Hacks for Minecrafters: Redstone

You can power devices by placing the power source right next to the device, but you will often want to separate the two. To do this, you use redstone dust, which carries the power from source to device. Redstone dust that is carrying power sparkles and emits particles. If it is unpowered, there are no particles.

Redstone dust has some traits that can make moving a signal a bit tricky.

Every block that redstone dust travels, the signal strength it carries decreases. The highest strength is 15, and the maximum distance redstone dust can carry a signal by itself is 15 blocks. This means that if powered redstone dust runs for two blocks, its strength at the end of those two blocks is 13, because 15 (the maximum power) minus 2 (the power it lost) is 13. You can change the length a redstone signal travels by using a device called a redstone repeater.

You can’t place redstone dust on most transparent blocks (blocks you can see through) like grass and glass, or stairs or slabs. However, you can put redstone on upside-down slabs, (slabs placed in the top half of a block space), on top of upside-down stairs, and on glowstone.

Redstone can’t travel over bottom slabs or most transparent blocks. It can travel over upside-down (top half) slabs.

Redstone needs to point at a device or block in order to power it. If your trail of redstone dust travels by a device without pointing at it, it won’t power the block. The exception to this is when you place just one single dot of redstone dust and it points nowhere. This can power blocks to all four sides.

This single dot of redstone dust is “directionless,” because it’s not pointing anywhere. It can transmit power to all sides, so all three of these droppers are powered.

Redstone powers the blocks it is on and points to when it is active and lit up. It is said to do this weakly, because the blocks that are powered this way don’t have enough power to turn on attached redstone dust, but they do have enough power to activate repeaters, comparators, and other redstone devices.

Here, redstone dust sends the same power to two blocks. It is enough power to turn on an attached comparator (bottom) but not enough to turn on redstone (top).

To move redstone dust vertically more than one block, you need to use a staircase, so that it travels one block over for each block it rises. You can also use glowstone or upside-down slabs in an alternating pattern. Because these two blocks are both seen as transparent, they don’t cut off the signal at the block edges where they touch.

Three ways of moving a signal up: Upside-down slabs (left), glowstone (middle), and a staircase (right).

A fourth alternative is to use redstone torches in an alternate pattern. Because these turn the signal off and then on, you have to be careful that the final torch is on to maintain the signal.

These methods only work for moving a signal up. To move a signal down, you will have to use a staircase or create a special contraption. You can make a spiral staircase that takes up less space.

There are two devices you can use to change the power of the signal traveling along redstone dust. These are the repeater and the comparator, and they are very important parts of many redstone contraptions.

The redstone repeater takes a redstone signal pointed to its back and refreshes it to the full 15 power level. This allows you to carry a signal farther than 15 blocks. At the fifteenth block or earlier, before the redstone fizzles out, place a repeater pointing in the direction the signal is moving. There’s an arrow on the repeater that shows you which way it is pointing. There are also two mini-torches that light up when the repeater is powered.

The signal on the right is too long to reach the TNT. On the left, a repeater makes it happen.

Repeaters also can delay a signal. Traveling through a repeater delays the signal by 1 redstone tick. You can change this to a delay of 2, 3, or 4 ticks by right-clicking the repeater. When you do this, the back torch changes position to show the change in delay.

What’s a Redstone Tick?

A redstone tick lasts about one tenth of a second, and redstone contraptions measure and react to each other based on this unit of time. A redstone tick is twice the length of a game tick, which lasts one twentieth of a second. Game ticks are used in programming the game to measure and time events, like when plants grow.

A comparator is a bit like a repeater, and it looks very similar, except it has three mini-torches on it instead of two. Like a repeater, it has an arrow on it that shows the direction it is pointing. It takes a signal coming in from the back and compares it to a signal coming in at its side. The comparator outputs a signal that is the same strength as the back signal, unless there is a side signal that has greater strength. (There can be two side signals, left and right.) Then the comparator will produce no signal. This is called comparison mode.

The front torch of this comparator is unlit, so you know it is in compare mode. The side signal is stronger (it’s closer) than the back, so the comparator sends no signal out its front.

You can also put the comparator into subtract mode. To do this, right-click the comparator, and the front torch will light up. In subtract mode, the comparator will take the back signal strength, and subtract the greatest of any side signal. The signal it puts out is equal to the result. So if the strongest side signal is level 4, and the back signal is level 15, it will output a signal of level 11.

The comparator is in subtract mode here—the front torch is on. It subtracts the side signal (9) from the back signal (12), for an output signal strength 3. Enough strength to set off that TNT.

Comparators can also measure containers and produce a signal whose strength depends on how full the container is. You can read more about this in chapter 1. No signal is produced when the container is empty, and a full strength signal is produced when the container is completely full. Comparators can also measure a cake (how many slices it has), item frames (what position the item is rotated to), and cauldrons (how much water they have).

The cake on the left is whole with its full 7 slices intact. Each slice has a value of 2 (for cake fullness sensing). Its comparator sends out the maximum uneaten cake power strength of 14. The cake on the right has a slice taken from it. So its comparator sends out a cake power signal that is only 12 blocks strong.