ThermalRunaway said:
...it's more common to put this resistor in series with the LED...
By that, do you mean like this?
**broken link removed**
Can you explain how that makes a difference? Isn't this resistor and this LED still on the same circuit? Does their placement matter?
ThermalRunaway said:
... But with the resistor value you've got there, you'll only get 8.5mA through the LED ...
I'm afraid I don't see why...
V = IR
V = 9 volts
R = 820 ohms
I = V / R = 9 / 820 = 10.9756 mA
What's wrong with the work above?
ThermalRunaway said:
If we assume a transistor HFE of about 150ish, and 8.3V dropped across the base resistors (leaving 0.7V for the base-emitter junction)
Can you explain how you can calculate the voltage drop across a single resistor? Particularly in this example?
ThermalRunaway said:
Can I ask, how did you come to those base resistor values of 470R?
I'm not sure anymore. I remember I had a reason
Well, what should be my criteria for picking a resistor in this situation? It would seem to me that I should aim to provide enough voltage and current to the resistor base so that current can flow from the collector to the emitter, but at the same time to limit it so as not to burn the transistor. Is there any other criteria applicable? And, I hate to ask for so much work, but can you please take me through this step-by-step? Or alternatively, please provide a link to a good, beginner-friendly article on the matter.
---
Yeah, sorry, I'm still a complete newb
I rented a copy of Electronics for Dummies at the library, but that book does not make me comfortable with designing
my own circuits at all. It has some cool projects, but it does not explain how they work.
I requested the classic (so I heard) Art of Electronics, so I'll have my hands on a copy within a week. By tomorrow, though, I should have Sams Teach Yourself Electronics (I think that's the name) in my hands. It's a nice and thick book, and that's probably a good sign.
---
Anyways, I'm sure I'll be back with more questions soon. Understanding electricity is hopefully a one-time deal. Once I get it, I won't bug you with such questions anymore