Sensors: PushButtons and Switches

Buttons are the simplest group of discrete sensors. They act as a valve, opening or closing the flow of electrons through a branch of your circuit.

Buttons can be interfaced directly to a microcontroller's digital input requiring only a pull-up resistor.

Button nomenclature:

• SPDT - Single Pole, Double Throw. Has three contacts, signal of interest would normally go in the middle and is connected to one of the two other contact depending on the switch position.
• DPDT - Double Pole, Double Throw. Has the same structure as the SPST but with a second set of contact so two signal can be switched together.
• Normally Open - The contacts are connected only while the button is actuated. aka. Momentary Contact
• Normally Closed - The contacts are connected except while the button is actuated.
• Toggle - Toggles between closed and open with each actuation
  
  There are many other types of switches, mechanical, electrical (transistors, photo-transistors ...), and combinations of the two (solenoids ...).