Switches are literally everywhere! They are in many of the devices we use on a daily basis and a most basic part of just about every electronics project! So in this electronics basics tutorial we’re going to cover the different types of switches and what the applications that they are used for.
At its most basic, a switch turns something on or off. There’s a light switch for example in almost every room in your home. There is a switch to turn on or off your TV. There is even a switch to turn on and off your car or motorcycle! But switches are even more fundamental that turning your device on or off. What they actually do is close (allowing current to flow) or open a circuit (stopping the flow of current). This has many applications beyond the basic on/off function!
The buttons on your TV remote control that change the volume, channel, and inputs don’t turn on or off the remote or TV, but they do start or stop the flow of current, which tells the remote to do something by signalling an integrated circuit to transmit an IR code. In fact, we have a tutorial on building infrared circuits and a TV B-Gone remote!
Different Types of Switches
Different types of switches have different categories. There are two main categories of switches you’ll run into. They are mechanical switches and electrical switches. Mechanical switches require physical operation by a human, animal, or even a mechanical device. Electrical switches are switches that are controlled as part of a circuit, such as a relay or transistor. Electrical switches may or may not be solid state (i.e. semiconductor based).
Types of Mechanical Switches
Let’s cover the basic types of mechanical switches. While there are hundreds of types of mechanical switches in operation and production throughout the world, for brevity we’re going to focus in on the main types you are likely to encounter.
Poles vs Throws
Mechanical switches are usually described by a combination of two of their main characteristics: poles and throws.
- Poles: A pole refers to the number of circuits a switch can operate. A single-pole switch can only control a single circuit, while a double-pole switch can control two circuits. The limit to the number of poles is basically unlimited based on the construction methods of the switch. If you break it down to their very basics, a double-pole switch is nothing more than two separate single pole switches that are mechanically tied together.
- Throws: A throw refers to the number of output connections a switch can connect its input to. A simple single-throw switch is simply an on/off switch. When the switch is off current cannot flow. A double-throw switch connects the input to one of two output terminals. This might be used to switch between a red and green light for example. One or the other receives current, but not both at the same time.
Due to this, you’ll commonly see switches called by the number of poles and throws. Here are some common examples:
- SP-ST: Single-pole, single-throw
- DP-ST: Double-pole, single-throw
- DP-DT: Double-pole, double-throw
This illustration shows the difference between single-throw and double-throw (both single pole):
This illustration shows the difference between single-pole and double-pole (both single throw):
Pole and Throw Common Examples
Let’s take a look at some very common examples of these combinations of poles and throws as they apply to different types of switches. The most common are single and double. However, there are switches with many more poles and/or many more throws.
A single-pole single-throw (SPST) is the most common type of switch you will encounter. It simply controls current flow of a single input. On or off. Nothing more.
A double-pole single-throw (DPST) type of switch is much like an SPST switch, but it controls two inputs separately. This is very handy when you have two separate devices that need to be controlled by a single switch. In an arcade cabinet you might need to turn off the 5 volt powered Raspberry Pi and a 120 volt marquee backlight. A DPST switch allows you to control two devices with different voltages and current specifications.
A single-pole double-throw (SPDT) switch only controls a single input, but switches it between two outputs. This might allow you to switch between a red LED and and a green LED by flipping a switch. Neither receive power at the same time. A SPDT switch can replace a SPST switch by only connecting one of the two outputs.
There are of course many more combinations of the poles and throws. Here’s a handy illustration of some of the most common types:
Momentary vs. Latching Switches
As we continue to explore the different types of switches, another important distinction in switches you’ll encounter is the bias. Some switches maintain the state you set them in, until you physically change the state, this is called a latching switch (sometimes referred to as a maintained switch). A momentary switch on the other hand will only maintain its state while you are pressing it and return to its normal state when you release it. Momentary switches are generally activated by pressure (i.e. pushing the button on your arcade game), however, they could be activated by other means such as temperature, or light.
Types of Electrical Switches
Now let’s go over the types of electrical switches. As we mentioned earlier, electrical switches are controlled by an electric change. They can be either electro-mechanical in design, or semiconductor based.
Relays are electro-mechanical types of switches. They usually consist of a coil that generates a magnetic charge when current travels through it. This magnetic charge either attracts or repels fixed type magnet that is connected to a mechanical switch. Relays are perfect for allowing low voltage devices to control high voltage circuits. For example, a 5 volt GPIO pin from an Arduino or Raspberry Pi can control a 120 volt lamp using a relay.
Of course, depending on the type of relay, it could be any combination of high-low/voltage-current! It could be 240 volts AC activating an LED!
RELATED: Arduino Relay Tutorial
Some people spend years tinkering with electronics before it dawns on them that a transistor is (or can be) an electrical switch! Transistors have three leads that are known as the base, collector, and emitter. We’ll skip the complexity of transistors for the purposes of this tutorial, but suffice it to say that the saturation level of the transistor is reached, it will act as a simple electrical switch.
Other Electrical Switches
Of course there many other types of electrical components that can be an electrical switch. Such as thyristors, silicon controlled rectifiers, and MOSFETs. Even a diode is a type of electrical switch when you think about it. When it is restricting current in its reverse direction it is acting as a switch!
If you have any questions, leave a comment below and we’ll do our best to help you out!