Datasheet

1/20/2018 Resistors - learn.sparkfun.com
https://learn.sparkfun.com/tutorials/resistors?_ga=2.11435260.915074398.1516331036-531257354.1515063447 8/10
Here a resistor R and a photocell create a voltage divider to create a variable voltage output.
Pull-up Resistors
A pull-up resistor is used when you need to bias a microcontroller’s input pin to a known state. One end of the resistor is connected to the MCU’s pin, and the other end is
connected to a high voltage (usually 5V or 3.3V).
Without a pull-up resistor, inputs on the MCU could be left floating. There’s no guarantee that a floating pin is either high (5V) or low (0V).
Pull-up resistors are often used when interfacing with a button or switch input. The pull-up resistor can bias the input-pin when the switch is open. And it will protect the circuit
from a short when the switch is closed.
In the circuit above, when the switch is open the MCU’s input pin is connected through the resistor to 5V. When the switch closes, the input pin is connected directly to GND.
The value of a pull-up resistor doesn’t usually need to be anything specific. But it should be high enough that not too much power is lost if 5V or so is applied across it. Usually
values around 10kΩ work well.
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