I would guess that a pull down resistor would be the same except going to ground, and would be used when the input signal was a positive voltage. Basically just swapping the switch and the resistor.

depends on what state u desire, if you want high state, use pullup..... low state, use pulldown...

adding to the above, it's much easier to find a ground plane on the circuit board than a logic level line.

Nah he should explain that with the different potentials

Pull up means the high state is the default one with the switch open. Pressing the switch transitions to a low state. Pull down means the low state is the default one with the switch open. Pressing the switch transitions to a high state.

You can just use INPUT_PULLUP pin mode. Then internally, 10-50 kOhm pullup resistor is applied to the pin. Keep in mind that breadboards are evil and are out to hurt your feelings.

@@SianaGearz That breadboard fact has helped me sleep more peacefully. Thank you. 😁

I’m just getting them a year later but every single one has been amazing so far. Great refresh/review

In Arduino IDE it can be configured easily with setting the pin as Pull-up Input

Knowing that they exist is the first step to understanding there are internal ones

Not all microcontrollers have internal pull-up or pull-down support. And the internal value is normally mugh higher than 1k because a 1k pull-up adds significantly to the current consumption. Geounding 3V3 over a 1k resistor means 3.3 mA current. And that is over 10 mW power lost.

It is a very wimpy low current pullup though, which can sometimes be unstable. It is actually a feature on any fully featured microcontroller, including AVR 8-bit and PIC and whatever else pretty much you can think of. ARM micros have pretty much the wimpiest pull-ups though.

Note that "ARM" is a processor core. The different chip manufacturers will then glue on I/O functionality. Not all ARM chips are even microcontrollers. So it makes a difference if using a STM32 or a NXP 17xx microcontroller.

You don't always need a transistor. It depends on whether the output pin of the microcontroller can sink or source enough current to drive the load connected to it. So check the current sink and source capability of the output pin.

Yep!

Yes, but because of the high resistance, it’s minuscule, not enough to matter. It’s flowing just enough to register. P = V^2 / R. if this were 3.3v, then 3.3*3.3/10,000 = 0.001 watts. With 5v, 0.0025 watts. Tiny

Yep!

Well done sir

Normally you decide what *idle* state you want. But if using a switch, it matters if using a make or break switch.

@@perwestermark8920 thank you, but still am not getting the reason to use exactly why?

@@studiovlog3635 Many (most) times you can do either choice. But sometimes someone else is responsible for the part containing a switch. If they say "this car has a switch that shorts to ground when trigged" then you must look into the opposite - i.e. pull sig al high when the switch isn't closed. If someone say "this signal/switch will supply 3V3 when trigged" (and we are assuming your processor supports 3V3 for your input pins) then you must supply opposite. I.e. pull the pin low when the switch is not active. If someone says "this signal is 3V3 or 0V" then you can use it directly. But what happens if the cable is ripped off? If 3V3 in means a request to run a motor and you don't want the motor to run if the cable is broken then you select a pull down. If 0V means a request to run the motor and you do not want the motor run if cable is broken then you add a pull up. This means you must select pull up or pull down when someone else have already decided what the input looks like. In a situation where you decide, then you can use pull uo and switch to ground. Or pull down and switch to VCC.

@@perwestermark8920 thank you , I actually did some trials few years back to understand this, and since I did it only few times I forgot, but yup now I remember and understood a more better than what I had self taught myself, your explanation was very clean and direct on point. Thank you..

it's not critical, you'll sometimes hear this referred to as "Jellybean" components, ones that are so generic that they can be used for basically anything. For the purpose of this video, it wouldn't matter if you used 1K Ohm, 10K Ohm, even 100K Ohm would be fine. When you start getting into the weeds and doing specialized things, then you'll have to worry about it more... for example maybe you wouldn't use 1K ohm for a pull-up if you expect the button to be pressed down 90% of the time, and you need to run it off a small battery. The very tiny power loss through the resistor and button would be 10x lower if you used a 10K resistor, or 100x better for 100K etc. Maybe you're in an industrial or other high-stakes environment where interference is critical to filter out, in that case the simple pull-up resistor may not be enough, but at very least you would want a low value so the "launch the missles button" never gets falsely pressed, power consumption be damned haha

@@PilotPlater to clarify a bit more. the lower your value the higher your current draw when the button is pressed, the higher the value the lower the voltage reads in the unpressed case. The second part is because you're creating a voltage divider between the input impedance (can just be thought of as resistance in DC) [which iirc is often 1M+ for micro inputs] and your pull-up resistor

@@psynautic and it's not about just free standing voltage when the button is not pressed, but noise interference. Ultimately it'll probably never matter in non-industrial settings

Anything between 1k and 10k should work fine

The power is only wasted here when the button is pressed anyway! Depending on sort of battery and pullup strength, the drain can be substantial though, you should calculate it, especially if you use NC (normally closed) connected switches anywhere.

If you have a long cable working as an antenna to pick up noise, then you need a lower resistance to strongly hold the wire. If your signal traces are short and not picking up noise, then you can select a much larger resistance and keep down the current. In some situations, a processor pin held high can be used with the pull up resistor instead of Vcc. This means the program can turn on/off the pull up voltage so it's only when the switch state is checked by the code that there is any 3V3 pull-up. This obviously means the code needs to regularly poll the switch state.

This method is for inputs where the button pressed time is much shorter than the intended lifetime of the battery. And the relatively high value of the resistor leads to a negible battery drain anyway.

@@Hauketal really helpful, thank you

You can normally use a quite big resistor unless you have a very noisy environment. With 3V3 a 1k resistor would be 3.3 mA. 10k would ve 0.33 mA. 47k would be 70 uA. Also, a switch can be from pin to ground or from pin to Vcc. Which means you can affect if the pin is low or high at idle.

The resistor value is really big compated to the voltage.

The signal. It can be either high or low. The exact value depends on your exact use case, it could be 5v, 3.3v, whatever. But because we’re working in digital logic, we only really care about 2 states, on or off, high or low