Pull Up/Down Resistors

[@TynerPesch]

this is by far the the best description of pull up / pull down resistors i’ve come across

[@NERDfirst]

Hello and thank you very much for your comment! Glad you liked the video =)

[@toyodathon08]

Best explanation I’ve ever seen

[@NERDfirst]

Hello and thank you very much for your comment! Glad you liked the video =)

[@nijoeli]

I was trying to understand pull resistors for a couple of days now, thank you very much for this explanation:D

[@NERDfirst]

You're welcome! Very happy to be of help :)

[@Sharmamona322]

BEST EXPLANATION I HAVE A SCHOOL PROJECT RELATED TO UNO THANK YOU FOR THE HELP!!!

[@NERDfirst]

You're welcome! Glad to be of help :)

[@MrKbtor2]

I must have watched a half dozen videos and gone to 2 dozen websites but watching this finally helped me understand. Thanks!

[@NERDfirst]

You're welcome! Very happy to be of help :)

[@hootsoon9616]

Very helpful like it read my mind , was about to search this up after hearing pull up and pull down for so long

[@NERDfirst]

Hello and thank you very much for your comment! Perfect timing then, very happy to be of help =)

[@ousmanediouf9264]

Underrated Best video I've seen I guess

[@NERDfirst]

Hello and thank you very much for your comment! Glad you liked the video =)

[@Lord_Rico_XII]

Excellent explanation

[@NERDfirst]

Hello and thank you very much for your comment! Glad you liked the video :)

[@RobytheFlorentine]

very good video. Thanks from Florence, Italy

[@NERDfirst]

You're welcome! Very happy to be of help =)

[@nickstamatiou9871]

Very nice video. Maybe you could explain how to calculate the resistor value next time. Thank you so much

[@NERDfirst]

Hello and thank you very much for your comment! In my (admittedly limited) understanding, the actual resistor value shouldn't matter too much. The most critical thing to pay attention to in this setup is to ensure that there is no short circuit / excess current draw, which you can calculate using Ohm's Law - I=V÷R and ensure that I is reasonable for your setup. The secondary impact of the resistance value is the response speed as described in the second half of the video. I'm not aware if there are any formulas that can be used to calculate the response time based on the resistance, but unless you have very specific requirements, a bit of trial and error will do.

[@Srishen1]

Great stuff! Would love to see a series on transistor configurations from you! Love this , godspeed!

[@NERDfirst]

Hello and thank you very much for your comment! I happen to have a series in which I discuss how different transistor configurations can be used to build logic gates and some simple circuits. Check it out here if you like! kzbin.info/aero/PLJse9iV6ReqhHqCqtdoY3xnnx3DbxrxL_

[@vadimc2144]

Good explanation, man. Thanks. I subscribe.

[@NERDfirst]

Hello and thank you very much for your comment! Glad you liked the video =)

[@lee_johnson]

Nice keep doing whatchu doin

[@NERDfirst]

Hello and thank you for your comment! Glad you liked the video :)

[@Jechew]

This is absolutely the best video on KZbin regarding this topic that I have come across. I do want to ask how I would consider pull down in terms of current, though? Is low to 0 current a logic LOW and vice versa? In that case, would the pull down's job be to induce very low constant current to negate the effects of noise? If it is, then which way is the current going and? Lastly, I wanted to know what the other end of the microcontroller being connected to output=ground is doing in that case? Thanks.

[@NERDfirst]

Hello and thank you very much for your comment! Glad you liked my work =) To answer your questions - Actually no, a microcontroller uses voltage rather than current to take a HIGH or LOW reading. Typically, a logic LOW is close to 0V while HIGH depends on the signal voltage level of the microcontroller - This is typically either 3.3V or 5V. In terms of current, a pull-down resistor is typically of a pretty high resistance, so the current flowing through it is miniscule. This is perfectly fine since ultimately, it is the voltage that matters. As for direction of current flow, it is as you would expect with any circuit, from the point of higher voltage to that of lower voltage - At least, if you're going with the what is defined by "conventional current". I'm not so sure what you mean by your last question, though. Maybe you can elaborate a little further on that.

[@Jechew]

@@NERDfirst Thanks for the response! I seem to be a bit stuck on the meaning of Voltage. From what I know, voltage is short for voltage difference, which drives current. I understood that voltage drops over components with resistance in a running circuit. If the circuit is open, and the microcontroller is pulled down by resistor, am I wrong to assume that voltage relative to ground (we take as 0V) is 0V since there is no current? Why exactly would a pulldown stabilize and guarantee the LOW/reduce noise? Does it change the voltage on the pin despite no current?

[@Jechew]

@@NERDfirst Wait, I got an idea to my most recent reply. Could it be that since the pull down resistor and microcontroller are in series, the voltage drop across the microcontroller pin is a lot smaller than it would’ve been alone? But still, I can only imagine that be the case if there be current of some sort.

[@NERDfirst]

Hello again! In the context of digital signals, LOW is rarely exactly 0V with zero current flow. For example, for the Arduino, anything below 1.5V is interpreted as a LOW. In a practical context, there will always be a miniscule bit of current, enough for the microcontroller to read the pin.

[@samithetechsavvy6485]

thank you very much

[@NERDfirst]

You're welcome! Glad to be of help :)

[@0MrENigma0]

VERY NICE!

[@NERDfirst]

Hello and thank you very much for your comment! Glad you liked the video =)

[@swainscheps]

If the wire acts like an antenna…why do random signals flowing between ground and the pin behave differently from the random signals from before (when there was no pull down resistor)? Your animation shows there’s noise on the wire either way. So how does that solve the problem? And why does the closed switch ‘overwhelm’ the path to ground? I believe you. I’m sure you’re right. I just would love if one of the 40 KZbin videos on this topic would take a little more time and explain the why.

[@NERDfirst]

Hello and thank you for your comment! These are fair points, I'll do what I can to clarify! I'm not sure that my animation shows that there's noise on the wire - It shows an electrical connection between the pin and ground. The kind of random noise we experience when the pin is floating comes from sources like electromagnetic induction. These are typically very low energy signals and therefore, the current generated is miniscule. When a voltage source is connected, the current generated is significantly higher. It "overwhelms" the noise by being the higher-energy source, exerting a greater "force" on the electrons in the conductor. When we pull down to ground, all the stray currents have a low resistance path to ground, so they "drain" that way instead of registering on the microcontroller's pin. We can use the same line of reasoning to understand why the closed switch overrides the pull-down resistor. There are two paths for the current to flow - Through the resistor to ground, or through the microcontroller pin, which has next to no resistance. Hence, most of the current flows to the pin, allowing it to register the voltage. That's what I mean by "overwhelming" the path to ground. Let me know if this makes things clearer or if you need further clarification!

[@mr.olsen.]

Thank you for the video. I`m building a arduino grbl cnc. I got alot of problems with limit switches, how "big" resistor should i use? Have tryed 10k with no luck. Thank you.

[@NERDfirst]

Hello and thank you for your comment! I'm afraid I don't know enough about your use case to properly advise. The best I can do is to refer you to the Limit Switch page of the GRBL documentation here, I see that resistor values are given: github.com/gnea/grbl/wiki/Wiring-Limit-Switches

[@mr.olsen.]

Thank you, that helped alot 👍And Thank you for the great video.

[@davegraham7550]

Hi 0612 tv from N.Z. Nice to see a new video.

[@NERDfirst]

Hi Dave, thank you very much for your comment :)

[@OdysseyAviation]

What the red and black points moving in your circuit means. Like I still don’t understand how voltage comes from ground to microcontroller

[@NERDfirst]

Hello and thank you for your comment! Don't think of this as direction of current flow (even that has two conventions and can be drawn in "both directions"). Instead, think of this as an abstraction for which is expressed "more strongly", and what the microcontroller ultimately "sees". In reality this really is a potential divider - The voltage detected on the pin is simply the ratio of the two resistances (the latter being the miniscule resistance provided by the wire).

[@oceanjournal3028]

very nice!

[@NERDfirst]

Hello and thank you for your comment! Glad you liked the video =)

[@ousmanediouf9264]

4:06 How can current go from ground to voltage ? Shouldn't it have gone from voltage to ground ?

[@NERDfirst]

Hello again! This isn't really about current direction (which in and of itself can be drawn in both ways). This is more about what's expressed "more strongly". I debated a little about making the diagram that way also, but it is the most logical way of doing it since ground is seen at the pin of the microcontroller without any resistance, so it takes precedence.

[@ousmanediouf9264]

@@NERDfirst so, that means, in this configuration, there will be no current coming out from voltage because of the resistance ?

[@NERDfirst]

A small amount of current (_and_ voltage) will be present. However, in this context you can almost imagine it to be like a potential divider - The voltage detected by the pin is extremely low, and would certainly be interpreted by the microcontroller as LOW.

[@noaht9184]

Goated

[@NERDfirst]

Thank you! Glad you liked the video :)