I don't understand why these have two transistors for each pin, unless that just allows them to amplify the voltage more.
Perhaps this is a bad idea.
I wasn't aware there was any difference between PNP and NPN besides the chemistry of the inner workings of the thing. Does it really make a difference, and why?
Yes it does. A PNP is an upside down NPN transistor. Emitters go to +ve not ground and collectors go to ground not +ve.To turn it on you need a difference in voltage between the emitter (now at +) and the base. So you turn it on with a logic low and off with a logic high. Exactly the opposite of an NPN.
but why did Ran say I needed to use PNP transistors to source the current? I don't get that.
Why can it only source OR sink?
In that last drawing the LED in the emitter is receiving sourced current BUT the voltage you can achieve for the source is only 0.7V less than the voltage on the base.
BUT the voltage you can achieve for the source is only 0.7V less than the voltage on the base.
There is no voltage gain in this configuration
At no point that I know of does a need for a voltage gain here,
Why would I WANT more than a drop of 0.7v
And what source exactly are you referring to? The emitter?