On the Arduino Due, it is between 50kΩ and 150kΩ. On most AVR-based boards, the value is guaranteed to be between 20kΩ and 50kΩ. The value of this pullup depends on the microcontroller used. This effectively inverts the behavior of the INPUT mode, where HIGH means the sensor is off, and LOW means the sensor is on. These built-in pullup resistors are accessed by setting the pinMode() as INPUT_PULLUP. There are 20K pullup resistors built into the Atmega chip that can be accessed from software. Properties of Pins Configured as INPUT_PULLUP A 10K resistor is a good value for a pullup or pulldown resistor. This can be done by adding a pullup resistor (to +5V), or a pulldown resistor (resistor to ground) on the input. Often it is useful to steer an input pin to a known state if no input is present. Pullup Resistors with pins configured as INPUT This also means however, that pins configured as pinMode(pin, INPUT) with nothing connected to them, or with wires connected to them that are not connected to other circuits, will report seemingly random changes in pin state, picking up electrical noise from the environment, or capacitively coupling the state of a nearby pin. This means that it takes very little current to move the input pin from one state to another, and can make the pins useful for such tasks as implementing a capacitive touch sensor, reading an LED as a photodiode, or reading an analog sensor with a scheme such as RCTime.
#Arduino uno nano equivalent pins series
Input pins make extremely small demands on the circuit that they are sampling, equivalent to a series resistor of 100 megohm in front of the pin. Pins configured this way are said to be in a high-impedance state. While the title of this document refers to digital pins, it is important to note that vast majority of Arduino (Atmega) analog pins, may be configured, and used, in exactly the same manner as digital pins.Īrduino (Atmega) pins default to inputs, so they don't need to be explicitly declared as inputs with pinMode() when you're using them as inputs. This document explains the functioning of the pins in those modes. The pins on the Arduino can be configured as either inputs or outputs.