I'm a beginner hobbyist, I'm trying to get to the point where I can look at a basic circuit (physical, not a diagram) and speculate on what it does. Transistors are confusing, because there's so many types and some are visually similar. Obviously I could google whatever I find printed on the side of them, identify the manufacturer, etc. Assuming I don't want to bust out my laptop every time I see a transistor, what I can I determine?
What I'm asking is what I can know by:
- Looking. It has 3 pins on one side, it's D shaped, rectangular with through hole, hat shaped, round, Size, notches on the side, Any rules like "If it's D shaped, it's always a BJT" (is that true?)
Testing. Things I can easily determine by poking it with a basic multimeter. Rules like "if there's high/infinite resistance between pins 1 and 2...". Whether or not such tests will work while it's in the circuit or if it needs to be removed to know for sure.
Id numbers. Are there any naming schemes that are in wide enough usage to bother with?
I'm putting together some notes I can keep in the garage with things like resistor color codes, the various things each component is called, their diagram symbol, what each pin does, etc. I hope this isn't too open ended, if I knew more I'd ask something more specific. I've found a lot of resources that explain the types, what they do, and their symbols, which is great for design, but I'm having a rough time finding resources that explain how to identify the type of transistor by examining the actual thing.