help starting analyzing circuits - Page 1
Forum section: electronics / beginners

author: user1868
author_rank: Newbie
timestamp: July 16, 2020, 05:22:34 pm
content: I am locksmith and have a pg21 exit alarm I can use. Could someone help get me started in analzying circuits? Ive been reading art of electronics to get going. I have attached some pictures. thanks.

author: user1868
author_rank: Newbie
timestamp: July 16, 2020, 05:23:54 pm
content: .

author: rstofer
author_rank: Super Contributor
timestamp: July 16, 2020, 06:15:59 pm
content: Trying to learn about circuits by studying a completed project for which no schematic is available is going to be very difficult (actually, nearly impossible).Trying to build up a schematic by following the traces is another complete waste of time. The chances of getting it right are essentially zero.You can identify big blocks like the tamper switch, the horn tone selection jumpers and other user accessible and adjustable components. In the end, everything goes into a microcontroller and the result is a tone output to the speaker.You could probably work through the power supply and you can probably find that the uC runs on 5V DC and that a large number of those resistors are used to 'pull up' various jumper or switch contacts. That is, the trace will be a 5V unless a switch or jumper is active in which case it will be at 0V. Tracing this around should be fairly easy. Clearly, you can trace the speaker connections back to the uC.There's quite a few components for such a simple device and that's because of all the adjustments - it's pretty much a universal exit alarm. To complicate matters, it looks like they scraped the identifiers off of the uC. That's fairly common and is done to prevent reverse engineering - sort of. It doesn't prevent it but it does make it more expensive in terms of time.I would think that the circuits in "The Art Of Electronics" (and the lab manual "Learning the Art of Electronics plus the "The Art of Electronics: The X Chapters") would be a comprehensive program. Personally, I would recommend starting a little lower with something like "Getting Started In Electronics" by Forrest Mims. The thing about "The Art of Electronics" is that it is used at MIT for EE classes, lower division, no doubt, but still by college students.I would recommend any or all of the Forrest Mims books as a smoother way to get started in electronics. Cheaper too!https://www.amazon.com/s?k=forrest+mimsAny book with projects is going to be more useful than a book full of equations and EE has a LOT of equations.If you like math, check out the Electrical Engineering track at KhanAcademy.org. Most people put that on back burner and their hobby is primarily 'cut-and-paste' of published projects. After all, it's the projects that are fun. Math? Not so much...https://www.khanacademy.org/science/electrical-engineeringIf you need help with math, Khan Academy is the place:https://www.khanacademy.org/mathYou really don't need a lot of math for hobby electronics. A wee little bit of algebra and some skills with a calculator are about all it takes. Study up on Ohm's Law, Kirchhoff's Laws, Thevenin's Theorem and Norton's Theorem and you just about have it covered. There are plenty of tutorials on the Internet covering these topics. But put it on back burner until you get further along.

author: Bud
author_rank: Super Contributor
timestamp: July 16, 2020, 07:42:05 pm
content: Quote from: rstofer on July 16, 2020, 06:15:59 pmPer the authors of the book, it was the other way around: the book was based on the materials used at MIT for classes.

author: rstofer
author_rank: Super Contributor
timestamp: July 16, 2020, 07:55:00 pm
content: Quote from: Bud on July 16, 2020, 07:42:05 pmEither way, chicken or egg, the material may be presented at a level that is inconsistent with a new hobbyist. Or not... I have all 3 volumes but they never really caught my attention. There was a study help thread running around here a couple of weeks ago. There is certainly a lot of support should a person become stumped. A search might turn up several threads.I don't learn well from lectures and reading doesn't do it either. I have to play with something and really see it work before I think I understand it. Measurements and traces work for me. To that end, my favorite gadget is the Digilent Analog Discovery 2 - it is absolutely perfect for learning electronics. Alas, it is fairly pricey and that limits it use by hobbyists. Students they have covered. Where else can you get a complete electronics lab that will fit in your backpack along with the laptop?

author: electronupdate
author_rank: Regular Contributor
timestamp: July 23, 2020, 04:01:32 am
content: The photos are not of good enough quality to really analyze in depth (see this great thread on eevblog on how to photo circuit boards:https://www.eevblog.com/forum/chat/how-to-make-decent-photographs-for-forum-postsarticlespublications/However, here are some things one can sort by looking at the photos:

author: samadamsuk
author_rank: Newbie
timestamp: July 24, 2020, 02:56:45 pm
content: So I'm the least qualified to answer this by an order of magnitudes!But - I can share with you the journey I'm on, as a newbie!!Step 1: Start VERY simple: Lots of online learning material to get the basics of circuits.Get your head round the basic components: Resistors, Capacitors, Transistors, Diodes etc- how you work out values in parallel/series, how they work in AC/DCStep 2: Don't get put off by the math - let it become intuitive and lay out some simple circuits on a simulator (Download something like SimulIDE to start with)Place as many Current and Voltage sensors around the created circuits to get a handle on whats going on as you need. For me this is the only way.Step 3: Once you are comfortable, start to get some circuit diagrams that are out there on the internet, that have good descriptions, and lay them out on a simulator (By thispoint, a more capable one like Simetrix) - see here for an example alarm circuit:http://www.zen22142.zen.co.uk/ronj/cots.htmlStep 4: Work out from there, eventually things that looked extremely confusing and took nights to wrap your head around (atleast with me anyway!) become second nature andyou can start to string together logic IC's, segment displays etc and plan and build your own alarm circuits.Hope that helps! Key message is go from simple principles upwards, and (I find) everything takes mental effort to compute in my head, but once worked out, it makes sense at a quick glance after that ...