# What are pull-up/pull-down resistors
- components used in electronic circuits
- ensure a digital input signal has a defined voltage level : 1(HIGH)/0(LOW)
- when no other active source influences the signal
- avoids disturbances, noise, mistakes, …
# Pin Input Circuit using a button or switch
How to connect a switch to a digital input pin?
prevent a floating input voltage
- no disturbances, noise, …
# External Resistors
physical components - not built in the microcontroller
# External Pull-down Resistor
connected between digital input & positive supply voltage (VCC/5V)
- puts voltage to LOW = 0
Button closed - HIGH input Button open - LOW input
# External Pull-up Resistor
connected between digital input & Ground (GND)
- puts voltage to HIGH = 1
Button closed - LOW input Button open - HIGH input
# Internal Resistor
Built into the microcontroller for digital IC Typically controlled through software settings
- not physical components
# Internal Pull-up Resistor
- ATmega has internal pull-up resistors
- Configuration with
- PORTx
- DDRx
Button closed: input is LOW Button open: input is HIGH