Short and sweet: pull up/pull down resistors explained
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- Опубликовано: 1 окт 2024
- Short and sweet: pull up/pull down resistors explained
A quick lesson on pull-up and pull-down resistors. How and where they are used.
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FAQ:
Me: Paul, 49 from USA
Education: United States Navy, University of California at San Diego B.S. E.E., University of Pittsburgh M.S. E.E.
Experience: United States Navy STS, Bayer Intnl Process Engineer, C.C.A.C AP of EE
Current: Retired
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New to electronics and went almost mad looking for a pullup resistor (now I know duh) but I wouldn't have figured it out without this video, thank you very much. You just gained a new subscriber
Now THAT is how you make a RUclips video! Simple, clear explanation with a nice demonstration, good sound quality, good video, not too long, not too short.
I finally got it from your video. Good sound & image quality. And no annoying music in the background! GREAT. THANKS!
Me too, I could see how a pull down worked but not sure on the pull up! This video confirmed I was over thinking it! Thanks also.
Ya. I been meaning to get the idea for a while. I actually thought it was a *type* of resistor. What I dont get is, if it didnt hurt the chip or the input to the chip to be directly connected to high or low(in either state, respectively) then why would the resistor be needed? Granted this was the simplest of examples for learning sake. I would suppose the resistance would be needed in a more advanced circuit or in an automated scenario?
Nevermind. I thought about it for a minute. To keep the circuit in a known state, not in the unknown or tristate from induced voltages.
To get rid of the rolling shutter effect on the lcd, dim the room and increase the camera's exposure. This will decrease the camera's shutter speed, which increases motion blur and causes the cycles to blend into one another (just like the eye does it).
My analogy for this is: floating is like a screen door blowing in the wind, open/close, back and forth. Pulled down is like when you latch the door's handle closed. Pullup is when you hook or tie the door open to a nail or something allowing the kids and bugs to come and go as they please.
A picture is worth 1000 words. I've read about these many a time, but, the visual with the button sealed the deal.
I love your analogy, thank you. Analogies like this really help me to understand otherwise complex subjects. Would you happen to know any RUclipsrs that teach electronics in this way?
Awsome, the Yoda of electronics explains a confusing topic "simply". Thank you for sharing your knowledge.
I almost understand. What I don't get is why you don't use two resistors with the button, one to pull up and the other to pull down. Surely the button leg without the resistor is a dead-short?
I mean, at (4:11), the button-push pulls up to the positive voltage. You say there that the button-push is doing the same thing that the resistor did but it's not. The button-push is creating a dead-short to the positive rail. And when reversed, the button-push is shorting straight to ground. I really don't get this. You say near the beginning (2:22), that you don't want shorts, that you need a resistance (within a certain range of course).
Great video Paul. Thanks for covering a topic that pros tend to think that s too simple to cover, I know it took me awhile to understand what was going on with pull up and pull down resistors. As usual you make it very easy to follow what is going on.
Thank you for this short concise explanation of this. it makes SO much more sense now rather than reading random documentation that just flies over my head, I get a practical example of what's going on and a concise explanation!
There is still something I don't quite understand, in the switch example, why do we use pull-up/pull-down resistor for the default state, but connect the other leg directly to ground/vcc?
Can you further explain the reason Input Pin 9 initially is in this third state arbitrary switching between High and Low? By looking at the circuit no voltage should be passed into Pin 9, therefore in theory it should just be Low?
Thank you very much for making this video! I too was incredibly confused with the idea of pull up and pull down resistors. It's simple, but can get quite confusing when you don't know much. This helped a lot!
Thanks! One question. So, the pull up/down resistor just acts as a small “load” upon the button push seeing as it is now connected directly to positive and ground?
(Edit) sorry, just wrapping my head around this😁. Or is the pull up/down resistor just “by passed” because of the path of least resistance to the micro controller pin out? Thanks.
This video is just like my woman. Short and sweet 👍
could u please give me the Arduino code for that whole thing please
Very interesting. I have multiple RFID units in a project. Each RFID works fine on its own. But when together they do not work. I was told i need to use pull up or pull down resistor to ensure the RFID are not all passing data at the same time. Can you advise and show the way. Thanks
you may also need decoupling capacitors
Hey! I just had a quick question, why do you need the resistor to tie them down to either 1 or 0? Why not directly use a wire and connect to ground or power?
The resistor helps define the state to either LO/HI. If you just use a wire, you're pretty much leaving it in that tri-state that he describes. (I know this is an old comment, leaving this here for other people to review if they have the same question)
@@jwilly5816 I still don't understand why a resistor is needed instead of a direct connection, like a wire.
@@lpeter1172 If you leave just a wire, it could also just be a short circuit (a low resistance path straight to ground), and it will not generate any sort of voltage drop
So, because there is a resistor, the current flows over it and that's the state (ground or positive rail, where ever the resistor is connected to) but when you press the button, the button connection has lower resistance than the resistor and thus the current rather picks that way to flow and thus it's detecting the either ground or positive rail, where the button is connected to. Right?
That's correct
Thank you lots, and I hope you are in good health
Paul, just so you know. For me two explanations like that and two math explanations per month and your channel is worth it. Hell, I have even bought products after your reviews. 5 to date. Your good, don't worry about the coming and going folks, just stay with what you know. It will all settle down. Have a good week!
Thanks for your simple explanation...I was wondering why we are shorting circuit by our own...but I just learnt what does it mean!....
Hope you have been feeling better, glad you still make vids, I love to watch them. :D
Rlly good video, thank you
Hi, nice and simple video. I really like it but to me it's still not really clear. Why does it jump around without these things? It's not really clear. Seems like the project is simply broken without this sort of bandaid. Like, why WOULD it be jumping around if the particular circuit is wholly disconnected? It's kind of like saying why does the light flicker on and off when it has no power... It wouldn't, so why does this mini-circuit do that?
isn't pin mode input_pullup the same thing?
There is a very small 10K resistor there so yes you are correct.
Yes I enjoyed it, but my question is WHERE is this random voltage coming from. Or WHAT is causing this random voltage. Especially on these Arduino or Pi's where the DC voltage is SOO CONTROLLED.... ..so my question is what is causing this fluctuation of voltages?
I’m new to learning, and I’m working a project with a plc, anyway let’s say I have 12v system and A being the controller and B being the controlled, B has a 12v supply and A has a low pwm signal, it’s pulling the voltage down from 12v correct?
You explain a lot better than my college professor. Thank you.
What this video REALLY needed as a small circuit diagram in one corner showing what connections you’re making-it was really difficult to understand what changes you were making and where you were plugging in the resistor. Also, be careful of terminology-when you were discussing the push button you said two of the terminals were “ganged” together-what does that mean? And the other two were opposite-what does that mean? Opposite of what? If each other (which is what I assumed) what does it mean to be opposite each other-when one is liw, the other is high? Iy would have taken 10 seconds to clarify this instead of making us guess. That may be very basic to you, but to someone who only knows generally what a switch does (on/off) but doesn’t understand about DPST/SPST/DPSDT (I know the terms but I only have a vague notion of what they mean.) It may be that you’ve already covered switches, in which case my second criticism doesn’t apply, but the first was a bigger problem to me anyway. As somebody starting out in electronics (I’ve soldered a couple of projects together, without understanding how it accomplished its purpose and what each part was doing), I’m really interested in the “why” and “how” of each part of a circuit. For instance, I would love to know why you picked 10K as the resistor value-I know has something to do with limiting current but there’s no understanding there. I hope these mild criticisms (I liked your presentation overall and it’s just what I needed to know) help you to improve your videos by accommodating your target audience. BTW, let me just say, we’re not looking for an engineering degree, I think most of us are looking to REALLY understand practical circuits so that we can eventually take a circuit or part of a circuit you’ve explained and put it together with other building blocks to make a unique circuit, while understanding what each part does and why it should be a different (or the same) value in our new circuit. Sorry to be so long winded, but people like you are valuable to noobs like me and I hope it’s worthwhile to help you help us! Thanks for your work!
I thought you were going to explain the actual state of high impedence itself. I guess not.
You don't have to explain what on and off is, it is common sense I suppose. But how this third state comes about and then explaining it. Furthermore to explain it in a clear simple way... that is another story.
that still does not make any sense to me. Why not just use a simple wires, for both ground and +, instead of a resistor?
Wires have low resistance on their own, so it would short circuit.
If the wire's resistance is, say, 2 milli-ohms and the voltage across it is 3.3V, the current flowing through it would be 3.3/0.002 = 1650A. That's 1650*3.3 = 5445W.
The wattage of a kettle is generally in the 1000W - 2000W range.
@@waldolemmer why use one resistor to pull down and one simple wire to pull up (or vice versa) then? according to your explanation, we should 2 resistors. He uses 1 (either to pull up or down)
@@pajeet7966 I honestly don't know. I didn't understand his explanation and am still doing research on this. If I can figure it out, I'll get back to you.
Basic yet powerful fundamental concept to grasp. Hope you're feeling better, at least the crazy heat broke.
Yes it was in the 60's last night.
liking that!
THANK YOU SOOOOO Much Best explanation ever The visual made it click for me. Count me in New subscriber
I learned about this the hard way, I needed a pull up resistor for my game using rotary encoder but couldn't figure out why the voltage I was getting from them was always very low but not 0. It was an annoying problem. There is such a big difference Practice and theory. Thanks explaining it to us.
Not only did I learn about pullup/down resistors but I also never knew the pins on those push button switches where arranged like that!!!! Ones farthest apart, ganged together, ones closest, opposites!!!! Never need to check with my meter for continuity again LOLOLOLOL Crazy!
One clarification: When he says "move the resistor" at 5:32, his finger temporarily covers up the action of putting the resistor's lead in the breadboard. And when his finger moves away, it looks for all the world like it's been pushed into the negative rail (as the switch jumper is about to be), but it's apparently just bent in a way that makes it look that way, and it's actually pushed into the positive rail.
That was great! I love the redundancy of going through it again with an interactive circuit. Simple as it may be I was struggling with this concept. Lol thanks! 👍
Thanks
You definitely got my subscription. Awesome explanation ♥️
We'll explained Paul. You wouldn't have to worry about the heat if you were here in Scotland! We've had to fire up the woodburner as autumn seems to have arrived here!
Thank you. You explained it in a way that someone who doesn't understand much about electronics (like me) can understand it. Question - if the pin is in HiZ state, can it's state not be changed via the code instead of using a resistor? Can I not set a pin to high or low and avoid using resistors?
Kinda new to electronics and I actually made a software solution to this because I didn't know that I could jsut enable the pulldown resistor in the pi pico with a few extra letters and not have to measure 50 different times and only activate if all 50 are high(and even then it didn't work properly).....
This doesn't help me understand this at all. Why is "2k to 4k okay to start with"? Who decided those values? How does ohm's law come into play here? It's all completely arbitrary...
Why do they float ?
thank you for explanation. but I still don't get it. although that information about the 3rd state of a button was useful.
Great video, but now I have another question. Why does pin 9 go low when you connect it to ground with the button? Why does the voltage at pin 9 drop so much?
Newbie. Just started learning about electronics. This is my first pass with regard to pull up resistors. I still don’t entirely understand how they work or to use them but know that by the 6th or 7th pass, it will start to sink in. ;)
Stupid question, is either of the 2 better for an arduino input?
do they consume the same amount of energy?
do they have any differences apart from the logical value?
Wow, really fantastic, I understand it well now and can understand the circuits shown in class a lot better now... Appreciate it
Can you tell me, why the pin is in a tri-state at all? On what base is the processor thinking it's 1 and one second later it's 0? Is this some kind of internal power flicker?
Mouth noises lol
I suggest you keep your mic further away from your mouth and don't eat before recording.
I guess it may be informative, but the god awful smacking noise you make every time you start talking is unbearable. I made it like 2 mins in and had to turn it off.
Your videos are the best I have seen, Thank you for your help and hard work. Hope youtube is treating you well
You just wired it up... didnt explain anything lol. Thumbs down.
I’ve been doing this didn't know it was called pull up/down makes sense though
Off is not negative. It is zero volts. Negative implies you are reading a voltage below zero.
You know that feeling when you have an aha moment? That just happens to me. 👍
so the video deserves a thumbs up but i cant get myself to give since it's currently at 4444 so once that changes i will give it one
Still didn't explain why you need the resistor.
Yes I did. Keeps circuit from floating.
@@learnelectronics nope, connecting the voltage supply directly to input without switch in between does. But, to allow for logic low voltage, a resistor has to be added or it will short circuit. @ShishakliAus
Thank you very much, short and sweet explanation indeed :)
Finally now I understand the concept. It's amazing how your video made it so easy to understand. Thanks buddy.
Me too! Hope you're feeling better. Ahh, my daily fix of electronics, 😀.
I don't understand how the pull down resistor configuration does not cause a short...
Thank you, sir, I appreciate it sincerely.
This explains so much. Thank you for the video!!
That's a nice explanation, thank you. But what is weird is why should a pin be in an uncertain condition. Either voltage is applied, or it isn't. 1 or 0. Where is the intermediate value or "floating" coming from to begin with? Thank you.
It comes from inducted and parasitic voltages present in the IC.
It gets rid of the noise that could be confused for a 1 or a 0 by bleeding off to ground or pos. Without creating a short, by having some resistance.
When pulling down, it acts as a load, preventing a short circuit. When pulling up, it acts as a current limiter, right?
@@Max_Moura It's not there as short circuit prevention, if you tried to bleed down without a load it would be a short circuit. Pretty sure you got that, I just wanted to clarify. So far as current limiting, I'd defer to someone else.
Simple and nice explanation. Regards! You are the man.
Good thing there isn't a pull out resistor because I never pull out.
what was displaying on his LCD screen though? I wish he showed his code for 1 min. Otherwise, it's a FANTASTIC Video! Subscribed!
nvm, he described it 1:47 "All the sketch does is a digital read of pin#9". Informative video!
I’m not good with electronics at all. I need to add a pull up resistor circuit to an aftermarket tachometer in my truck. This video finally gave me my aha moment. Thank you, I finally understand. 👍🏼👍🏼👍🏼
You can do it!
I don't see this tristate issue (flipping between on and off) when connecting a button without any resistor to raspberry pi 4 GPIO (3). What is the raspberry doing that prevents this issue?
Don't the RP2040 chips have internal pull up resistors on all gpio pins?
very nice sir, thats a lot for clear explanation, complete practical.
Exactly what I needed to know, without flooding me with info I didn't need. Awesome. Thanks for saving me an hour or so of wondering and playing around before coming to this solution!
Good job. Pull-up pull-down understood. Thanks.
I understand the concept partially, but I still don't really understand the flow of electricity. Why do we need a pulldown resistor when the circuit isn't even complete? Surely that in itself would be LOW. Before the resistor is placed, the +5v feeds the positive rail of the breadboard, there's nothing connected on this rail, so there would be no signal sent to the white wire anyway. I think it's the tri-state that I don't understand.
Unconnected microcontroller pins will float high and low unpredictably. That's why we pull them one way or the other. It is the only way to know for sure.
Thank you, Sir. You have a very comprehensive video.
Is a pull up resistor just a resistor placed in a certain place in circuit or is it a separate type of device to a regular resistor?
Can I put them in series, aka take 5x10k Ohm resistors to reach the needed value of 50k Ohm?
Does it matter which way I place the resistor in circuit? Like is there a polarity thing with them like there is with a capacitor?
Thanks.
a pull up or pull down resistor just notes it job as you said. Yes you can put them in series, parallel or a combination.
hi, instead of using resistors can I simply connect it to the ground?
Great explanation. The penny has finally dropped. Thanks
You saved me again! Your demos are so good!!!
Thanks. Very clear explanation!
Thanks mate for this explanation! Great job!
Nice explanation. Button example locked it down.
What LCD display that you are using?
Great explanation. Thank you 🙏
I am using a mega to control a pinball machine but even with input_pullup it sometimes gets noise or something in the inputs and this causes the mega to reboot itself. If I pin mode with output and only pin mode to input pullup would this help the mega simply ignore the noise and not reset itself?
A larger resistor could help. The built in pullup is 10k.
Or do you think maybe the pull down approach would be better? with all the pins connected thru one resistor. I have a lot of switches to check in this thing.
Wonderful explanation. Thank you.
Thank you so much, it helped me alot
Thanks man, you're the best. much much appreciated.
Any time
Perfect explanation. Thanks!
great video ! would love a debouncing tutorial too
so....then why still resistor, I'm certain that if you replace the resistor with cable it'll still be the same result
im just finished another video, when the switch is pressed, there might be a power surge from true to false, hence the resistor should exist so nothing is shortcut
Thank you so much! Great Video!
Thanks! Im currently reading an entry book about Arduino and electronic and i noticed their use of 10k resistors for the buttons with absolutely no explanation. This has cleared up everything :)
well done - thank you. having that dynamic display makes a HUGE difference to the quality of this explanation. Seeing is believing!!!! The best expose of PU PD resistors I have found.
Thanks a lot....at last I understood indeed....!
That's a nice fucking pen..
Thank you for the clear demonstration! I got the official Arduino Starter kit and they started using pull-down resistors with no explanation. It was bugging me why those resistors were there but now I know!
why is that pin moving between 0 and 1 state?
thanks for your video and your time!!