Pull-up and pull-down resistors

[@sudhirpatil3434]

I watched video over n over again to make myself clear abt pull up n down res. Previously i watched couple of other videos from which i was unable to grasp. But your way of explaining things made me understand the stuff! Thx

[@trevorjames83]

That's been bugging me for a while, having only started with Arduino fairly recently. Thanks for the wonderfully simple explanation.

[@learnelectronics]

Trevor James You are welcome. I'm always here if you have questions.

[@Humanclock]

Thanks! You do a good job keeping the examples as simple as possible and not going off on long tangents. (I saw another tutorial online that had multiple switches and resistors in the circuit, that was really confusing from a newbie perspective).

[@meestawoo2840]

Best explanation so far, from all the videos I saw on this subject.

[@carlossebe2481]

Hi. This is the best explanation and demonstration I saw. The explanation is similar to all that I saw or read ... but the demonstration is fundamental, it is recorded in the mind. Thank you.

[@aydencalvin3031]

not sure if you guys gives a damn but if you are bored like me atm then you can stream pretty much all the latest series on instaflixxer. Have been streaming with my gf during the lockdown xD

[@TheMilohemlock]

You have my gratitude for explaining this in a way I can understand. If someone had made this as clear when I was in tech school, it would have changed everything for me. Thank you for being kool. Me

[@learnelectronics]

Glad to be of service

[@945-b2m]

Very well explained. Thank you!

[@isfk]

Best explanation I've seen, this clears things up, thanks.

[@learnelectronics]

isfk Thanks. My real job is teaching basic EE at the local community college.

[@alchemy1]

Most of what I have noticed is that pull up resistors is used far more than pull down. Most likely because it is the electrons that move from the ground towards so called high voltage and charges don't jump from VCC to ground. But I don't know.

[@igrewold]

Great man, thanks a lot. How do we know when to use a pull-up resistor and when to use a pull-down resistor? The decision is based on what? And what about the value(s) of the resistor(s)? Because I think in some applications(battery operated circuits/devices) losing more than needed power is a waste of energy.

[@learnelectronics]

igrewold You decide whether to use pull-up vs. pull-down based on if you want an inverted signal or not. (Pull-up = inverted). As for resistor vaule: between 5 and 10k.

[@igrewold]

Thank you

[@brettpenza5149]

I am still trying to get my head around arduino and pull-up, pull-down. This was a great video incorporating the simple circuit drawing and then the hands-on example. Great work! One question. Is that a resistor attached to the LED? And does the LED have to go back to ground to complete the circuit on the high side? Thanks again. Great stuff. Great pacing.

[@learnelectronics]

Yes it's a 220R resistor attached to the cathode. The anode is attached to the same pin as the switch (parallel). And yes, it must connect to ground to light the LED, but it has no effect on the switch.

[@WahidKhan-rx9jo]

Thnx , gr8 explanation !

[@huntingexperiences93]

Hi :) in a case of pull down. What will happened when i choose value of resistor lower then value of arduino pin? will it works or not. I think that not but for sure i will ask you :)

[@michaelpadovani9566]

Great instructional video once again sir!

[@learnelectronics]

Michael Padovani Thank you

[@avrphreak9121]

Thanks!

[@marcuscesar1343]

Great explanation.

[@codev3rtcreations]

How do you know what resistor to use? You are using 10k ohm resistor for this project. I’ve seen other videos but no one seem to explain how to calculate resistor used in pull down resistor application. Please let me know, thank you ;)

[@jonelectronics510]

You need to know the impedance of the input pin and then the logic value you want to have. For example, if a uC has a logic high threshold of 3V and you want to pull it up high, the voltage at the pin must be 3V or higher to register as a logic high. So: Input impedance: 100k Pull up resistor: 100k You can see that you would get half the Vcc at the pin, if vcc was 5v we would be under the 3V logic high threshold so would fail to be pulled high, so a lower resistor value would be needed. Another unseen danger is the capcitiance of the input pin, meaning that if you use a large resistor the switching time will start to become a problem. In reality there is quite a range of values, normally between 10k-100k will normally work.

[@jonelectronics510]

Also be aware of current, you don't want to choose a value which just sucks current.

[@danysize]

THANX !!

[@dominikbaricak9589]

Why when switch is closed in pull up mode the input is 0? It doesnt make sense from what i know about electricity. Switch and MCU is connected in paralel with VCC and when something is connected in paralel everywhere should be the SAME voltage. I dont understand that...

[@POLMAZURKA]

pull ups resister are above the switches on a schematic?.....the reverse for downs?...............

[@keithoconnor1090]

reminds me of Schrodinger's cat

[@birkhansonkan4236]

Nope i still didnt get it unfortunately! I thought the resistor was pulling it down to "Zero" (0/to the ground) so shouldnt it change the value 1 and 0 (9:01) continously when you remove the resistor?

[@igrewold]

Think about this way: we got 3 states(hi,lo & floating), the reason we need a pull-up/down is to avoid floating state because that state is making the mcu/Arduino crazy it is as if you are asking a person a yes/no question like "do you want to have dinner?" And you are getting the answer "the sky is blue!" So, you dunno whether that is a yes or a no! Maybe a simpler circuit would help in understanding it better kzbin.info/www/bejne/aXrGoGSFZ8mAm9E

[@birkhansonkan4236]

First of all thanks for your answer and i have to say i do get that part of the subject. The part i dont get is the blue wire to pin 9. Why removing that wire instead of removing the resistor at 9:01? I thought the resistor was pulling it up or down!

[@igrewold]

He removed the wire to show you how Arduino is confused from the floating state which made it fluctuate between 0 and 1 then when put the wire back into the circuit the state was 0 because of the pull down resistor. And once the button is pushed the state became 1.

[@LanceDenly]

I thought the input impedence of a MCU was very high, like at least 1Mohm. The only only current flowing into the input pin of the MCU is unwanted or "leak" current. They are more of a voltage controlled device like a MOSFET. Almost all of the current is going to flow threw the pulldown or up resistor. Again, I'm not 100% sure so I would like you to comment on this.

[@learnelectronics]

Lance Denly No the input impedence is low. This allows the Arduino to sink current as well as source it.

[@LanceDenly]

I think I'll breadboard this up because now I'm more curious about this than I was before lol. I work with PLC's so I know they are lower cause they are essentially a LED inside an isolator, I just wasn't aware that these micro's were capable of doing the same thing. Keep up the good work on the channel. Stuff like this is how we learn either from not knowing, or from being taught wrong like me lol.

[@LanceDenly]

I get 0.500mA flowing threw the 10K resistor while feeding the input high. Total circuit current was 0.500mA. I tried both sinking and sourcing on the input with the same results. I used a second DMM on the input and cranked it down to uA, but still read zero. I'm not saying that your wrong at all on how to use a pullup or pulldown. Your spot on on everything including your schematic and everything. It's just that one part where you draw an arrow and point out where most of the current flow is traveling at 7:15

[@learnelectronics]

Lance Denly check out this link for more info on Arduino current sinking: playground.arduino.cc/Main/ArduinoPinCurrentLimitations

[@LanceDenly]

those are output limits, not input

[@deadchords4919]

cool

[@learnelectronics]

Shredder thanks