EEVblog

Dave answers a viewer technical question about why his circuit is acting up, and goes through a design review outlining the possible problems.
Level translation, clocking, schmitt triggers, line driving, loading, buffering, bypassing, and other aspects are discussed.
If you want to see more design reviews like this please drop a like and comment.
Schitt Trigger Tutorial: • EEVblog #941 - Schmitt...
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[@chrisgreece52]

A series like this is an AMAZING idea! It will give everyone the chance to learn about circuit and PCB design.

[@DennisXiloj]

You may require the problem to be posted on the forum before you review them so you don't get inundated with requests that will never be published

[@chitlitlah]

Even if it receives an answer on the forum first, it would still be cool for others to be able to watch a video with the most important suggestions put into a visual format to more easily learn from it.

[@EEVblog]

@@DennisXiloj If I put out the call then I'd expect to only do like 1% of them. I'd have to explain up front those are the odds.

[@BaconbuttywithCheese]

@@EEVblog It is very cool to hear your explainations audibly, rather than raking through a few forum posts. Time and effort well spent DJ.

[@EEVblog]

@@BaconbuttywithCheese These videos are actually quite easy to do, as I don't prepare anything, I just hit record and then waffle on as things come to mind and hopefully useful stuff comes out and I don't miss much. There is the big risk though of missing something really obvious.

[@andymouse]

I probably speak for a lot of your viewers, we would love a series of this format where you walk through a real world viewer design and offer help and opinions and maybe solutions to problems and also general guide lines on PCB design...I personal would love it ! if anybody reads this and agrees please add your comment...cheers.

[@chitlitlah]

I concur. Having an expert look at beginner to intermediate designs and point out how they could be improved can catch a lot of stuff Dave takes for granted and doesn't think to mention while doing a tutorial. I'm trying to get into simple design like this and videos of this nature would be very helpful.

[@frankowalker4662]

Yes, I would be educational.

[@kareljina4105]

Absolutely

[@ChurchOfTheHolyMho]

I often wish I could build something, but haven't tried. Watching peer reviews of other novice / intermediate designs would certainly be informative and build confidence.

[@azyfloof]

Second this. I'd love to see user submitted projects/PCBs that can be analysed and reviewed. Even for working PCBs as "What do you think of this?" type situation

[@monotrope]

Definitely continue this series, this is like code review for hardware engineers, super helpful.

[@CloudandZack1st]

Lol I subscribed years ago thinking your channel was more geared towards content like this. I was never disappointed and now I am even happier haha.

[@max_kl]

I wish he did more of it

[@EEVblog]

My channel has always been an electic mix of content.

[@TheHuesSciTech]

@@EEVblog I like the world "electic" -- it's like halfway between "eclectic" and "electric", which is a pretty good description of your channel :-)

[@kevinwingfield2007]

@@TheHuesSciTech I saw what you did there :-)

[@almostanengineer]

I have learnt more in this one short video than I have in a dozen others, please do more like this :)

[@mdchethan]

please continue this series Dave, it's interesting.

[@jaycee1980]

TI's TPIC6C595 is worth looking at. It's a 595 type shift register, but with open drain outputs designed to directly drive relays, lamps etc

[@Ghlargh]

Even just 74AC595, that one can drive 24mA.

[@mfryer100]

This is wonderful. This not only helps the original designer but other people like me that might overlook so many issues. I really look forward to more videos like this.

[@skye5132]

Wow thanks very much! I'm working on my first PCB project with 74HC595 chips right now and this is a big help.

[@mikemike7001]

There's nothing more enjoyable than following Dave down (or even half way down) a few rabbit holes. A welcome distraction from current (not the electrical kind) events. There are so many considerations when designing even a simple board like this that I sometimes wonder why anything I design actually works. If I don't learn something new from a video like this, I'm at least reminded of a few things I shouldn't forget even when using some classic parts.

[@EEVblog]

You usually need something to go wrong in order to learn all the way that things can go wrong!

[@mikemike7001]

@@EEVblog Of course, it's always better when things go wrong in the lab rather than in the field. And it's nice to learn from other engineers' experience as well as your own. You do an excellent job at sharing yours. I never mind if you waffle on a bit. Hm. The idea of waffles is making me hungry. Thanks once again.

[@kei_otake]

This is the first EEVBlog video I'm watching after getting through most of Ben Eater's 8-bit computer project videos, and being able to understand everything so much more is amazing!!

[@juweinert]

To be honest, I really love all the content! The tear downs, the mailbag...! But your more informational content is what broad me to your channel. I love to hear and see you talking about these things as exactly this is what's missing in other forms of education. I can google formulas and may even be able to properly understand things after a while. But in the project videos, in the design reviews (should be about your second or third?), deep dives in datasheets... THIS is where we can pick up things that are not available in any other format (apart maybe from apprenticeships), little tips tricks, things to watch out for, all these 20year-experience-things. Thanks, Dave! And if you'd like to do these things more I'd be thoroughly pleased :-)

[@koffibanan3099]

I love this. With almost every tangent you learn something new, or at least refresh some of the stuff you should know already :) Looking forward to more of these. Along with fundamentals and repair, these type of videos are my favourite. Thanks Dave!

[@lachydunne1512]

I don’t really understand much of this but this guys passionate explanations make me excited to learn, I know I’ll come back to these videos and they’ll be a great resource.

[@lloydruberus]

For those that matter, these are the videos we want to watch! This type of video might not get the most views, but it's immensely valuable and interesting for those of us working on similar problems.

[@ovalteen4404]

And further advice: Use correct time units so you don't fire off the entire show in under a second ;)

[@aholder4471]

This would definitely make a great series.

[@PilotPlater]

lots of lessons learned and places to come-a-gutsa, thanks Dave!

[@Artichoke4Head]

Appreciate you effort helping so many others learn nitty gritties of your trade! thanks alot

[@miguelangellopezdibenedett9783]

love this masterclass. so much information in such a short video.

[@7d177m412]

There is the version of the shift register with TTL inputs (74HCT595) that detects n high level above 2V. Maybe worth a test as a simple replacement.

[@EEVblog]

Yes, should have mentioned that.

[@eDoc2020]

I was thinking the same. If it's desired to add the input/output buffers then you could use something like the 74HCT14 Schmitt trigger inverter with the TTL compatible inputs. Of course since this is an inverter the code would need to be changed, I'm not sure if this is an option or not. (Two inverters equals a buffer)

[@kautzz]

I’m hooked, best way to learn! Please make these reviews a regular thing.

[@benjaminbadrakh1644]

Another amazing video. Learned a lot from this video.

[@academicpachyderm5155]

"Worst diagram ever" -- Did your DaveCad license expire?

[@xotmatrix]

As a delinquent electronics nerd struggling to get back into it, I really appreciate when you take the time to do instructive videos like this.

[@huntzkush]

Awesome video! Very kind of you to assist.

[@michael-gary-scott]

Would love to see more of this. As a beginner with PCB design I could have opened a million and one tabs with all the things you've mentioned. This video is definitely going into my collection of resources.

[@Haamedtm]

Thanks Dave, please do videos like this more often.

[@leogray1091]

Love this video. Thank for taking the time to share the knowledge. Such traps for yong players are quite hard to find ourself, great for videos like this to point them out.

[@CircularMirror7]

Neat idea using real world examples of circuits with problems and giving your opinions on it. I have read quite about Schmitt triggers and their uses. Just never played too much with them for this case use. I would love to see more circuits that are having problem and can be solved by you giving your knowledge on the subject. Great learning experience.

[@yesyes_uk]

Please make more of these. This is extremely educational.

[@YoutubeBorkedMyOldHandle_why]

Now the thing about forums is that you actually have to read stuff, if you're going to learn anything. It's a lot more fun to sit back, glass in hand, and watch Dave explain it all. So ... Great Job! ... 2 thumbs up from me, for this kind of video.

[@Ty-vr9cd]

. Big up to you Dave, love your content and makes me aspire to study harder and aspire to greater heights in the beautiful field of electronics. Ty from South Africa

[@yazeed.momani]

Thumbs-up to have such content as a series!

[@bru2al1tyusa82]

I agree a series like this would be super helpful for me...

[@i_never_asked_for_an_alias]

Well addressed. Great educational video even as a reminder.

[@randycarter2001]

The Raspberry Pi is a 3.3v chip. Your devices hooked up to the I-O connector must be compatible. The Pi has a very limited 3.3v power output. The Vcc voltage isn't specified. Assuming it's 5v from the relay board this shifts the 595's Vih to over 3.15v With the Pi only putting out 3.3v as a logic high MAXIMUM. The margin is to slim for reliable operation. Try using the SN74LS595 for a lower Vih of 2v.

[@Gengh13]

Or the HCT version.

[@chiragbirla9055]

Would love to see similar content or possibly a series of videos dedicated to PCB design reviews like this.

[@panceish]

Definitely continue this series.

[@macstr1k3rMK]

make it a series

[@Evanturar]

Fantastic segment Dave!

[@kozmaz87]

LED finally someone!!! Yes it is LED. Simple. Why do people make their lives harder spelling it out? Thanks Dave. You are the man.

[@cubeistgames7985]

One can also use the OE line and hold all the lines high impedance, so the registers are only needed if you need to hold the previous values’ outputs while loading new values.

[@MikeBramm]

Nice work Professor. This would make a great series.

[@protonjinx]

"I could do a whole episode on something like this" he says on an episode about this.

[@tomgeorge3726]

Hi Dave, a great idea for basic PCB projects like this, not complicated and using basic PCB design principles and datasheet research.👍👍👍👍👍

[@johnsonlam]

Learning is always fantastic, Dave may pick some really "come and get you" design to discuss, learn from error is always much impressive than straight forward from the book.

[@bretthaupt1019]

I really enjoy this idea. It is reminiscent of your educational series, but I think the less textbook-esque design reviews is great middle ground between theory and professionally designed circuits from teardowns

[@cuteswan]

BTW Every so often your glasses were reflecting something green (I'm guessing), letting us see right through your head. Freaky! 🙂 Still, awesome lesson on all the traps for young signals. Thanks.

[@EEVblog]

Yeah, just noticed that it was my camcorder LCD (which is mostly the green background of course)

[@fpgaguy]

Oh how many times I have seen this problem, In fact I just finished simulating a clock layout a week ago before it went out. Yes please you should have an endless stream of reviews and we will all learn

[@1082511]

Great video! I'd love it if you decided to make this a series!

[@bengrant4724]

Love the idea Dave!

[@ohmannhey]

Great Format ... very good!

[@rishikeshs6398]

Design review is soo helpful thanks

[@roguethinker6284]

Superb video! Dave is Legend

[@ahutton72]

I loved this! More please.

[@dombayan]

I think it's a great idea to continue wwth this format, it's priceless!

[@BersekViking]

The Raspberry Pie is a 3.3v device used for driving 5v logic. That is asking for trouble with noise. You need to use logic level converters.

[@monotrope]

Your point on high-frequency probing is never taught in college where I come from. We have a lot of situations like these where we know the theory and working of a circuit but end up with seemingly random errors like the OP is facing.

[@mohamedtebbo123]

Oh yeah , this is good !!! Keep doing content like this !!!

[@ahocan100]

this video deserves more than one like

[@thomasbecker9676]

I've been designing circuits and PCBs as a hobbyist for years now, and I still don't understand shift registers. Also, I use JLCPCB for the boards I make and sell, and have been very pleased with what I get. I'm that guy that gets the flat black soldermask. :D And I love ULN2803 and 2804s. They save so much space when doing through-hole

[@Francesco-bu1hh]

Very good Dave. Please do series on this topic.

[@bgitego]

Hi Dave, would love to see more mix signal layout example specifically microcontroller with ADC, and DAC. perhaps some examples of good isolation... This is a great series by the way, slot can be learn from failure ...

[@frankgrudge8823]

Loved it Dave more vids like this pls pls pls!!!

[@nixonnelson5181]

Thanks! i learned something from this video .

[@markuscwatson]

Great idea for a series

[@PeterCCamilleri]

Interesting analysis!

[@ThinklikeTesla]

Art of Electronics has the most wonderful explanation of transmission lines and termination. I don't think I ever really understood it before reading that. Also, yes to more reviews. Have guest reviewers if necessary to lighten the workload.

[@jeremyu.9093]

Hey Dave grate video, like to see more like this in the future if you are willing. vary cool

[@TheAdminist]

Yes please Dave!

[@dilbyjones]

Whooooo! This is awesome

[@efa666]

I loved the way you converted .01u to 10n without missing a beat lol

[@VincentFischer]

'Dave does your homework' would be a great title for this kind of video

[@drrobotnik5376]

Love the design videos more more more

[@Chupacabras222]

Yes, more please.

[@tuttocrafting]

I would like to have a deep dive into signal integrity for 74 series logic. That would be awesome!

[@BMR86]

Video... SAVED!

[@EEVblog]

You are now on the KZbin naughty list :->

[@Brainstorm4300]

I like this kind of video and these could be very helpful to learn to do things properly by following someone who has been in the industry for a long time. However, it would be great if you reviewed some more complex boards/designs or tackled more complicated mistakes/issues. Thanks for the video!

[@Helmut314]

More like this, please!

[@eebaker699]

As a newbie electronic hobbyist. I found this a great discussion. Can you make more like this please? I can't believe you made this video unscripted. I found it packed with useful information and ideas. Thank you for sharing your thoughts.😁

[@vipin295ster]

Great content would like to see more

[@per-5786]

Definitely like this

[@janikarkkainen3904]

I do enjoy the occasional video on your channel every now and then, But I'm gonna parrot others and say that I'd love to see more videos like this. I feel like I learned more during this video than I did in the last couple of months, and my project has nothing to do with fireworks :D

[@metalmolisher666]

I would love to see the feedback on wether or not your Analysis/Tips here worked.

[@kristiaann.9199]

I'm really liking this kind of video. I'm kind of new when it comes to circuit design. I understand a lot of the basics, but when i design something it does not always work on the PCB. Just like explained in this video there are many traps in what seem to be a simple design. Most issues are caused by things that you simply do no know when you start a design. Once you build the circuit and you notice it doesn't work as expected you research the cause and learn something about a component or circuit that you were unaware of. While i know what a schmitt trigger does, i would probably have designed such a circuit without it myself. By watching this video i will defiantly consider using one in a similar case. So yes, please continue with these design review videos. I have a circuit i would love to have your opinion about. Although i works, it would be great to see how a experienced engineer solves such a problem. In my case i'm trying to do high side current measurements, but as its a automotive application i need to secure it from long high voltage spikes (load dumps) up to 200V. This was very challenging. Its already on the forum actually. www.eevblog.com/forum/projects/pcb-design-high-current-tracks-low-voltage-measurement-(please-review)/msg3222948/ (Please note some small changes were made since my last post)

[@bitcoinwallet-tj5ue]

I am really looking forward to experiencing those "walks half way thru the room and it doesn't work anymore" things. Knowing the digital tribe has my back. If not for channels like this,I wouldn't have a shot at trying my own home automation. Bolting things together or rigging a few tons of load no problem,but this is like a whole side of things i always was wanting to explore but never came around to. So like i said,looking forward to it :-)

[@thekaduu]

Good stuff.

[@PaulGeorgeedassery]

This is amazing, prolly start a new board and pick top posts from there.

[@AndyMcBlane]

Love it!

[@McTroyd]

Add me to the cacophony (I hope?) of voices asking for more of this. Identifying pitfalls makes it possible for us ignoramuses to start asking the right questions, if nothing else, and you brought up quite a few here on a relatively simple circuit.

[@peter.stimpel]

more of this stuff, please

[@datawolk]

I like the idea of ​​making a series of it. Maybe 220V AC pcb design is interesting?

[@Soren_Marodoren]

One important thing is to draw the schematic from left to right. The serial port is in the left side followed by the 595's, 2803's and the header. This makes it very much easier to read. (The presented design is a ratnest that are difficult to debug etc.)

[@mikefochtman7164]

Great information. I knew a few of these things but learned a lot more. One question, thoughts about the single-ended 'transmission line' aspect? Something like termination at the last unit in the daisy chain? Of course if they go with input/output drivers on each board, maybe not something to worry about.

[@Thorsummoner0]

it would be kinda neat to see a similar cirtuit/application, and to take that design and redesign it for various common power levels, and show how increasing the operational power level changes a design

[@rianderous8761]

very interesting. If you share the ground however, then you just can remove the opto's and 2803?

[@bleckers]

Some of those 595's have Schmitt trigger and slow rise input filtering as well (the TI part with the same model above does at least).

[@contentnation]

I had a very similar issue when I tried such a circuit. As Dave explained, those are all valid things than can can the issue, with my design I had most of them (signal noise, no schmitt-trigger, power delivery issues). But a great explaination and good solutions. I had to learn it the hard way back then (in the mid 90s). Also another thing is safety. If this is used as a firework controller or in general controlling something dangerous and someone/thing (like a firecracker) damages the signal wire(s), everything will keep the current state (on, in some cases). This can cause nasty things. Always add at least a "green light" signal that turns off everything if going low. Also feed back the output of the last module to the controller to detect signal/wire breaks. If you want to get more secure, add a wire with a pulse signal (like 1 Hz) and a watchdog circuit on the board. If the signal does not toggle for 2 seconds, turn everything off.

[@Mutski47]

A great first try. Some of my first designs ~25 years ago were fireworks controllers using a similar serial shift register driving relays design. I had a system that worked really well and seemed very reliable. That is until I had a firing module sitting next to a 4" aerial shell rack. When the first shell was launched, strangely everything in the whole rack launched straight after. What should have been 15 shells all launched throughout the show, launched basically at once. Looked amazing! At first I thought the firing module had suffered a major failure. All the smaller fireworks worked fine. Back at the workshop and I couldn't get it to fault, with the exact same setup (same cables, same everything). My theory was there is a huge pressure wave when large fireworks are launched, and the shock wave might have caused the relays to trigger. It only takes about 1mS for the squib (electric detonator) to fire. So I tried it again on the next show. Same problem. I also tried it just with some squibs (no fireworks) and kicking the firing module. Everything went off! Since then all my designs have been solid state (MOSFET) based. No issues ever since, and I have firing modules sitting right next to 12" shells. Also be wary of what happens on power up. How are you guaranteed that all the relays are OFF!! What is happening before the raspberry PI is loaded? Is there some fail safe there? Feel free to contact me if you have questions, I've designed many fireworks controllers over the years, mostly all wireless these days.