October 2021

Arduino microcontroller

The concept and application of "pull up" and "pull down" resistors

When using a microcontroller, when the pin we use as an input is not set to "HIGH" or "LOW" state, but its state "floats" between these two values, we say that it is in a state of high impedance. This is a condition that we definitely want to avoid because it leads to irregularities (unpredictability) in work and that is why we introduce a concept like"pull-up"and"pull-down"resistors. These are not special types of resistors, but resistors that allow us to maintain the desired state of the logic circuit regardless of the conditions. Arduino pin is connected via this resistor to a constant value, either to the + 5V power supply or to the GND (ground). In the first case it is a "pull-up", while in the second we are talking about a "pull-down" resistor.

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