40d:Lever

Either a lever or a pressure plate, once linked to one or more devices (doors, traps, or whatever), can act as a trigger, an activation mechanism for that secondary system. The two are activated differently, but the connected system is activated just the same. One system can have more than one trigger linked to it, and one trigger can be linked to more than one system. Once linked, a trigger must be deconstructed to de-link it to a system*; this also unlinks all other connected systems to that trigger, but has no effect on other triggers linked to the same system(s).

(* Or if the other end is deconstructed, the door, hatch, column, bridge or whatever, that un-links the trigger as well, but any other system remains linked.)

A lever is a device that can be linked to one or more other devices, permitting you to control these other devices through the lever's q menu. It needs one mechanism to be constructed (if you have a mechanism, you can build the lever with bTl). A lever is pulled through its q menu with aP. A nearby dwarf will then pull it.

Pressure plates are like levers, but are activated automatically by creatures stepping on it, or by fluids reaching a certain (pre-determined) depth.

Levers, when linked to objects, will never require more than two mechanisms, and will always be able to activate the linked objects across even the longest map with ease.

Levers normally have an "on" and an "off" state. Upon being pulled, everything they're connected to updates to the corresponding state, not just change state ("toggle"). This becomes important if you have several levers attached to the same device, which is permitted. Example: 2 levers are connected to a bridge. After pulling the first lever, the bridge will lift. A second lever will now only trigger an actual change when it is pulled twice (let down bridge). This in turn requires the first lever to be pulled twice to trigger a change (lift again), and so on.

"On" and "off" does not mean any random of the two possible lever states (like, depending on what state the lever was in when some device was linked up), but instead is fix:

• "dash to the right" (actually an acute accent) is on
• "dash to the left" (grave accent) is off

Note, however, that gear assemblies are an important exception to this: Instead of On/Off triggers, they indeed do toggle.

Several devices, such as floodgates and bridges, have a delayed response to all incoming signals, and will not respond to subsequent signals until the first has taken effect. For instance, if you pull a lever attached to a floodgate on then off in rapid succession, the floodgate will only respond to the first signal, independent of the position the lever rests in eventually.

Once a device is connected to a lever, it can only be unlinked by deconstructing the lever and reconstructing it. This will obviously require you to relink any other devices that you want to still be connected to this lever.

Objects that can be controlled by levers include:

Multiple Uses

• Bridge – Bridges have a delay of 100 steps when the lever is pulled.
  • On: Turns the bridge into either a raised drawbridge, or a retracted bridge, depending on which option was chosen when the the bridge was constructed.
  • Off: Returns the bridge to normal.

• Door – Note that once you connect a door, it is either completely open or locked. There is no "closed, but can be opened by a dwarf" state anymore.
  • On: Opens the door.
  • Off: Closes the door.

• Floodgate – After the lever is installed, it works exactly like a door. Floodgates, however, have a 100 tick delay. Therefore, it is more logical to use doors, at least until doors aren't usable for holding back water.
  • On: Opens the floodgate.
  • Off: Closes the floodgate.

• Hatch – When open it just disappears and allows water through. Note that, like doors, once you connect a hatch, it is either completely open or locked.
  • On: Opens the hatch.
  • Off: Closes the hatch.

• Grate – When it is open, it just disappears. Water goes through it just the same, but it cannot be walked on anymore. Anybody on it will fall.
  • On: Opens the grate.
  • Off: Closes the grate.

• Bars – When it is open, it just disappears. Water goes through it just the same, but it cannot be walked on anymore. Anybody on it will fall.
  • On: Opens the bars.
  • Off: Closes the bars.

• Upright Spear/Spikes
  • On: Retracts spears/spikes.
  • Off: Extends spears/spikes.

• Gear assembly – When it is disengaged, no power goes through it and anything that is being kept up by its presence (like a windmill right on top of it) falls down.
  • On: Toggles gear state.
  • Off: Toggles gear state.

One-Shot

• Cage – Deconstructs the cage and releases all of its contents. The cage and its attached mechanism will be left on the floor nearby; you recover the mechanism used on the cage but you do not recover the mechanism used in the lever. For this you need to deconstruct the lever too.

• Restraint – Deconstructs the chain/rope and releases whatever creature it held. The restraint's mechanism will be left on the floor nearby, and the restraint itself will remain attached to the creature's neck; again, you recover the mechanism used on the restraint but you do not recover the mechanism used in the lever. For this you need to deconstruct the lever too.
• Support – Deconstructs the support, ideally without a dwarf next to it. Most commonly used to cause controlled cave-ins.

Computing

Elaborate combinations of levers (or pressure plates) and other objects can be used to create mechanical systems that can perform various forms of computing.

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