EEVblog

Fundamentals Friday
What is a Schmitt trigger and how does it work?
What is hysteresis?
And how do they fix two common problems in electronics, namely slow slew rate signals on CMOS digital chip inputs causing oscillation, and noise on comparator inputs.
The issues are demonstrated first on the breadboard, then the whiteboard explanation, and then the hysteresis fix is added and demonstrated.
And how are Schmitt Triggers physically implemented in CMOS logic?
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[@MrSaydo17]

So I had this person from the IEEE laugh at my negative feedback shirt. Saying, "I only give positive feed back but am prone to oscillation."

[@EEVblog]

Nice!

[@ccc5226]

Do a program with a super high-speed counters cheap and available ns and ps :)

[@mand6029]

thanks Dave , for making electronic concepts easier and more interesting than any professor on the planet Earth, catch you next time , bye bye

[@DJSkunkieButt]

..."A fraction of a bee's dick." Your Aussie analogies never cease to make me audibly say "dafuq?"

[@heman248]

Your videos make me learn. My college only tests me. I should be paying you instead. Thank you for your videos I have learned a lot.

[@hannescamitz8575]

I've asked myself, why isn't Dave a teacher instead? Well of coarse it's because of insterests and so.

[@yssing]

Well he is sort of a teacher, he teaches using youtube :)

[@tomaszwota1465]

I think you underestimate the difficulty and hardships of running a school.

[@PankajKumar-zr3tv]

But did you pay him?

[@TheMechatronicEngineer]

@@PankajKumar-zr3tv no

[@andyaitch5322]

Excellent video Dave. You went through it the old-school way, showing the proper analogue hysteresis solution rather than what 99% of people would do, just add a Schmitt Trigger module/circuit. I also learned something from your explanation of the digital version Of course, even those who understand how it works will still pick the IC that has the Schmitt Trigger built in because, let's face it, it's easier. Kudos to you mate, you obviously have a deep understanding of electronics but also have the knack of making it entertaining and easy to follow.

[@andreasdill4329]

LOL, OpAmp isn´t anywhere near old school. The original design used tubes.

[@Bradman175]

Without watching this video, I would have just stupidly added a Schmitt trigger IC.

[@meepk633]

I know zero about electronics, but I understood this after watching. You're a good teacher.

[@Braeden123698745]

Dang, my DaveCAD license expired, my pen ran out of ink.

[@daveb5041]

"Trap for young players, lets go to the data sheet!" This seems a common theme, plus I like the way he says it.

[@marshaul]

Datasheets are the lifeblood of an electronics engineer.

[@recomoto]

Watching your lectures is a PLEASURE my man! Beauty!

[@jaideep1337]

I wish Dave could replace the profs at my university. So much fun to watch your videos Dave. Thank You

[@guatagel2454]

Thank you! If only I could travel in time 24 years ago and show this video to my past self... I've spent endless hours trying to debug my circuits. But I can show this video to my students. Thank you very much! (excuse my english)

[@miguelangelsimonfernandez5498]

In my second year at university, ages ago, I had a similar problem with a very slow counter. It worked at home but, as soon as I was showing it to the teacher it started to play these tricks on me. The thing is, the teacher didn't know why either and gave top marks anyway. Wish I had know about Mr Schmitt.

[@Antoniobeta]

Love Fundamentals Friday! It would be cool if you make videos on that category more ofthen.

[@briandecker8403]

Dave I am second year Electronic Systems Engineering student and your videos have been - to put it mildly - invaluable! Thanks for the time and effort you put into sharing your knowledge and experience - B. Decker, Cincinnati Ohio

[@paulwang5650]

Thank you so much Dave, I love coming here for these delightful crash courses on engineering.

[@FappyGnome]

Great video Dave, always good to see some educational EEVblog content in my subbox.

[@mbaker335]

We need more videos like these. You are quite skilled at these educational videos. I much prefer it to a tear down of a 40 year old bit of kit.

[@kaizen9451]

Bloody brilliant Dave. It is so much easier learning a component etc when you can put it into context.

[@Shaybay922]

Every time I watch one of Dave's videos, I want to resubscribe all over again!! They're that good! Thanks Dave - forever a fan! :)

[@dimasarifiyan3758]

Dude, after going to all other channels, that explains Schmitt Trigger, this is the best and the clearest one! thanks, man!

[@lasersbee]

Was waiting for another Tutorial. Love this stuff... Thanks Dave ;)

[@ham4ham71]

This causes so many problems in software when the hardware designer misses it. EXCELLENT VIDEO! Also the software designer should account for this and best when both do. But this is very frequently missed!

[@DominiHarling]

I thought I already knew about Schmitt triggers, but I watched and I learned something new again. Thanks Dave!

[@malergreven]

Thanks for the block, I love when you do these teaching block, it teach me a lot.

[@Antiath]

Precisly when I need to take care of input noise on a comparator, Dave gives me a solution. Great timing, thank you very much !

[@A_RosnerNZ]

I have been trying to design an overload cutout digital circuit based on a comparator measureing voltage across a shunt resistor. It was oscillating. Which I discovered after making an SMT board. Much puzzlement later I came across this video. It was literally a case of adding a single +ve feedback resistor and the problem just immediately went away. You saved me so much hassle!

[@hsxenon]

Please make more fundemantals Friday! They already helped me studying for my classes a lot.

[@VolksTrieb]

best educational videos ever.

[@firefly618]

Lord_Vader Seriously, these are the best.

[@JohnnyYenn]

Lord_Vader Got me through circuit analysis too!

[@jonathanwatmough]

Awesome stuff. I am learning so much watching these videos. Thanks Dave!

[@matooo95]

Wish I had known this a month ago, when I was designing simple comparator circuit. Now it's being manufactured and it has that oscillation problem.

[@EEVblog]

Time for a bodge!

[@CaptainDangeax]

Thank you for this video Dave. although I learned electronics for 2 years, I completely missed the slow raise time issue. I've heard of the schmitt trigger of course, but I didn't know it was so important.

[@kamalmanzukie]

uh oh

[@ryanedison5709]

You sir have be invaluable in my understanding of electronics. I have not found another KZbinr who has been more valuable to my understanding of electronics. You've been the reason I've been able to stay upbeat while dealing with problems that plague the "Young Players" as you say. Thank you from the bottom of my heart!

[@robertbeech888]

Doing Research for my 3rd yeah project (50hz phase detector) and this was awesome. Really happy I found your channel 👌

[@PyroShim]

Thank you for this video. It is a really important issue that I never thought of enough.

[@cexploreful]

This video was sooo much impressive than i ever wonder! The last part was absolutely genius!! Thank you so much!

[@Poketronics]

This was an amazing video, thanks for the refresher!

[@pravardhanus]

Wow. Now i really understood about schmitt trigger. Hats off to Mr. Dave.

[@ted356]

Excellent work, Dave!

[@pradipkhare]

Thanks Dev and it has been very useful to understand insight about it, though I have been using Schmitt trigger more for debounce signals. Thumbs up and eager to see next session.

[@321crash]

Love the fundamentals friday! Thank ya Dave!

[@jjeeva8870]

Thank you so much Dave. Your videos are really helpful to understand the fundamentals of electronics. I wish I had a teacher like you in college. Whenever I am stuck at some point I will search the concepts in your playlist first. Your video tutorial helps me a lot.

[@martingannon132]

Excellent discription Dave, thanks a lot!

[@ryanwelsh8880]

Great video Dave very clear and easy to follow!

[@TechBench]

Excellent video - theory and lots of practical examples. The best way to learn!

[@foldi001]

I read it in books before, but it is realy much better to learn it that way.

[@Spigot37Rigor]

Fantastic video! I've been considering making something like this to help my customers (I develop new logic ICs for a very large semiconductor company) but just haven't found the time to do it. So glad that you beat me to it - yours will likely help far more people than mine would!

[@DrewFolta]

When I was quite young I had this explained to me, describing why a house thermostat has two trigger levels, so that the furnace doesn't keep turning on and off, which stresses it. Recently I was talking with a friend who owns some property with a well and storage tank, and same thing so the well pump doesn't cycle too much. So much hysteresis!

[@dentakuweb]

Exactly. We've had a drought here for a few months and I've been messing with the water pump and tank lately so I checked if the system had hysteresis and it surely does. It stops pumping at 60psi and starts at 40psi. Synthesizer circuit builders love schmitt trigger inverters like the 40106 or 74C14 because they have six inverters in one IC and can be made to oscillate with just a resistor and a capacitor.

[@r.logiacco]

Finally I got what Hysteresis is and how to use a schmitt trigger: thanks a million Dave! 👍👍👍

[@tonybell1597]

Superb Dave, Wish you had been a teacher at my technical college doing electronics..... Love the fundamental Friday's. Maybe you can work this stuff into some small projects that pull all these principles together? Keep up the fine work!

[@inayathussain9236]

where i have been from so many years... your videos are very informative. thanks for your great efforts

[@Aschefr]

Thanks for the quality of your explanation ! I love those video, i'm a electronic newbie, and it is very helpful !

[@abhijithanilkumar4959]

Just beautiful Thanks Dave

[@jasonbrindamour903]

A Siglent generator I see you using.... With your slight encouragement I bought some Siglent equipt....I am learning so much at my tender age of 41...LOL. Thanks!

[@Dragonblaster1]

When I saw your op amp at the top left, I wondered, "if you're using an op amp to create a Schmitt trigger, where are the hysteresis resistors?" But of course, you took it slow and simple, as a good teacher should. An excellent tutorial.

[@MartinPHE]

Learn so much from these Videos Dave, Thank you so much

[@l1t7l3ph0o7]

I love your explanation of the schmitt trigger, I use them a lot in my arduino projects. If only this video existed when I was learning about them.

[@alibargh]

Thank you very much. Your teaching videos are perfect. Please make more of these.

[@arongooch]

Excellent video Dave. Very well explained.

[@doobedoobedo1]

Excellent as always

[@mrfrog8502]

Very well explained. Thanks Dave.

[@petaks01]

Excellent explanation as always!

[@symik3]

Keep up the good work, awesome video!

[@snaprollinpitts]

thanks Dave, another great tutorial!!!

[@tom7]

Good explanation :)

[@srijal]

Our 74161s at lab would sometimes go crazy with the old clanky clock generator we had, and we would blame the ICs. I think I know the actual reason now! Thanks Dave!

[@stargazer7644]

I love these. Thanks Dave!

[@bobblaine1437]

Thanks, Dave. Great stuff!

[@ao41tr]

Thanks Otto Schmitt, thanks Dave. It is very nice and helpful tutorial.

[@apexmike849]

Super video, very clear explanation - blowing the rust out ;-)

[@clacktronics]

Keep it up! Love the educational videos

[@Len02013]

Thanks a heap, that solved my problem. I wish I knew about this earlier. I was originally thinking it was noise in the data line, but after this video and a simple resistor did the trick :)

[@LittleRainGames]

Some of these sound bites are gold!

[@stevetobias4890]

Cool explanation, thank you

[@victorsalvi_]

Thanks Dave, very informative

[@stichter51]

Thanks, Dave. I was familiar with physical hysteresis, as in old electro-mechanical thermostats. Didn't know the concept was used in electronics too.

[@seaarg]

Dave, if you are not already, you should be a teacher. Great tutorials and the aussie accent is a plus... love it. Greetings from Argentina.

[@Brainstorm4300]

I came across schmitt trigger when I was thinking of a hardware solution for button de-bouncing. I didn't know about STs so I made a 555 circuit to provide the hysteresis. Later I found out about ST and life was easier.

[@MD-vs9ff]

Brainstorm4300 Check your micro's data sheet. AVRs have an internal Schmitt trigger on their input circuit, the micro you're using might also. an external Schmitt circuit may be unnecessary.

[@Brainstorm4300]

Mark Dowd I know. It was for a circuit completely made of 74 and 4000 series ics otherwise I'd have just used my software debounce routine.

[@xmenxwk]

You can avoid de-bouncing just by software.

[@kemikao]

Great video!

[@MeiklesAndDimes]

I liked how you started the video with the breadboard and demo.

[@NorbertHarrer]

Ahh wonderful stuff. Very well explained. Well done. Thank you!!!

[@Inesophet]

nice, i learned something thanks dave!

[@GeorgeGraves]

Great video - good lesson. thumbs up!

[@flashcorp76]

Aw, bloody beautifull, knew all about schmitt triggers, but I love the explanation😀

[@rolandosalgado1552]

Thanks for share , Dave, 👌

[@peterdkay]

At 25:45 you see two oscillations. One at 0.5V peak and the other at 1.5V peak. The 1.5V peak could still cause problems. A small capacitor (10pF) across the positive feedback resistor can fix that problem.

[@user-cy7st6bw4b]

Finally, I understand. Thanks a lot!

[@Matthias051]

Thank you so much again for your awesome video. I loved it very much

[@robertvaldimarsson2109]

Very helpfull video and very well explained. Thank you.

[@tohopes]

So, positive feedback yields hysteresis / makes the output sticky.

[@ashkananisi5181]

You are absolutely good! more video about Electronic please!

[@teknikal_domain]

"It only needs to be a s--- fraction, half a bee's dick, a smidgen above or below..." -Dave, 2016 you made my day with that remark.

[@byronwatkins2565]

Positive feedback for digital hysteresis can come from two series inverters; A=not(not A). The feedback element (say 1 MOhm) connects the output to the first gates and the input passes through a series resistor (say 10 kOhm) before the first gates. These choices give about Vcc/100 hysteresis.

[@evantorrey2779]

Thanks for doing my professor's job.

[@jessstuart7495]

I make a slight distinction between a "Schmitt Trigger" and a "Comparitor with Hysteresis". A schmitt trigger will "latch" into one state once triggered, and will stay there until the input transistions to close to the opposite state (large amount of hysteresis). "Comparitors with Hysteresis" generally just have enough hysteresis to avoid multiple transitions due to input noise, and will transition close to the designed threshold (small amount of hysteresis). Don't use Schmitt Trigger IC's where the transition voltage level is important.

[@bttrs]

Crazy! Just today I got my art of electronics an the first page I open is about schmitt triggers, also on friday I had a lab exam in my university about schmitt trigger nand gates! What a coincidence.

[@kttkttkt]

Ahh, fundamental fridays, i wish you did more of this.

[@bigfoottoo2841]

good one Dave

[@Diamonddrake]

Great video dave! Always a fan of fundamentals Friday

[@vinitshandilya]

This one is so easy to understand as compared to the transistor version.

[@spypruduktion]

Super simple, that Schmitt guy was one smart cookie

[@Tom5TomEntertainment]

I am very confused but also intrigued.

[@EEVblog]

A perfectly fine state to be in!

[@taitano12]

In fact, being confused and intrigued is the best state to be in when learning - provided you use it as incentive to learn more.