Noob schematic reading questions

[itchyfingers]

Ok, I've built a few kits from BYOC and GGG, now just started trying to build some simple projects from schematics and had a couple of questions I was hoping you guys could help with...

Pots - I get that a resistor symbol with an arrow pointing at it is referencing a potentiometer, but how do I know if the pot should be linear or audio from the schematic?

Trannies - I get the difference between NPN and PNP symbols but how do you know which leg is the emitter, collector, and base from the schematic?

IC's - I can tell a triangle symbol is for an IC, but which pin is pin 1 on the actual IC (is it the one to the left of the notch?), and then how do they get numbered from there?

I'm sure I'll have more, but these are the big ones for me right now! 

[phector2004]

1. Often, it will write A or B after the resistance. A = "Audio" or Log. Your ears hear loudness in a logarithmic fashion. I usually find these on volume pots. B = Linear, I see these more often. Doesn't matter THAT much if you swap, but you'll be compromising your control (harder to dial in the "right" amount if a little twist makes a lot of difference or vice versa)

2. Usually, the middle one is the base. I then look at the vertical line on the symbol and it corresponds to the flat part of the transistor. NOTE: NOT ALL TRANSISTORS HAVE THE SAME PINOUT FETs have funky pinouts, I find.

3. Its the one with the circle. Numbers go around it.

Good luck, enjoy

[itchyfingers]

Cool, thanks Phil!

I'm cool with your answers for 1 and 2, still sorta befuddled about the IC.  So if the circle is 1, then do the numbers play out over the other pins like a clock -

1  2
8  3
7  4
6  5

or do the numbers go down one side and up the other?

1  5
2  6
3  7
4  8

[phector2004]

counter-clockwise

http://www.kpsec.freeuk.com/components/ic.htm

but I usually just look at the datasheet, and it shows which actual pin does what

[itchyfingers]

Figures, the one configuration I didn't think of!  Awesome site, btw.  Thanks again Phil!

[JKowalski]

NOTE: NOT ALL TRANSISTORS HAVE THE SAME PINOUT FETs have funky pinouts, I find.

Bipolar transistors and MOSFETs are in the order COLLECTOR/DRAIN, BASE/GATE, EMITTER/SOURCE

JFETs go in the order gate, source, drain.

These are often flipped 180 degrees for different transistors (you can't always tell by using the rounded/flat side as a reference) So be careful.

Power transistors are different.

Power bipolars/MOSFETs are usually in the order BASE/GATE, COLLECTOR/DRAIN, EMITTER/SOURCE from left to right looking at it from the front.


Knowing this speeds up the PCB making process since you can (usually) put down your transistors without checking the datasheet first - as long as you know which terminal the middle is. After you make the board, you can put the transistor in either way, so you then take a peek at the datasheet. Unless you bought some really funky transistor.


REMEMBER, there are always exceptions to these pinouts

[phector2004]

yup,

2SK117's are Source-Gate-Drain 
gotta rewire everything if I wanna swap in a J201

Also a neat observation for pots:

If you're looking at it with the shaft up and the tabs facing you, you can number them 1,2,3 going left to right. When you turn the wiper clockwise, you're lowering the resistance to terminal 3 (the top one in a schematic), and bringing it counter-clockwise you're increasing the resistance to terminal 3 (lowering the resistance to terminal 1, the bottom one in a schematic.

Hope that makes sense, I still sometimes wire them backwards!

[itchyfingers]

That does make sense.  I am still having a tough time in my head of seeing "through" the board / schematic, but I am learning!  You mention the "bottom lug in the schematic" being #1, and that got me to thinking.  I've seen a few schematics that call for an electrolytic cap to bridge the lugs on a pot sorta like this guy:



Based on what you said about terminal 1 being at the bottom in a schematic, is it safe to assume the 47uF electrolytic cap should connect lugs 1 and 2 of the 5k pot since its at the lower end and middle of the resistor symbol?

Again, thanks for all your help, guys!

[phector2004]

yup, so looking at it from the bottom, it should connect + side to the wiper (middle) and - to the 1st lug (right one looking at it from the bottom side, facing you)

[Ice-9]

Transistors and Fets have many different pinouts so its best to look up the datasheet for specific pinouts.

[itchyfingers]

Phil - thanks again man, I appreciate the guidance. 

Ice-9 - do you have a website you use to check these datasheets, or do you just google the transistor or FET name?

[kaboom]

Hey! I recommend http://english.electronica-pt.com/db/cross-reference.php?ref=AC139 (yeah, that's an example of the AC139) .Some parts are in spanish but the important things aren't

[edvard]

Yes, Googling for parts numbers works pretty well, but http://www.datasheetarchive.com/ has had 90% of what I needed to find, so you might as well start there.

[itchyfingers]

You guys kick major ass!  Thanks for all the help. 

[Ice-9]

Yes, Googling for parts numbers works pretty well, but http://www.datasheetarchive.com/ has had 90% of what I needed to find, so you might as well start there.

+1 on the datasheetarchive, i use it all the time

[newfish]

+1 also on Datasheet Archive.

Add it to your internet favourites list and you won't go far wrong.

[edvard]

Lately http://www.alldatasheet.com seems to be a help as well.
Now you're armed to the teeth...

[IvIark]

Based on what you said about terminal 1 being at the bottom in a schematic, is it safe to assume the 47uF electrolytic cap should connect lugs 1 and 2 of the 5k pot since its at the lower end and middle of the resistor symbol?

All that scheme is really telling you is that both lug 1 of the pot and the negative leg of the capacitor are connected to ground.  Some people don't like connecting components between the lugs of the pots especially for a value like 47uF which could be a physically large capacitor, so if you were making for instance a vero layout based on that scheme, you could put the cap on the board with the negative leg on the ground rail, and then wire from lug 2 to the row you put the positive leg of the cap.  And lug 1 of the pot would be connected to any point of ground.