Mechanical Switches are Obsolete?! Switch to a Latch Circuit! EB#53
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- čas přidán 5. 06. 2024
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In this episode of electronics basics we will be having a closer look at latch circuits. As the name suggests, a latch circuit activates/deactivates a switching element through one Set/Reset voltage input pulse and keeps it in that state. Because of that latch circuit are everywhere. They are part of other circuits or come in the form of power switches or latching relays. Let's learn all about them and build one!
Websites which were shown/used in the video:
randomnerdtutorials.com/latch...
www.mosaic-industries.com/embe...
www.learningaboutelectronics.c...
www.ti.com/lit/ds/symlink/sn7...
• EEVblog #262 - World's...
en.wikibooks.org/wiki/Digital....
www.mouser.de/ProductDetail/E...
www.mouser.de/ProductDetail/T...
www.mouser.de/ProductDetail/I...
www.google.com/search?q=latch...
Thanks to Skillshare for sponsoring this video.
0:00 What/Why Latch circuit?
1:33 Intro
2:33 Logic Gate Latch
5:31 Latching Relay
6:22 Toggle On/Off Power Latch circuit
8:57 Set/Reset Latch circuit
10:01 Verdict - Věda a technologie
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1:35 i hate this new bgm while placing those LEDs.....
Older one was awesome to hear 🤠🤠
Can you make a momentary wireless AC footswitch project? Normally open.
@@hxhdfjifzirstc894 you want to turn on ac only if someone standing near ac ? You can go for PIR sensor as it have ideal for this type of work, you may have seen automatic lights in corridors, same way you can operate AC too.
Spending 10% of your video on an advert wasn't enough?
Hi Great Scott, just a little translating advice:
in your “pro and contrast” dialog, it should be “pro and con”
pro = yes (affirmative) / con = no (negative)
I am not certain what language this stems from, my guess is either Latin, or Greek.
In most situations I still feel better when I hear and feel the "clack" of a mechanical switch
Well, that is definitely a selling point for mechanical toggle switches.
@@greatscottlab you can still include haptic feedback to the latch, so... it is something that can be a big plus
When I read "clack" I expected you to talk about relays...
And no battery drain when off.
@@greatscottlab thank you for the video I've been trying to find a good circuit for the job and you found it for me thank you for all the great videos keep it up
For battery operated devices that are used infrequently, I really prefer a mechanical switch where there is ZERO drain (other than the compulsory modelled resistance in the battery). Otherwise when you need said devices, you find dead batteries at best or corroded terminals usually.
Yes. I have a very expensive flashlight and I have to unscrew the end where the batteries go because otherwise they drain when it's not being used.
Use a mechanical latch switch. They only draw power to change state.
@@FullCircleTravis or a regular mechanical switch...
mechanical switches and relays are important in many applications due to considerations surrounding failure modes. in safety and life critical applications the failure mode is critical.
Can someone explain why? I am building a soft latching circuit myself, based on PMOS, and the leakage current when off is low enough that it would take hundreds of years to drain the battery (yes I know it would die naturally well before that). the resistance of the mosfet is also very low when on. something like 50 milli-Ω...how does that drain/corrode a battery? 😕
Don't forget you can buy latching push buttons, which when pressed and released close a pair of contacts and they remain closed until the button is pressed again.
So there are times when a latching push button is a good option and you don't need to build a load of electronics.
these are called bistable buttons, and yeah, in many cases it's enough
Unless momentary, ALL switches are latching switches. WTF are you babbling about? The TYPE of button is not the topic here... it could be push, toggle, slide, etc. UGH How did you miss the context of this discussion so completely?????
For a headphone I am designing I would like to use a nice looking button, but the circuit requires a switch or a latching button. The latching button is too tall meaning I would have to increase the case of the headphone. A circuit like this could solve my issue. I only wish a circuit of some kind existed so I wouldnt have to solder as much.
I think there is a trend to over-complicate simple devices. you did point out where latch circuits are an advantage, but there hundreds of examples where manufacturers are using a 10 component board to do the same job as a simple device. This is why you cannot repair your own tech any more it always seems to have to go back to the factory to be fixed. For example Apple phones and John Deer tractors. And now the manufacturers of cars that want you to push a button rather than open a door or not have to put a key in the ignition are failing to deliver their cars because of a micro chip shortage. I do hope the current "right to repair" movement is successful and we can stop this madness of having to pay a fortune at the garage to get the cars interior light repaired.
I agree that over-complication is an issue. I bought a used drip coffee maker (barely used, just out of its 1-year warranty) that had a latch circuit to turn it on and off. The heating elements were 230V AC and the latch circuit was 12V DC. After a few months the machine wouldn't turn on anymore. Turns out the latch circuit died, everything else was fine. So I replaced the whole latch circuit with a 230V AC 10A mechanical toggle swith with a built-in LED, which cost me 1.50€. It's been 2 years and the machine is working without an issue. These companies are sacrificing reliability and screwing over the environment for a few pennies.
this seems like an irrelevant complaint. if you're opening up a circuit to (de)solder it, that's already inaccessible to most. and whether a mechanical switch or latch is used, the complexity of repair is about the same at that point. plus you can replace it with a switch if you really want and if the application makes sense for it. "right to repair" doesn't seem to apply here
@@LC-hd5dc The point is: The smallest Replaceable Unit (SRU) used to be something like a switch or relay or some other discreet component costing about £1. Now everything is part of a complex circuit on a Printed Circuit Board (PCB) costing about £100 to replace. Sometimes you cant even replace the PCB and you have to buy the whole unit that the PCB is part of. Soon, you wont even be able to have your car/TV/fridge/washing machine repaired at all, they will all be repair-by-replacement. Then, maybe you'll look back and think, when did this all start? And you will remember, oh yes; it all began 30 years ago when they decided to replace a mechanical switch with a complex switching circuit.
I both agree with you on this, and think it's a bit out of place here. There's been countless examples of stuff being complicated for no other reason than someone either in management deciding it has to be "special" somehow and it gives no real benefit, or just engineers and designers that are lacking time to stop and think about everything from the start.
As a parallel talk I'm fully on it, being a product development engineer now it was literally the topic of our last meet up at the company (the boss saying "guys, sometimes we just need to... Stop, breathe, look at what the heck we're doing, and think: WHY is it like this? Can't it be made easier?"), and I agree right to repair just has to happen and disposable devices have to stop. People gotta stop feeding this insanity.
But I'll also say that I don't think the complaint relates to the video. There's several situations you'll want a circuit like that in place of a mechanical system. As an example, anything remote controlled. You'll not want that the only way to get that remote controlled device on and off is the mechanical button all the way at the device, neither you'll want to waste power unnecessarily with who knows, a mechanical actuator to that switch. A latch circuit solves the problem no doubt the simplest way.
This circuit being or not an unnecessary complication is always a matter of situation. It may very well be simpler than a mechanical switch even, remember a mechanical switch has to deal with contact bouncing and protecting the contacts against corrosion and arching.
Yes! I like older cars where the boot for example is held down with a simple, good old fashioned, mechanical handle. Nowadays, it's some nonsense electronic latch. Just another thing to go wrong.
Honorable mention to the humble (two coil) bistabile relay which is also set reset, and very useful in applications where a pseudo-latched run off the mill relay might draw to much power over time.
This is obviously a really interesting and problem specific solution to mechanical switches with potential benefits, but all I see when I look at a latch circuit is extra points of failure.
Depends on the use-case. Switch "bounce" can sometimes be the bigger issue.
Mechanical switches (relays, contactors, even buttons and switches meant for small loads or logic signals) have to be the number one cause of electrical failure in industry.
More than loose wire terminations and failed capacitors?
@@kuni45 But the vast majority of mechanical switches fail to a safe state. Mechanical switches also maintain fidelity for small signal AC information that would otherwise be distorted or completely destroyed by the gate logic transistors and they are immune to voltage polarity. Mechanical switches are far from obsolete.
Because you think complexity means unnecessary. Adding a square-root button to a calculator also adds an extra point of failure. Funny how calculators work for decades with all the "added points of failure." SMH
Mechanical switches are certainly not obsolete. They are simpler and cheaper for nearly all maker-type projects. Nice information to know if I ever build a project that requires it. I probably have 200 switches of a dozen or more styles and there will probably be many left when I am gone. Why change the way I do things now?
I used a latching relay to drive a fog light relay in my SUV so I could use an OEM push button. The latching relay gets power from the tail light circuit so the fog lights can only come on when the tail lights are on. When the tail lights turn off, the latching relay loses power, and the fog lights automatically turn off. They won’t turn back on again unless the OEM button is pressed.
I wanted a circuit to pop up my headlights. There was a one year only button that can keep them up with the lights off. Completely different wiring and controller... or an annoying blank off plate. I had to consider, flash to pass overide to make sure the buckets go up for that, no matter the state. Fog lights require park lights like your circuit, also should switch off with high beams since fogs and high beams are considered as 6 lights, whereas regular headlights and fog lights are considered 4, the legal limit. Automotive lights are more complicated than they look on the surface.
Thank you for saving other drivers' eyes!
Sometimes a power loss state memory can only be done with a mechanical latch.
And by "sometimes" you mean to say that PLSM is NOT unique to mechanical switches/latches. So, what was the point of your qualified statement? I have over a dozen devices in my home, including a PC, that has programmable return-from-power-loss state with NO MECHANICAL latches.
GREAT CONTENT!! I love the way you explain a circuit. I have been trying to learn electronics for some time now as a hobby. for some reason I have this mental hurdle I cant seem to get past. Yours is one of my favorite channels!
THANK YOU!
Glad to see you back to basics. Love you Great Scott.
I have been looking for something simple to use in my miniatures and only now I found you did exactly that in this video! Thanks for showing how to do this, and also explaining how the s-r latch works
Love your content. Love my mechanical switches. Compact, tactile feedback, certainty.
I teach mechatronics, the latch circuit using a relay is one of the things we teach our students, it is absolutly essential for safety in an industrial setting, love the video! keep em coming scott!
Why are electronics and electricity so complex and consumerist ?
I like how your videos are so short... yet perfectly informative.
Could still pop in a mechanical switch as the input to a set-reset latch. I understand some vintage computers did that for critical signals, so the switch bounce wouldn't fire things by mistake.
Been learning electronic as a hobby and this channel is such a gem, the pace and diagram explanations are on point. Thank for making high quality content.
Thanks for the circuit/video. I really enjoy them!
You are welcome 🙂
Using dedicated ic is kinda cheating, and I feel like transistor latch has some kind of problem where if u held down the button too short or too long a duration, undesired result can happen because of the capacitor
And the ic also uses 2 button, a t flip flop will be needed for 1 button latch, and here is where the challenge comes, it will just oscillate if the button is pushed because it is missing clock signal, a master slave configuration is needed
this video did not cover that. A latch is essentially a digital flipflop, I challenged myself to build a 1 button latch when I was new to learning flip flop, surprisingly, when I searched, everything I found was transistor latch, I had no resources to learn from and didn't know where to start, I had to figure it out myself.
And this video didn't bring anything new to the table, just the same transistor latch as every other video, in a place where latch videos are mostly transistors and digital ones are so rare to find, in most cases they just slap a flip flop on a slide and start teaching theory, where in real world a latch is more than 2 nor gates so it didnt really work in practice, it was more like a digital logic class than a latch video......
Utterly disappointed......
You're right about long & short switch presses possibly causing problems in some designs, though short presses at least usually aren't a problem.
As for the circuit itself, it doesn't mention that the "out" terminal needs to always have a current (though small) to ground in order for it to reliably work- otherwise it'll occasionally switch itself to a "default" state (which depends on the "polarity" of the transistors you're using) instead. Not usually a big deal, but something to be aware of.
This circuit _is,_ incidentally, a flip-flop, though certainly an optimized one. In particular, the capacitor gets charged to a state such that when that central switch is flipped, it will force the circuit into the _opposite_ state from what it was in before- it doesn't malfunction by oscillating when the press is too short, but instead too long, or even malfunctions by not flipping state if the switch is pressed a second time too soon after it was last pressed.
As for the normal T flipflop, the normal situation is to connect the switch to both a capacitor _and_ the clock input of the flipflop _and_ a resistor that shorts the capacitor- the capacitor will be almost instantly charged when the switch is pressed, and will stabilize the signal into the flipflop's clock input long enough for the switch to reach it's fully depressed position, where the switch _is supposed to_ tie the capacitor and clock input directly to power (or ground, for inverted-input inputs). The resistor & capacitor will control the "debounce period" that follows an interruption of the switch connection, but for the small push-switches here can reasonably be a second or less without problems. The data input, of course, needs to be tied to the flipflop's inversion output.
I felt it pretty bad when the NOR based latch was discussed - I've had nothing but trouble when making a transistorized version, it needs equal loading on it's outputs...
The NAND version is topologically the same and is very stable, even better you can make them with just 4 transistors o_O
And this reminds me of a curious circuit I remember seeing somebody posting on reddit a year ago, there are differences but it'll likely still have a problem with input voltage changes causing malfunction - definitely a no-go for anything battery operated... Though in my take on latching power-switches, I used that effect to not only detect when the battery was low - but also protected against short-circuits!
Edit: I just saw the thumbnail to ElectroNoobs' video, and that circuit looks awfully similar to this one...
Also worthy of note, GS got 4x views on his rehash of Clive's Joule Thief video - and they say something's not worth doing when it's already been done!
You are showing your gross ignorance based on a single video. Yes, this particular simplified circuit has timing issues (see my other comment for full explanation) but that doesn't mean all latching circuits built with discrete components suffer this issue. Also, IC latches are not just of the R-S type and DO NOT REQUIRE separate input triggers for toggling. You don't know enough to be criticizing.
@@DiffEQ Dude, don't just walk in and drop ad-hominems - saying "your'e stupid, stop talking" is not going to change minds; if you want to show an error, point out what went wrong and how to fix it, don't just hit at it blindly and spew insults like that...
Nothing is worse than an ignorant man accusing someone of being ignorant!
Also, don't just go 'refer to my previous comment' like that. Nobody will find it, and that's a fact...
Either repeat what you said, or put a hard link to your comment - don't just go "x marks the spot" and expect people to go find it...
Now it might seem like this guy doesn't know enough to criticize the theory / lesson here; he's absolutely qualified to judge a *video* about the basics - a video which fails to cover the basics in a complete fashion, only skims through the cool and important bits. No variations, no run-down of the caveats - I found this format in the SEPIC converter video, where that design was all hyped up - without discussing the huge drop in output efficiency, or the alternative (a flyback converter) which would achieve the same goal, and add the benefit of electrical isoation...
At least, that's what I think is being discussed here; this thread is pretty old...
Anyway, thanks for coming to my TED talk - that is all for now
A "555" latch will be much simpler to implement and also less complex and also a little cheaper. But for understanding the concept this is a great circuit. Thank you
I love the way way you present your tutorials like a really good teacher. Thanks!
Good old basics are always a pleasure. Thanks for reviewing them again.
Thanks for this great Video.
One thing you missed is the useful and for safety often used restart protection of this circuit.
For example a safe angle grinder or drilling maschine don't start by itself after replug the power cable even when the power button wasn't shut off
Great observation 👌
For future reference, if looking for wall-voltage electrically controlled relays, look at HVAC contractor stores. Every AC powered air conditioner or heat pump uses such a relay, and since they sometimes die there's a need to be able to quickly & easily replace them, thus they're sold in such stores in areas where such appliances are common. In the US, the relays are commonly refered to a "contactors".
I once found and used an interesting variation that solely used one momentary switch, one DPDT latching relay, and a couple of resistors, caps and diodes. Basically cross wiring the relay and using the cap voltage to provide the voltage spike to flip the relay over. It had issues if not switched in a long time as the caps slowly drained due to parasitics. But I thought it clever.
Your version though is cheaper and likely more relaible (and allows more current). I like it!!!
I've made a nice PCB that toggles a switch output on button single press, double-press, long press, etc., with debouncing. And it has an I2C and serial interface. It's very neat.
Good for you. And where is it?
Good video. Interesting information too. I used to use the 555 timer latch circuit for some projects years ago. I thought it was a neat little circuit.
There is much less chance of magic blue smoke with a switch.
Look at new ship controls. You loose ship controls because of some electronics failure. Now you are just along the ride as the ship rams the dock or other ship.
Or bridge.
Have to say, for like my Bench Power Supply, Oscilloscope, and Frequency Generator they all had to have physical latching buttons or rocker switches, removing the slightest possibility of a logical malfunction of a momentary latching _circuit_.
This is an argument from ignorance as you IGNORE the fact that the entire device is billions of transistors working ALL THE TIME. And you're worried about the power-on circuit failure, only??????
The ergonomics of a mechanical switch are unique. They will not be replaced where they make sense.
A few years ago I bought a nice lit switch for my bench power supply (based on an old ATX PSU). Turned out it was a momentary button, while the PSU needed a latching switch. So instead of buying another switch (it wasn't a cheap switch) I built a latching circuit like the one you are using. I additionally put in an opto-isolator between the circuit and the PSU though.
I made a similar system for an automatic water refill for a salt water aquarium. Worked very well.
Simple circuit explained in a simple way. Great work!
Glad you liked it!
I love the older this channel gets the more confidence you got with making videos and putting some hood humor in
A long time ago I criticized your channel. I was so stupid. This is one of the BEST electronics channels online now. Your simple explanations are so useful and concise. You really improved the production value as well. Anyway, thank you for such excellent content. Cheers! W0XO Jonathan
Dunning-Kruger effect. Most people, however, never learn enough to realize how little they knew when they were so very confident of their own abilities. Good on you!
I'm curious to know what the criticism was back then? I'm a new electronics student, and I believe in learning from all types of questions! It would be interesting to hear your perspective, knowing now that it has changed.
No pressure though, take care!
I like that latching relay in your consumer unit, wish they were more common here in the UK, would certainly make smart home stuff simpler than having to install separate modules to each lighting circuit in the house each with their own nuances.
Great Video! 👍
... And long live the *Stromstoßrelais* !
Haha YES!
I did 2 years in college. And 3 year working in electrical control systems industrial working on draw bridges. Now I have a greater knowledge of ladder logic and logic gate. Thanks bro.
I use a power latch circuit for my bicycle automatic shifter. The cadence reed switch latches it on (also an input) and the Arduino switches it off if 0 speed for 30 seconds. Works great and no power draw when off.
Great Circuit for high current. FYI the Momentary button 1-2 is floating when off. I made this for a project and it would randomly turn on. Use a 100k ohm or more resistor to Tie the 1-2 of the switch to GND and no more problem
Great video @GreatScott! Interesting thing to note is how much current does it use when on standby as I needed to use this latch circuit on coin cell. Since coin cells dont have alot of power, it would be helpful to have a latching circuit to turn off after use or when a specific event occurs.
I love latch circuits. Very excited to see this video.
OOH I really like that! I think I am going to have to use that in more things. So far I have only used "amplification" switches which are just a small physical switches that turn on and off a mosfet or enable pin.
I could have used this video 6 months ago when trying to implement this for a project! Had lots of issues of the latch resetting itself because I didnt use a capacitor as you mentioned. Ended up using an arduino instead.
In equipment reviews often a mechanical on/off switch is seen as a good thing. I agree. I would never use a latch circuit in anything I build as it is just a complicated and expensive solution to something that is not a problem. An electronic light switch that was widely used and prone to remote activation would be a hugely entertaining discovery. In a winters evening you could take a dog for a walk and switch peoples lights off in a block of flats and listen to the residents blundering around in the dark to turn them back on. Then in summer walk the same dog at three in the morning and turn them all back on. Even bad design can be fun in a prankster kind of way.
10:08 You are exceeding the input common mode voltage (max of VCC - 1.7V) for the LM358 opamp using this high-side current sense. This can lead to some odd circuit behavior in your difference amp.
Thanks for the feedback. So far it worked just fine.
@@greatscottlab "So far it has worked just fine"; one of the most dangerous statements I hear with regard to circuit operation. Yes, it works in this configuration, but you are reying on the stress margins the designer/manufacturer put into this LM358. Another brand of LM358 may not have the same margins, and could fail if used in the same manner. For long term, i.e. product level, reliability components must be operated within datasheet parameters, often with some additonal margin to boot. You're showing how a circuit can work, but not highlighting risks that may be exposed by this configuration. This can be the difference between "hacking" electronic circuts and designing them.
@@donbarr9487 Aha!
They have a latching circuit for the lights in the bathroom at my work. It has a motion sensor and a timer. It has a rocker switch that always returns to the middle position up for on down for off. If turned on the timer and latching circuit are activated. If after 10 minutes no motion is detected the light turns off. The sensor still works for some time after in case someone is sitting too long.
I used to make this kind of circuit with a PNP and NPN Transistor mix. Pretty useful.
5:37 ElectroBoom must be so proud 😆
This toggle circuit works great with BC337 / IRFU9024 . When first powered, it turns the mosfet ON. Also, the LED is a must. If you don't use the LED (or a diode) in parallel with the output, the output becomes unstable and prefers to latch to 0V. I was searching for an electronic end stop and this is just amazing thanks for sharing
For mains voltage applications an important failure mode of electronic switches (latch or not) is Failing On, which is often undesirable or even dangerous.
This is a failure mode that is very rare in mechanical switches.
Failing On can be caused by component failure or by high voltage pulses on the mains voltage.
These pulses can be caused by (inductive) switching actions or can be induced by lightning, even without a direct strike.
Therefore I prefer to have at least an (additional) mechanical means of switching.
At the industrial level, having mechanical switches and buttons are far more useful than electronic latches, because they ensure a clear break in the line.
I won’t mention it again, but I have a challenge for Great Scott! Build a video monitor camera system that sits under the workbench and tracks dropped items, with a laser pointer to show you where the tiny screw, resistor, or whatever you dropped actually ended up!
The savings in man/hours looking for the tiny item alone might save millions of hours! I have been known to drop the same item up to three times, and spend a half hour trying to find it. Amazing how far they can bounce and where they can end up.
Would be so cool to have it mounted under the workbench, and a laser pointer shows where it went (or as far as last point in space seen, in case it went out of sight.
I have a personal rule that if I don't find the dropped item within 10 seconds, it is lost to the abyss. Life is too short to be on my hands and knees looking for a 10 cent component. It also focuses my attention when handling expensive and/or limited supply components.
@@msmith2961 it’s a good philosophy. I find though often the tiny little item I dropped is the last one, or the only one. It’s either find it, or spend an hour finding a replacement, ordering it, and waiting for it.
@@shader26 it's guaranteed that it'll be found in the last place you look, so just start there 🙃
@@dubmob151 thanks, but I tried it and it ended up being the first place I would have looked.
@@shader26 😂
Replacing 1 simple component by multiple other components may result in: more expensive, more complicated, more points of failure, more space requirements and more assembly costs. There better be enough benefits to make this idea valuable.
Thanks for the educational video! I might find it useful for future projects.
Brilliant! Thanks a bunch, dude! 😃
Stay safe and creative there! 🖖😊
I found your video after coming up with a similar circuit, except mine uses a P channel mosfet like yours but I used a single SCR for the latching. With this circuit there is no race against time in cycling the momentary contact switch and the button can be depressed indefinitely or cycled quickly to change state. My circuit does however require 3 capacitors. Component count is about the same as yours. Thanks for the video.
I absolutely love your channel.
4:45 when i first got into electronics (after reading and watching a bunch) and ordering my first arduino and similar stuff, i wanted to build something but was missing that SR latch, china ordered took months to arrive, in the mean time my pcb had the IC header on there, with a custom circuit board of a nor gate in it ^^
Haha, really the right video for me :D I plan a project and thought about this many times while showering. Thank you for freeing my mind, Scott :)
thanks for all helping video and content,your so amazing
Thanks for this. I will need to watch it many times to fully digest it but I think it should help with an electromechanical controler I'm building.
Perfect video as always :) Thank you! Danke schön!
I have been watching your channel for a few years now, great vid as always!
Awesome! Thank you!
@@greatscottlab No problem mate, keep the good content coming!
There are many uses for a latch circuit, swapping an active circuit with quite a few components, a cheap chinese momentary switch and a relay in place of a mechanical switch that is going to work problem free for as long as 50+ years, i assure you it isn't one.
But since this video is more about explaining the latch circuit in general i really appreciated watching the video as you get into deep explanation, also 555 does wonders.
5:37 Electro Boom moment
Again a great video. Cheers Scott🙃
He really left the "qwiss question" in. Love it.
Great idea for a video! I like the "basic" in it.
IC latch circuits are useful in low voltage, low currant applications. When you get into controlling high voltage/high currant applications you get into electro-mechanical latch circuits.
this is what i was looking for 😋 recently i started building an amplifier for my gf and i wanted to build a latch switch in ... instead of mechanical push/latch button .. I found schematics using 555 timer , transistor and rellay , circuit was quite simple , but this is even simpler :) .. and since it involves mosfet, it basically draws miniscule current in comparison to rellay version.. definitely going with this design next time ! many thanx 🙏🏻
Incredible good + useful Electronics Basics tutorial!! I would love to see more of those in the future!
Totally agree! Latching circuits are awesome!
:-)
Great video as always 👍
Thank you very much for this entertaining and educational video. I learned a lot from it. I will try out that circuit out.
Glad you enjoyed it!
@@greatscottlab 🙌
Another place the latch circuit would be handy is for machinery in the event of a power outage. If the power goes out, I don’t want my table saw to restart automatically when the power comes back up.
It would be nice to replace the mechanical switch with a latching circuit. More expensive saws have a magnetic switch that automatically shut off when the power dies.
Love this videos, always great!
Have a think about using TRIACs & SCRs as your switching elements. There is a latching function built in for DC & a very simple capacitor shunt bypass allows the SCR or TRIAC to switch off. These are often overlooked devices with impressive ratings for literally pennies...
Other than the fact you need an additional power IC to power the latch circuit and a isolated driver to drive the interface switch (which is short on supply). Beside that, great video.
Great experiment.
i have tried it with 555 timer ic.
The issue is the circuit required always a healthy power supply.
May be you picked a bipolar 555. There are CMOS versions that take a fraction of the current.
A latched circuit like this would've been useful a few years ago (shortly before a crash I had, lol) for a piece of test equipment I were working on.
I were looking around for one to make that I can then control with a micro-controller to turn itself off when finished to conserve battery for use in the field... I had to make do with another workaround tho.
SR flipflops in integrated circuit form have been around since the 1970's....
@@deang5622 Yes, I know.... I'm on about this more simplified one-button on/off mechanism.
BTW, I ended up using a clocked S/R flipflop IC in the end anyway and then just used the MCU to turn off the supply by resetting the flipflop.
That meant the device stayed on until a delay and the person couldn't just manually turn off the test equipment.
I studied electronics repair in the 1980's after I left active duty and quickly realized the KISS principle, Keep It Simple Stupid, really applies in electronics design. Keeping it simple allows the device to brakedown less and when it does it is easier to repair and get back to the customer.
This is the circuit I've been looking for months.
I tried looking for this type of circuit a few years back, I ended up using another solution.
Funny enough, when I fix up 80's Saab radios, the one model that has a latch circuit is the one that often won't power on until the circuit is recapped or power button repaired. The mechanical volume dial switch models just about always power up
The disadvantage of latch circuits is that they draw small amounts of current which is not much of a problem until the battery goes dead and starts leaking. This is the reason I prefer on-off switches. If you have a battery powered device with a latching on-off switch and don't use it often, take the batteries out. there is less of a worry with a device that does not draw power until it is switched on causing battery leakage. I have a guitar pedal which does not draw power until a cable is plugged into it one day, I opened it up and noticed the battery expiration date was 5 years ago no leakage. I use energizer batteries. I still try to remember to remove batteries if I am not using them however, I do forget sometimes.
People don't realize that these latching circuits are very useful.
Just a few days ago I was looking for a simple way to do one and here you are offering one with your good explanation. Thank you.
Would some time teach how to build a variable square signal generator with a variable duty cycle? to use for inyector cleaning. Using simple devices NOT programable.
Thanks.
My solution to power control is a small circuit/PCB I designed that uses a microcontroller and a 6A high-side MOSFET load switch to control power to any 3.0-5.5VDC circuit. The microcontroller gives the circuit special abilities such as lag/crash detection when used with microcontroller or SBC (e.g., Raspberry Pi) based projects, automatic startup on power-on, automatic restart after crashing, delayed-start/restart, and soft-button power control (tap-on, tap-off, press/hold force-off). I have one of them controlling power to my 3D printer by switching AC mains to the printer's power supply via sold-state relay. It even has a locking USB type-A output connector that's wired to appear to a USB-connected device as a 2.5A charge port, which means it can be used to make custom chargers.
It's been a great little piece of gear, rock solid performance and super-easy to use, and I'd love to mass-produce them but I would have to make a hundred at a time to make the profit/cost ratio worth the time and effort.
Simple but powerful idea⚡😃 This will never wear out and last long
True ;-)
I love one shot- latches, I make bank on service calls swapping them to a mechanical . Keep them coming.
I love your videos. Please tell us you breadboard strategy. I think this is worth a video. What breadboard material you use and your layout strategy that enables you to solder/wire the components. Thanks
Please don’t use this kind of switches or latches for mains voltage purposes. See the comments below (Joop and others). Mains switches shall comply requirements for thermal resistance, fire resistance, clearance distances (as per over voltage category II), failure mode requirements, between others. Component standards and product standards are mandatory in mains related, not an option.
Pretty sure he used a mechanical latch for his lights. AC would fry those transistors he used for the other switch.
Use a relay
Nice going Scott Great!!!!
Thanks!
Be sure to have an R/C across triac type switches that operate anything that would incur a counter emf like a solenoid with a collapsing flux field. The induced voltage from the collapsing flux field will fry the semiconductor type switch.
Learn something nee from your video nice work sir
In a nutshell, every switch has its own applications.
Every switch, every tool, and most (maybe not every) programming features have their own purpose and application. There is never a one size fits all situation, and it is about determining which one is best for the situation.
Many thanks @GS for the interesting, beautifully presented and fast-paced videos. I have found similar circuits on-line but the capacitor sits at the base of the right-side BJT and another, typically higher value resistor charges it through VCC. In your circuit, what limits current flow through the right-side BJT when it is turned on? I can't figure out what would determine the discharge time and what stops the transistor being destroyed? Thanks again....
I was just thinking of a latch circuit and how it operates..wow
Great video ❤️
Great lesson thanks 👍
My pleasure!
Thanks for this video Scott.
The single-button latching circuit seems exactly what I've been looking for for a little battery box I'm currently throwing together.
Quick question, though: What is the time constant for discharging the capacitor when turning the circuit on?
I.e. how fast do I have to let go of the button to avoid immediately turning the circuit off again? ;-)