The switches used in each cockpit can be of different types, even in one particular cockpit there can be various switch combinations - simple toggle switches with two fixed ON-OFF states, toggle switches with 3 ON-OFF-ON positions, rocker switches, pushbutton switches with alternate (fixed) or momentary action.
Before you start building your home cockpit, you should do some homework - learn all about the systems and controls in the plane cockpit you want to build, clarify what type of switches you will need to have in your cockpit. Sometimes, for example, you may think you should use a momentary pushbutton to switch something on your overhead panel, but in reality it may turn out to be an alternate pushbutton swich with fixed states.
- Actuator - The outer part of the switch, which is moved by an external force (hand / finger) to operate the switch
- Terminals - The switch output/input leads to wiring/solderind.
- Every switch has two types of signal terminals - "Pole" and "Throw", at least one of each (SPST type). A switch is classified by the number of throws and poles.
- The poles are the "input" terminals and define how many independent circuits the switch can control.
- The throws are the output terminals and define the number of switchable output than can be connected to one pole input.
- Alternate/maintained switches can be OFF or ON, momentary switches return into normal position after you release their actuator.
The simplest toggle switch has only two terminals - one "Pole" and one "Throw", this is the SPST toggle switch type that has two fixed (maintained OFF-ON) states. There is no difference between pole and throw for such switch in terms of electrical connection (you can connect it either way).
Very commonly used toggle switches have only 3 terminals - one "Pole" and two "Throw", this is the SPDT toggle switch type that also has two fixed states but connects one input circuit (pole) to one of two output circuits. No matter if you use only one output circuit or both, you need to know where the pole terminal is located.
A 3-position toggle switch that also has 3 terminals is the same as SPDT switch but it has one more fixed position in the center (OFF). It can be called a Single pole, centre off (SPCO) switch. So, it has 3 fixed positions (ON-OFF-ON) and is used like two separate switches that aren't supposed to be ON at the same time.
For example, a 3-position starter switch in King Air has two maintained positions (center OFF and upper mechanically locked ON) and one lower momentary "STARTER ONLY" position that is spring-loaded to OFF position.
A simple momentary pushbutton has two signal terminals (SPST type). Actually, there is no difference between them in terms of electrical connection. The push-button type can be either normally-open or normally-closed.
Momentary pushbutton switch remains in its operated position only while it is being actuated and held:
- when you press the button actuator, the shorting contact moves to the operated position.
- when you release an actuator, the shorting contact returns to it's normal position.
In its normal position (when the button is not actuated) the contacts inside of the pushbutton can be either open-circuit or short-circuit - these are so called "normally-open" (NO) or "normally-closed" (NC) pushbutton types.
This single pole, double throw (SPDT) momentary pushbutton switch has both types of contact (NO and NC), also called a changeover switch. It remains in its operated position only while it is being actuated and held:
- when you press the button actuator, the pole-contact is shorting throw-contact #1 in operated position.
- when you release the actuator, the pole-contact is shorting throw-contact #2 in normal position.
Alternate push-button switch has an actuator locking mechanism to maintain it in operated position after releasing the button.- when you press the button actuator once, the internal circuit shorts the contacts and remains in that position when you release the actuator (the operating state is maintained).
There are two types of alternate push-button switches: one in which the actuator (button) returns to its original position every time it is released (both in closed or open position of the contacts), and another in which the actuator remains locked in a depressed state (like in the picture on left).
There are many such alternate pushbutton switches on the market, including "Korry-type" switches that are often used in overhead panels. Some of them can be too expensive for a home cockpit, especially those with LED option, but you can find enough cheap push-buttons on AliExpress or Ebay and make backlit cover caps by yourself.For example - Cheap Latching Push Button Switch ($0.4 a piece)