Arduino Projects   |   Raspberry Pi   |   Electronic Circuits   |   AVR   |   PIC   |   8051   |   Electronic Projects

Insight - How Toggle Switch works

Written By: 

Arpit Jain


SPDT stands for Single Pole Double Throw. It comes with 6 pin. It has 2 states ON and ON. For instance if we have two devices a red LED and a blue LED then SPDT switch will turn ON red in one position and blue in other position. By making different connections of the pins the two ON states can be made of same polarity or opposite polarity. Hence, it will switch ON a different device in each position. Hence, it is also known as changeover switch. This switch has found applications in industry, etc.
6-Pin SPDT Switch
Fig. 1: 6-Pin SPDT Switch
It’s the symbol to represent a SPDT switch.
Let’s take closer look into SPDT switch and see its working. The switch was enclosed in a protective case which is shown below.

Internal Structure

Protective Case That Encloses SPDT Switch
Fig. 2: Protective Case That Encloses SPDT Switch
There are 8 pins in SPDT switch. These pins are engraved in a plastic board. These pins engraved in the board are show in the image shown below.
Image Showing Pins Engraved in Board
Fig. 3: Image Showing Pins Engraved in Board
Each of the 8 pins is engraved inside the board. These pins are beaten on top and are flattened. Over those flatten edges two metallic plates are kept. When the handle of the switch is moved then these plates make contact of the pins. Due to these different contact positions the SPDT switch performs its function.

Center Pins Arrangement

Image Showing Layout and Shape of Pins
Fig. 4: Image Showing Layout and Shape of Pins
 In the image of the switch it is seen that the middle pin is different in structure. Actually these pins and the plates are made like this so that plate can lie over them as inclined plane. Hence, when the handle is in one position there is contact between the middle pin and its adjacent pin. And in other position the middle pins are in contact with other pin. The image of the pins is shown below.
Fig. 5: Pins
For making the contacts between the pins a structure is used which is shown below.


SPDT Switch Handle
Fig. 6: SPDT Switch Handle
The handle of the switch is actually hollow from inside and contains a spring. This spring pushes the above shown structure. Hence, the switch stays in the same position until unless changed.

Handle Spring

Handle Spring
Fig. 7: Handle Spring


the topic can bbe more informative and helpful if the connections to the pins are told and how the connections changes when we change the position of changer in switch istold..