Guys, I think he's not trying to "cheat" and have people design his circuits for him, I think he just doesn't understand how it works. (If he just wanted people to design his circuits he'd probably just take Eric's first schematic and submit that; I think he was asking for more examples to try to understand better...)
I suspect he mostly doesn't understand transistors, though I'm just guessing... Or perhaps he didn't understand relays *shrug*. And as for the rest of it, is it so unbelievable that they might simply have
not taught him well?
It seems pretty obvious to me that the quality of electronics education varies
hugely between countries.
AND_ECE, do you understand roughly how a transistor works? You know that if a little current is made to flow through its "
base" lead (that current then comes out of its "
emitter"), the transistor draws lots more current through its "
collector" lead (which also comes out of its "emitter" too)?
There's a lot of stuff about transistors on the internet. If you don't understand transistors, you should read some of these, even though they're not about making burglar alarms
Here's one transistor tutorial, it also says about LEDs. It's a bit long.
http://www.iguanalabs.com/1stled.htm
Another page with some info:
http://www.kpsec.freeuk.com/components/tran.htm
This page is VERY GOOD:
http://www.williamson-labs.com/480_xtor.htm It should make things much clearer about how they work. It has lots of diagrams.
Eh, you also mentioned "phototransistors". Those are a kind of light detector. When light shines on them, they draw a little bit of current through them. I don't have any diagrams or tutorials right now, but there are some out there if you look!
If you're still confused, perhaps you could be more
specific about what exactly you don't understand, like Eric said?