Common question that comes up about pull-up resistors: what value do you pick and why not just use a piece of wire? In this follow-up electronics tutorial, the bald engineer looks at how to pick a pull-up resistor value. Note that while focused on pull-up everything said in this video would apply to pull-down as well.
If you’re new to pull-up resistors, check out this longer Pull-Up Resistor Tutorial.Watch the full video
With ultra-low-power designs powered by small batteries becoming more popular, “calculating” pull-ups can become much more necessary than it ever used to be. In this Quora answer I describe the basics of looking at input leakage currents, at worse-case, as a means of optimising power consumption while staying well within logic thresholds:
Hi James, as always very informative video. I have one question; Why or when should the internal pull-up resister in the arduino uno be used or should we always add in a pull up resister? for example (pinMode(2,INPUT_PULLUP);)
No, you should not always use them. Push buttons are the most common use. You also use them when devices use “open collector” outputs. A PIR motion sensor, for example. I2C devices use pull-up resistors since SDA and SCL are open-collector drivers.