People who know their way around building electronics, and electronic parts?!?

Question

http://www.instructables.com/id/Protect-Your-Home-with-Laserbeams/

OK, Ive bought almost all the parts, Except the varibale transistor and the laser diode. Man, I thought this would be easier... On the Diagram, I dont know what any of it means. I'm looking for someone that I could E-mail through Yahoo answers with some of my later questions..

Here are the questions I have now, Ok, on the capacitor, there is just an arrow across it going from away from one lead, and towards the other. In the diagram Its done differently, Which side on my capacitor is the positive side? the one with the arrow leading to it? or away from it?

Also, It says you need a IC board.. I went out and bought a PC board, Am I stuffed? what do I do?

On my transistor, It tells me which lead is the collector, the base and the transmitter, but on the diagram its just a picture.. Which one on the diagram is the base? which one is the collector? and which one is the emmiter?

OK, Thanks alot in advance

Answer 1

You may be stuffed, the instructions are really not very good, but, yes, you can (probably) use your "PC" board if it is one designed for prototyping circuits.

I think that the schematic included in the video and the "steps" is very oddly drawn, plus it's just plain wrong, you need to use the schematic in the comments (scroll the page down a bit if you haven't already)

In the symbol, the emitter of the transistor is the one with the little arrow on it  (connected to the siren and the (+) side of the capacitor  in the CORRECTED schematic)

The base of the transistor is the line that is perpendicular to the vertical line in the symbol (connected to the intersection of the photocell and the variable resistor in the corrected schematic) and the collector is the remaining lead, (connected to (+9V) in the corrected schematic)

Does the arrow on your capacitor have (-) signs marked on it? if so the lead opposite the arrow is the positive.

I don't think this is a particularly good circuit, if it works at all (which I'm not so sure about) it will draw at least a milliamp of current, giving less than a month of battery life if used 24hr/day, and 9V battery are not that cheap.

Answer 2

When you say IC board, does it mean veroboard? PC Board is different from veroboard as the holes are predrilled.

Google the datasheet for the transistor, i.e. BC549. It will tell you the orientation of the Transistor and where the Base, Emitter and collector legs are.  What sort of Capacitor are you using? an electro cap will have a black line on the negative side, some caps are also no polarised.