The Genesis and Machines campaigns show the basics of how to use Metal to carry Electros and power circuits. However, there's so many subtle yet awesome things that you can do with circuits in this game, some of which only depend on how you arrange the metal. To encourage more complex level design (and maybe teach you something you may not already know), I've decided to start this thread to compile tips and tricks regarding circuit design.

I'll start off with basic stuff: circuit components that are just Metal and some insulating material (I used Wall, but anything that doesn't fall and doesn't conduct Electros will work).

DIODE

A diode is a component that carries current only one direction through a wire. Here, Electros can flow from the input to the output just fine, but they CANNOT flow from the output to the input (they cancel out at the top of the diode).

AIR GAP

Because exposed metal will cast out Electros, you can use a gap of air as part of your circuit design as long as it is vertical as in the picture. This does two things: (1) Electros can pass freely from the top to the bottom, but not the other way (much like the diode above), and (2) any Electros coming from the bottom will reverse and go back out the bottom (this is different from the diode, where the Electros simply stop when they hit it).

AIR GAP JOINT

Normally, if you try to join two inputs together to feed one output, the Electros will split, and you'll have Electros going out the inputs as well. You can fix this with diodes, but we can also use an air gap to join multiple inputs together as shown above. The gap isolates the two inputs so that Electros on one will not affect the other. This is useful for making loops (for an example, check out my level "Hurry!", which uses a giant one of these to create a four-minute timer).

Amplifier

We can use the fact that air gaps can reverse Electros to our advantage. In this "Amplifier", a single Electro coming through the input hits the metal U-shape in the middle and bounces back and forth between the two air gaps. Every time the Electro passes through the crook of the U-shape, it splits and sends an Electro through the output. The end result is a stream of Electros out of the output. The timing can be adjusted by lengthening and shortening the legs of the U-shape, and the amplifier can even be toggled on and off by sending another Electro into the input (a second Electro will cancel the first one). For an example, check out my level "Melt the Ice" that uses an amplifier to control the flow of Acid through the pipes.

Finally, I'll pull all of these together into one mega-device that can be quite handy:

RESETTABLE FUSE

It looks complicated, and it is a little, but all it does is combine the components I've already discussed to do something neat. The point of this device is to allow through only one Electro at a time until it is reset, kind of like the E.Fuse element except that it is reusable. The best way to explain this one is to show what happens when you hit each switch.

When you send an Electro through the input, it flows through the air gap and splits at the junction. One Electro goes up to activate the E.Multi, which fills the air gap with the Gas element; this prevents more Electros from passing through the gap. The other Electro goes down through the diode to the output, which in this case is just connected to an LED. At this point, hitting the left switch will no longer light up the LED.

To reset the fuse, send an Electro through the Reset line using the right switch. The Electro passes through the diode and splits at the junction. One goes along the left path straight to the E.Drain, which toggles it on and removes the Gas from the gap. The other Electro goes along the right path and hits the air gap, reversing its course. When this second Electro hits the junction, it will again split, sending one to the E.Drain to toggle it back off, and sending the other to the wrong side of the diode which eliminates it. When everything is done, the fuse will be back in its initial state.

If that explanation was too confusing, I put together a short demo named "Resettable Fuse" that puts one of these into an Avatar level so that you can play around with it and see everything working in real time.

Time for more circuits! This time, I'll focus on one particular device that has turned out to be extremely useful after playing around with it in the editor for a little while.

TRANSMISSION GATE

If you read my previous post, this will probably look very familiar. A transmission gate is a mashup between a diode and the fuse I described earlier. This device has two states: the "Off" state, the default state where the air gap is empty, and the "On" state, where the air gap has been filled with Gas by sending an Electro through the Gate input to the E.Multi.

In the Off state, both sides of the transmission gate can conduct Electros, but because the bottom of the device emulates the input of a diode, any Electros that try to pass from the input to the output will cancel out. As the name implies, no Electros can go through the transmission gate in the Off state.

In the On state, only the right side can conduct Electros due to the Gas blocking the left path. Because the left side can't cancel the right side out anymore, this single Electro CAN go through the transmission gate unimpeded, providing a clear path from input to output.

The transmission gate is essentially a digital switch, which means we can daisy-chain them together in various ways to set up logic circuits. For example:

AND GATE

Cascading two or more transmission gates in series as in the picture above means that there is only a clear path from input to output if both Gate inputs have been triggered (i.e. GateA AND GateB).

OR GATE

Cascading two or more transmission gates in parallel as in the picture above means that there is a clear path from input to output if either Gate input has been triggered (i.e. GateA OR GateB). Remember to use diodes or an air gap to isolate the two transmission gate outputs from each other!

NOT GATE

This is a bit of a twist on the transmission gate. In the NOT gate, the air gap starts with Gas inside it, and triggering the Gate input activates the E.Drain to remove the Gas. It's the reverse of the regular transmission gate, which goes from Off to On. This gate goes from On to Off!

So how is all of this useful for level design? Well, if you want to see an example, I recently put together a ninja level called "Enlightenment" that uses a four-input AND gate to drive the E.Gate that leads to the exit. The player must hit all four switches in the level to be able to get to the lotus. The beautiful part is that it doesn't matter what order the player hits the switches, adding a touch of non-linear exploration to the level.

Pictured above is the AND gate. The input is connected to a slow Battery that constantly feeds Electros through the input of the AND gate as far as it can. Once all four Gate inputs have been triggered, the Electros from the Battery can pass all the way through to the E.Fuse, an amplifier, and finally open the E.Gate.

The four Gate inputs are tied to four colored pedestals like the one above that are scattered around the level. Each pedestal consists of a Human Sensor to generate the Electro, a fuse (to prevent the player from accidentally hitting it twice), an amplifier to multiply the Electro, and some LEDs. The pedestal switch ultimately does two things: (1) sends a stream of Electros to the "torch" on the wall which is basically just Bulbs and E.Multis that spit out fire, and (2) sends a single Electro to one of the four Gate inputs to trigger it.

That's it for now. Hopefully these ideas will help you design amazing levels of your own!