I just read the latest Blog entry on the site regarding creating a break-out board like a Gertboard and wanted to understand more about the Zener diode component and how exactly that is supposed to work.
From my understanding of the schematics, each GPIO from the RasPi gets connected through a serial resistor (330 ohm? or my units wrong?) to the breakout board GPIO socket. That way, whatever you plug into the breakout board GPIO socket has it's current limited, even if you short it to ground, because of the resistor.
So where do you plug the other lead for the component you plug into the breakout board? Just that just go to the GND connection of the RasPi? Is that basically where the other lead of every component eventually goes to complete the circuit?
Now regarding the Zener diode, it looks by the schematics that it is connected to the GPIO as well, just before the resistor it branches off and the other lead goes to the GND as well. So it is connected the reverse direction. So if your GPIO is "high" won't it put out 3.3v and isn't that the threshold voltage for tripping the Zener the other direction, causing it to ground and therefore it would bypass the circuit you are intending to send voltage to... like the resistor-LED combo?
And then how is it that it allows you to use it as a GPIO input? I still haven't figured out whether GPIO inputs are also considered "high" and "low" only or if you can actually read incremental voltages, and what the range of voltages are that it will accept and current supply, and I haven't seen any examples.
Any help understanding the protection circuit with Zener diodes, how it works for GPIO in/out and what a GPIO input would actually be reading would be greatly appreciated! Sorry for the noob questions here but I am new to circuit electronics!