Bob's Minecraft Tutorial, linked by Billy ONeal, is a useful resource, but I'll try to put the basics into words.
How is it possible for the torches to
work as both input and output to a
circuit?
Is there a practical difference between torches on the ground and torches on the wall?
Depending on where the torch is placed, neighboring blocks will be inputs or outputs, but each neighboring block is EITHER an input or an output - no blocks are both.
- A torch on the ground (in other words, on top of a block) outputs power in the 4 cardinal directions, and also outputs power to any block in the air above it.
- That torch will only accept input from the level below it, so input wires must run straight into the block the torch is sitting on.
To summarize, torches on the ground output to their level and input from the level below.
- A torch on a wall (in other words, on the side of a block) outputs power in only 3 directions (it doesn't output back into the block it's mounted on).
- That torch will accept input from the top of the block it's mounted to, and from the other 3 sides of the block it's mounted to.
In summary, torches on a wall output onto the ground and take input through the wall block.
What if two torches are both acting as output to the same redstone-wire?
What if one torch is outputting positive/on/true to a redstone-wire but another is outputting negative/off/false to the same wire?
This has been answered elsewhere, but: If any power source hooked up to that wire is on, the wire will be lit up.
How do I read the diagrams on the minecraftwiki page?
Again, I'll try to break down the basics:
- White squares are just air, nothing special
- Yellow squares are blocks
- Dark yellow squares are blocks a level below (that is, they're an abbreviation for "white on this level, yellow below")
- Grey squares are blocks on the current level with other items a level below
White and yellow squares can then have these items on them:
- Red lines are wires
- Red circles are redstone torches (which may be attached to the side of a block or sitting on one)
- Grey circles are levers
- Small dark grey rectangles are pushbuttons
- Large grey inset squares are pressure plates
So, for example:
- a red line on a yellow background is a wire on a block
- a grey circle on a yellow background is a lever on a block
- a red line on a grey background is a block over a wire
- a grey circle on a grey background is a block over a lever
Within the MCRedstoneSim program you can change levels and see the wiring and such on each level of the circuit, but these extended types of blocks exist so that the whole circuit can be communicated with one set of symbols and no need to show diagrams per level.
I've made a video of a working example:
All you need are properly calibrated repeaters (4 ticks each), a "short-cut" for the door pistons and an inverter on one of the system parts.
Best Answer
The confusion lies in the fact that there are two different types of power a block can emit. These are sometimes referred to as strong and weak power.
Weak power is given to a block under the conditions mentioned in the question, by having wire on top of the block or pointing into it. This will unpower torches, extend pistons, play note blocks and turn on lamps & repeaters.
Strong power is given to a block by having a lever on it, a torch underneath it or a repeater pointing into it. In addition to the abilities weak power has, it will also power redstone dust in an adjacent block.