Electrical Lab - how a 4-pin momentary tactile switch works



UpdatedUpdatedJune 12 - 2017June 12 - 2017

Momentary tactile switch (normally open) pin configuration

tactile-switch



A tactile switch may have 4, 6, 8 or even more pins. Here we will discuss about a simple tactile switch which has 4 pins.

We will use jumper wires to build our own tactile switch from scratch. Then it will become clear to us how a normal tactile switch works and how we can use it as a pushbutton.

Let's first take two jumper wires (red and yellow) and place them on a breadboard to create our 4-pin tactile switch which basically has 2 terminals.
tactile-switch-how-it-works-1



So normally when we don't press the button, it looks just like the above image. When we press the button, then terminal 1 + terminal 2 become short (in image green wires are used to denote short circuit).
tactile-switch-how-it-works-2



Now Connect terminal 1 VCC (+5V).
Terminal 2 10K resistor GND (ground).
LED anode (+ve) terminal 2.
LED cathode (-ve) 220 Ohm resistor GND (ground).
The green wires are not connected which means the tactile switch is not pressed and LED is OFF.
tactile-switch-how-it-works-3



The green wires are connected which means the tactile switch is pressed and LED is ON.
tactile-switch-how-it-works-4



Summary
When the button is not pressed, the circuit is incomplete so current does not flow from VCC (+5V).
When the button is pressed, current flows from terminal 1 (VCC) to terminal 2. Since we have a very high resistance (10K) between terminal 2 and ground, current flows through the LED.


Simulation:
External link

Hint: Click on Start Simulation, then activate LED by pressing the tactile switch. When you release the switch or button, LED will be deactivated.



For a normally closed momentary tactile switch, it works in the opposite way. So by default terminal 1 and 2 are connected. When the button is pressed, the terminals become open so no current flows.