on the side of it. Google this code and you will surly find a web site that has a picture of what each lead does. This is a lot of info and will probably be confusing. Just let me know if you need any help. Happy to help you out, cheers

[jezznar]

hmmm I'm wondering if you can change the 3rd module(alarm/buzzer part) into something like a motor circuit. I wanted to try and interface it into a door lock.

[revhead]

That’s a sweet idea!! I think if you were to choose the motor wisely, perhaps hook it up to a gear box for greater torque it would be achievable. This would be so cool say on a bedroom door where all you need to do to open it was to walk past the beam or place your hand through the beam to disengage the lock. You could also make a spring mechanism to push open the door when it was unlocked. I like your thinking, very smart. Thanks for the comment, don’t forget to rate it!!

[jezznar]

Yeah that's a nice idea! Thanks! well I'm really new to all of these stuff. I'm still exploring how things work on motor circuits and currently studying them. Thanks for the appreciation! And I love your instructable! <3

[revhead]

thank you for the rating!

if you are interested in motor control you should check out his Instructable for motor speed control:

http://www.instructables.com/id/Simple-and-dirty-Pulse-Width-Modulation-PWM-Wi/

I am currently making a Laser Spirograph using three of these PMW (Pulse Width Modulation) motor control circuits. it is very easy to follow and works great. I'm new with motors as well and making this PWM circuit has taught me alot, and I'm sure you will also learn alot.

Cheers!!

[jezznar]

cheers! =) thanks =)