Pull-Down Pull-Up Resistor
Fleeting- External reference: https://electronics.stackexchange.com/questions/481332/what-does-pull-up-resistor-and-pull-down-resistor-mean-how-do-i-implement-them
- External reference: https://forum.allaboutcircuits.com/threads/what-happens-if-an-input-has-neither-a-pull-up-nor-a-pull-down-resistor.193057/
pull-down pull-up resistor
pull-up/pull-down resistor is used when a pin may not need to be used, so the resistor establishes a default value with no other input
logic signal can be supplied from a passive source such as a pull-up or pull-down resistor
If a digital input is going to be actively driven at all times, then no pull-up or pull-down resistor is needed
A pull-up resistor pulls the voltage up to the “high” logical level (5V, 3.3V or whatever is used as a “high” level) when the is no signal driving the input.
A pull-down resistor pulls the voltage down to the “low” logical level (0V or close to it) when the is no signal driving the input.
achieved because the input impedance of the device being pulled up/down is usually very high (and much higher than the resistor itself, so they won’t form a voltage divider).
pull-up or a pull-down resistor, when connected to a point in a circuit, provides that point with a weak default voltage which dominates unless some other stronger component forces it to something else.
In other words, saying that an input is floating means that when it’s not connected to anything, and thus it can gather random charge which has nowhere to escape. This might trigger a false reading. When the input is pulled down, the charge will always escape (through the pull-down resistor).
— https://www.reddit.com/r/arduino/comments/rr8gw0/what_is_the_point_of_a_pulldown_resistor/