This article explains what are switches in electronics and how they work.
Switches are very simple components essential in your electronics circuits. A switch can:
- act as an interrupter, interrupting the electric current. In the example in the figure below, the switch is either interrupting the current to flow and the LED doesn’t turn on, or it allows the electric flow and the LED turns on.
- act as a diverter, driving the current to other part of the circuit. In the example in the figure below, if the switch is turned to one side, one LED turns on and the other turns off, and vice-versa.
There are a wide variety of switches to fulfill your needs, for example, switch two things at the same time, switch two things alternately, switch something when the button is pressed, and so on.
Types of Switches
You can find push-button, toggle, rotary and magnetic reed switches. Although there are other types, these are the most common. I’m sure that if you search on the internet you’ll find different ones.
Pushbuttons come in a wide variety of shapes and forms.
There are two types of pushbuttons:
- normally open (NO) – When the pushbutton is in its normal state (not pressed), the current doesn’t flow. When you press the pushbutton, you allow the current to flow.
- normally closed (NC) – It works the other way around.When the pushbutton is in its normal state (pressed), the current flows. When you press the pushbutton, you open the circuit and the current doesn’t flow.
In a toggle switch you have a lever that you turn to one side or to the other to make the current flow to one side or to other, or to not flow at all.
There are several types of toggle switches. These are characterized by the pole and the throw. A pole represents a contact. The pole represents the connections that your pole can do. You’ll understand this better with the examples below.
For describing a switch, the following format is used:
- “P” for pole;
- “T” for throw;
- “S” for single;
- “D” for double;
Single Pole Single Throw (SPST) toggle switch
The metal contact part makes the connection between the two pins. When the metal contact is at the left, there is no connection between the pins. When it is at the right the two pins are connected, and the current flows from one pin to the other.
Single Pole Double Throw (SPDT) toggle switch
When the metal contact part is turned to the left, there’s contact between pin a and pin b. When the metal contact part is turned to the right, the current flows through a and c.
Double pole single throw (DPST) toggle switch
In a DPST toggle switch, you have two poles. These are either both turned on or both turned off. Each pole can make just one connection, that’s why these switch is single throw.
Double pole double throw (DPDT) toggle switch
In this kind of switch, you have two poles, and each of them can make two different connections.
(n)P(m)T toggle switches
Besides the examples presented, there are also toggle switches of multiple (n) poles and multiple (m) throws.
Rotary switches have several positions, and you have to rotate the knob to select the position. Here’s an example of a rotary switch with 3 positions:
There are rotary switches with other numbers of positions, for example, 4, 6 and 16.
Here’s a simple figure to understand how these kind of buttons work:
Rotating the switch will select a different connection.
Magnetic Reed Switches
Magnetic reed switches are closed or opened depending on the magnetic field near them. Take a look at the picture below:
The electrical circuit is closed when a magnet is near the switch (less than 13 mm (0.5’’) away). When the magnet is far away from the switch, the circuit is opened.
I hope you’ve learn something new today and you’ve found this post useful.
If you’d like to know more about electronics basics or if you’d like to start into the world of electronics make sure you check out our Electronics for Beginners eBook.
Thanks for reading.