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Question from reader: Pull-up resistor

July 6, 2015 By Øyvind Nydal Dahl Leave a Comment

Microcontroller tutorial: Atmega32 in a circuitQUESTION: I am unable to understand Pull Up and Pull Down resistor. why and when to use this.. Can you please help me..

OYVIND: Pull-up and pull-down resistors are used for example on digital inputs on a microcontroller. They make sure you have either a valid 1 or 0 at the input, when nothing else is connected.

A pull-up resistor is connected from the input and up to the positive power supply. It pulls the input up to a 1, when nothing else is connected.

A pull-down resistor is connected from the input and down to ground. It pulls the input down to 0, when nothing else is connected.

A guide to the 1’s and 0’s that enables everything from computers to smart phones, is included in both the “Curious Beginner” and the “Dedicated Learner” packages with my eBook “Getting Started With Electronics”.

Learn more about the eBook and guide here:
https://www.build-electronic-circuits.com/products/ebook-2nd-edition

Keep on Soldering!
Oyvind

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