What is a good pullup/down resistor value?

That's where experience and experimentation come in. Here are some rules of thumb when guessing at a good pullup/down resistor value: For most things, 3.3k to 10k ohms works just fine. For power sensitive circuits, use a higher value. 50k or even 100k ohms can work for many applications (but not all).

What are pull up and pull down resistors?

Pull-up and pull-down resistors are essential components in digital circuits that establish a defined logic state (high or low) when the input is in a high-impedance state. The main difference between pull up and pull down resistor is their connection and default logic state:

How do I choose a pull-up resistor?

Rule of thumb The rule of thumb when choosing a pull-up resistor is to choose a resistance value that is at least 10 times smaller than the input impedance (or the internal resistance) of the pin. Often, a pull-up value of 10 kΩ will do the trick.

When do you need a pull-up resistor?

You need to use a pull-up resistor when you have a low default impedance state and wish to pull the signal to ‘high’. In the figure above, a pull-up resistor with a fixed value was used to connect the voltage supply and a particular pin in the digital logic circuit.

How to choose a pull-down resistor?

Because significant resistance creates more voltage drop, it results in gate input voltage beyond the normal low voltage range. Hence, choose a pull-down resistor at a voltage drop of 0.4-0.5 V. Then select the pull-down resistance value below its maximum value.

How much voltage does a 1 a pullup Accross a resistor?

If you were to use a 1 MΩ pullup, for example, then that 1 µA would cause 1 Volt accross the 1 MΩ resistor. Let's say this is a 5V system, so that means the pin is only guaranteed to be up to 4V. Now you have to look at the digital input spec and see what the minimum voltage requirement is for a logic high level.