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Buttons and switches 101

May 18, 2019 tutorial

Whenever a circuit relies on an external mechanical input we use switches or buttons. I thought it would be interesting to collect the most common variants of switches and buttons that are typically found in electronics. Please let me know if I missed your favorite one!

Buttons & switches... What is out there?

First off, there is a difference between a button and a switch. A button creates a temporary connection, whereas a switch creates a permanent connection.

Any switch can be classified by how many poles and throws it has. The number poles describes the amount of electrically disconnected switches contained in a certain switch. By flipping one lever, for example, you could actually actuate two distinct electrical connections. This switch then has two poles. The term throw refers to the amount of of positions the switch can be in.

If that sounds confusing to you, don't worry! We will go through a lot of examples below, and we will list the number of poles and throws for each of the switches!

A word on electrical characteristics

Before jumping into the examples below, I want to mention two important parameters when it comes to buttons and switches. The maximum voltage and current that can be controlled. Some switches are designed for switching the line voltage (which can be 110V or 220V, depending on where you live in the world). Other switches, however, are only designed for small voltages of 12V or so. These are only intended for switching small loads. In the context of hobby electronics we can mostly use any switch we want, because all we do is switch 5V or 12V.

If you consider to switch an actual load, it is important to know how much current you will be switching, too! The product of the voltage V and the current I then gives the total power that your switch has to conduct, P = V × I.

If you are not sure, check the datasheet of your switch, or ask somebody on the internet.

Pushbuttons

Pushbuttons are probably the most common switches in electronic circuits that we talk about here.

Standard Pushbutton

One pole, one throw, 24V, 500mA.

This one is useful for chassis mount.

Tactile Switch

One pole, one throw, 12V, 50mA.

This type is can be plugged directly into breadboards or soldered into PCBs.

Switches

Switches create permanent connections. Here are some varieties:

Power Switch

2 poles, 1 throw, 125V AC, 20A.

Used to switch on substantial electric loads (machines, equipment).

Toggle Switch

1 pole, 2 throws, 120V AC, 5A.

Used to toggle a connection. Can be used for smaller loads as well.

Toggle Switch

1 pole, 2 throws, 120V AC, 5A. This switch also has a neutral position in the middle, when there is no connection from the center pin to the outside pins.

Same as the toggle switch above, but with a neutral position in the middle.

Almost a Toggle Switch

1 pole, 1 throw, 120V AC, 10A.

Looks like a toggle switch, but is actually just a regular switch with one throw.

DIP Switch

7 poles, 1 throw, 24V, 25mA.

DIP stands for “Dual In-line Pin” and these switches are used primarily to configure logic circuits. They should not be used for heavy loads.

Slide Switch

1 pole, 2 throws, 125V, 5A.

These are very common on battery-operated hand-held devices, but they can also switch medium electric loads.

Rotary Switches

Rotary switches are just like a regular switch, but with more poles and throws. They can be quite versatile, but they can only switch small electric loads.

Rotary Switch 12 positions, 1 pole

1 pole, 12 throws, 250V, 150mA.

Rotary Switch 6 positions, 2 poles

2 poles, 6 throws, 250V, 150mA.

Rotary Switch 3 positions, 4 poles

4 poles, 3 throws, 250V, 150mA.

Rotary Encoders

Rotary encoders are quite similar to rotary switches, but more than just one throw can be active at a time.

These encoders typically have a dial that can be turned into 10 (BCD) or 16 (hexadecimal) positions, much like a rotary switch. Depending on where the dial is pointing, the input pole of the switch (in the below it is called “C”) is connected to various outputs.

For example: say the switch is set to position 7. Then, the pins1, 2, and 4 will be connected with C (because 7 is the sum of 1, 2, and 4).

These encoders are useful if you want to send an option to, say, a microcontroller (for example, a number between 1 and 16), but you don't want to waste 16 pins of the microcontroller. Note that these encoders can only switch very small loads.

Rotary BCD DIP Switch

1 pole, 4 throws, 25V, 25mA.

Rotary Hex DIP Switch

1 pole, 4 throws, 25V, 25mA.

Miscellaneous

This is the fun part. Let me know if I missed your favorite odd-ball switch or button!

Reed switch

1 pole, 2 throws, 125V AC, 100mA.

This is a switch that is activated by the presence of a magnet. The thin “reed” is made of paramagnetic, conducting material that switches position when a magnetic field is close by.

Reed switches can switch only small loads.

Relay

1 pole, 2 throws, 125V AC, 10A.

A relay is just like a reed switch, but the magnet is replaced by an electromagnet. The electromagnet typically needs anything between 5-12V DC to run, but the load can be quite large.

Key switch

1 pole, 1 throw, 125V AC, 10A.

This is just a simple switch, but it is activated by a key.

Limit Switch

1 pole, 1 throw, 125V, 10A.

A limit switch is used in mechanical applications. Typically, its arm is mechanically activated when a piece of the apparatus has reached a critical limiting point where it is supposed to stop moving.

Vibration Switch

1 pole, 1 throw, 12V, 20mA.

When you shake this switch, the spring eventually touches the internal rod and closes the circuit momentarily.

Final thoughts

There are many other interesting switches and buttons out there that I probably forgot to mention. The ones I listed here are rather common (perhaps with the exception of some in the “Miscellaneous” section) and should give you a good first idea of what is out there.

Next week we will learn how to connect a simple switch to a microcontroller and read out its status! Stay tuned!

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Tag Cloud

  • pushbutton
  • switch
  • tactile switch
  • toggle switch
  • DIP switch
  • slide switch
  • limit switch
  • rotary switch
  • rotary BCD DIP switch
  • rotary hex DIP switch
  • reed switch
  • relay