Connect with us

Burglar alarm.

Discussion in 'General Electronics Discussion' started by jacobi, Jan 26, 2018.

Scroll to continue with content
  1. jacobi


    Jan 18, 2018
    I'm working on a EKI project Burglar alarm. Project no.12.
    The directions don't tell how it works but it has an open 2 leads.
    It doesn't tell what kind of switch goes there. and also an optional place where you can have a buzzer at. Would that employ a loud speaker?
    At the open 2 enda would that go to a monitor of some kind?
    It has a scr a led 3 resisters a diode,not sure what value it has an a .1 MF cap.
    I wish I could find some info on this.
  2. Alec_t


    Jul 7, 2015
    Post the schematic, if you have one.
  3. jacobi


    Jan 18, 2018
    DSCF0001 (1).JPG
  4. ChosunOne


    Jun 20, 2010
    Deleted. Sorry. Can't help here.
  5. Audioguru


    Sep 24, 2016
    You need to learn about electricity and how an SCR works to see how simple that circuit is.
    One switch is shown as NO and the other switch is shown as NC. The NC switch can be a wire that sets off the alarm if it gets broken.
    The circuit applies the DC battery to light the LED and power a buzzer or siren when it is triggered, a speaker does not work with DC.
    hevans1944 likes this.
  6. Kiwi


    Jan 28, 2013
    hevans1944 and AnalogKid like this.
  7. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    I suggest you read and work the experiments in the order they are given in the book excerpt that @Kiwi posted. In particular, review Mr. Circuit Lab Kit A7 to see how an SCR works. This appears to be a "monkey see, monkey do" introduction to electronics with very limited "theory of operation" text. The "Lab Kit" seems to be aimed at those requiring hands-on instant gratification, lest they get bored and move on to Lego or Tinker Toy sets. Suggest you move up to more advanced publications, by Forrest Mims for example, to actually learn something about electronics. And visit here, of course, when you encounter something you don't understand.

    If no one has said it yet, @jacobi, welcome to Electronics Point!
  8. Wayne Phillips

    Wayne Phillips

    Jan 7, 2018

    An a alam system..mmm a good sign always were of her indoors.she has bites!
  9. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    I kinda like the "Protected by Smith & Wesson" sign, even though we don't actually use any of their products.


    But why announce to the world that you have "protection" of any kind? Let it be a surprise. Big dog = mo betta, mo bigger bites. We have a LOT of "big dogs" in our home, but none yet with four legs and fur since moving to Florida.
  10. ChosunOne


    Jun 20, 2010
    Okay, I was gonna keep quiet on this one because I looked at it as a hobbyist doing a project on a breadboard or something. Now that some of these guys are treating it as if you're actually trying to build a working burglar alarm system, I'm going to put in my 2 cents worth. I speak from over 40 years of experience in installing, servicing, troubleshooting and fixing burglar alarms, starting around 1975. Most of that time was spent in servicing systems, so I got a lot of experience with systems that were installed decades earlier. In that day, users tended not to upgrade every few years--they expected the systems to last, which most of them did.

    Building an practical working burglar alarm from scratch (our of simple electronic components). one that is intended to deter burglary from a home or small business, is not as simple as it looks from any electronic schematics you're likely to find in a beginner's electronics hobby book.

    The particular schematic you've referenced, for instance, doesn't even give a means to arm and disarm ("turn on and off" or activate/deactivate) the system, unless you're planning to remove the battery when you don't want it active. When you put the battery in--assuming the circuit board is inside the house, and any access door/window is on the protected loop--then you can't leave unless you add some extra circuitry to bypass a door to let you out.
    Arming/disarming and means of access are crucial to a practical alarm system and are missing in your schematic.

    Aside from that little detail, the schematic is one of the worst proposed designs for a burglar alarm that I've ever seen. It's understandable, because the EKI Project No. 12 schematic was designed to demonstrate the (hypothetical) use of an SCR rather than design a practical burglar alarm system.

    The Project No. 12 design, with an arm/disarm means and a sounder added, would be approximately the equivalent of an Ademco model-100 control and system that I used to work on, well into the '80's, but was first marketed before my time, I would guess sometime in the '60's or even the '50's, I don't know.
    The Project 12 design is simultaneously more complicated and less efficient, as well as potentially higher maintenance than the Ademco Model 100. I seriously doubt than anyone ever actually manufactured that design for commercial use. The Model 100 consisted of two relays and a key switch and lasted, for all practical purposes, forever (with battery replacements).

    I never saw a Model 100 fail--every replacement was because the user wanted some feature(s) that the 100 couldn't be (easily) modified to give. It's too primitive for a home alarm today, but might be considered suitable to install in an isolated shed, The control panel consisted of two relays and a key switch; and door/window protective loop switches and a sounder of some kind completed the system.

    @jacobi, if you're seriously trying to find a bare-bones, super-simple alarm system that you can build from scratch, let me know and I'll give you the best advice I can.
    Alec_t and hevans1944 like this.
  11. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    I think you have the correct perspective on this. It is obvious that the OP is a newbie and was having difficulty understanding the simple SCR latching circuit. I doubt we have helped much in that regard, but there is little we can do at this point. The OP simply needs to learn a lot more about electricity in general before trying to understand the particulars of a sophisticated semiconductor component such as an SCR. I sure hope the OP wasn't looking for a serious burglar alarm circuit!

    I am somewhat amazed at the recent progress in commercial burglar alarm systems. For many years the "industry standard" was the simple, dedicated, closed-loop, telephone twisted-pair, monitored system promulgated by ADT (Automatic District Telegraph). This "man in the loop" approach is still the best IMHO, but the trend today for home monitoring is to place that responsibility on the end-user rather than a on a paid monitoring service like ADT.

    We could create a whole new thread on burglar alarm systems, both commercial as well as practical DIY, but any such system (no matter how sophisticated) is worthless without a reliable human response, usually an armed response, to a trigger event.

    In the 1980s I worked for a company involved in highly classified national defense intelligence and reconnaissance systems. We had our own Faraday-shielded SCIF vault inside a building alarmed with ADT-installed sensors. A "silent alarm" triggered after the system was armed always resulted in a timed, rapid, armed response by BOTH ADT personnel and local police. In fact, they raced to see who would respond first. An ordinary private commercial business should be so fortunate!

    Today, if I choose to do so, I can get alarms directed to my cell phone and can video-monitor on my "smart phone" activity at the protected system location to allow me, rather than a paid monitoring service, to decide whether a call to local police authorities is appropriate. That goes a long way toward preventing false alarms and an expensive police or fire department response. Bells and sirens? Those are reserved for automobile alarms today and are universally ignored.
  12. Bluejets


    Oct 5, 2014
    I like the one where the burglar was confronted by somone calling from a dark corner "Jesus is watching and will punish you". Burglar calls back " who is that?" Voice calls back " it's Moses the parrot here". Burglar says "what idiot would call a parrot Moses". Parrot calls back " same idiot that calls a massive great rotweiler Jesus" !!!
    duke37 and Wayne Phillips like this.
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day