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:
Keep on Soldering!