Another reason to hate "soft touch" power switches - Page 1
Forum section: electronics / projects

author: IDEngineer
author_rank: Super Contributor
timestamp: July 18, 2019, 03:43:17 pm
content: We had a power blip yesterday morning, enough to reset the digital clocks but otherwise not a big deal.Late in the day, I finally made it into the lab... and discovered that things with soft touch power switches had turned themselves on! Most notably for this forum, this included my Rigol DS4000 series scope. It was whirring along, front plastic cover installed so I couldn't visibly tell. I guess now we know why Rigol uses loud fans, as a backup in case their equipment turns itself on and the cover is installed.I HATE soft touch power switches. I understand there are items which actually need to be "lightly" powered on all the time (remote control TV's, etc.) but the majority of soft touch switched things in my life really don't need to be. They would do just as well with a traditional, inexpensive switch that interrupts (at least) the hot side of the mains. The irony here is that the Rigol ALSO has a hard switch which I'd forgotten to turn off last time because it's on the back of the unit, out of sight. It's the worst of both worlds... all the expense of BOTH kinds of power switching, with the hard switch you paid for hidden away so you can easily forget to use it.What is the rationale for defaulting to soft touch power switches these days? Especially on something like an oscilloscope?!? I'd expect the greenies out there to be marching in the streets over all the wasted power (like they do about wall wart chargers) yet I've never heard an environmental peep about it. There must be some overwhelmingly great advantage, so massive that even the greenies are afraid to speak out against them. What am I missing here?

author: JPortici
author_rank: Super Contributor
timestamp: July 18, 2019, 03:51:45 pm
content: Remotely controlled on-off for automated test equipment.Or, at least, this is the reason they gave me when i asked why most of siglent hardware comes with soft buttons.If i need to cut power, all my outlets have switches

author: rsjsouza
author_rank: Super Contributor
timestamp: July 18, 2019, 03:52:08 pm
content: It could be worse... Keysight's E3631x series of Power supplies have no hard switch - both the fan AND the TFT backlight are turned on permanently!I like Rigol featuring both switches - it gives me choice, although I use the soft button more often than not simply due to convenience (it is in the front panel). A hard switch is convenient for the power saving stance but when there's lightning outside, I pull the plug from the outlet!

author: james_s
author_rank: Super Contributor
timestamp: July 18, 2019, 03:53:08 pm
content: As if we needed another reason to hate them. Not sure exactly why everything uses it but I suspect it's a mix of some things requiring a bit more time to cold boot but probably more often it's just what the engineer is familiar with. I suppose it also allows placing a power button on the front panel while allowing the power supply to be placed in a convenient location without mains wiring running all over in the thing.Whatever the case I have my whole workbench on a switched power strip.

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 18, 2019, 03:57:41 pm
content: I'd say that a device equipped with such "soft" on/off button should NOT power on by itself in case of mains power cycling. Sounds like bad design and not something completely inherent to soft power buttons (but obviously with a simple mechanical switch, it can't happen.)Using those has two benefits: usually more convenient for the user as they can be put on front panels. Much easier to deal with especially when you don't have easy access to the back panel. And obviously putting a mains switch on the front panel is usually much more akward from a design POV and not nearly as safe.The other benefit is that it allows the device to be cleanly put in a sleep state when turning it off. Many modern instruments are not unlike computers and switching them off brutally may make them lose their current settings or worse.One easy solution is to have switchable mains rails in your lab.

author: SilverSolder
author_rank: Super Contributor
timestamp: July 18, 2019, 03:59:33 pm
content: Some equipment with IEE-488 ports retains power to the port driver, to avoid loading the bus when powered off. This is one genuine reason for "soft power" on test equipment.

author: Mr. Scram
author_rank: Super Contributor
timestamp: July 18, 2019, 04:01:19 pm
content: Quote from: rsjsouza on July 18, 2019, 03:52:08 pmFor real? I had my eye on one of those, but that's definitely a showstopper.

author: Mr. Scram
author_rank: Super Contributor
timestamp: July 18, 2019, 04:05:26 pm
content: Quote from: SiliconWizard on July 18, 2019, 03:57:41 pmThey solved the mains switch issue decades ago by using pushrods. Shutting down cleanly is a requirement the manufacturers created themselves but which can be solved in other ways.

author: exe
author_rank: Unknown
timestamp: July 18, 2019, 04:08:28 pm
content: I don't like soft switches either. If one needs to power up their equipment remotely, then there is a different alternative: deep sleep mode with wake up by an external interrupt. This gives best of both worlds, imho.

author: ejeffrey
author_rank: Super Contributor
timestamp: July 18, 2019, 04:20:33 pm
content: I think the main reason is cost. An actual mains rated mechanical switch -- especially a front mounted button with a mechanical linkage to the power supply costs a lot more than adding one more membrane switch. It costs more to design and adds to the BOM, tooling, and assembly costs. Not by a huge amount, but when you are counting every penny it is probably hard to justify the mechanical switch.I think all the other claims: remote power up, faster boot times, orderly shutdown, and so on are simply justifications for cost saving or are only really important in a handful of applications.

author: rsjsouza
author_rank: Super Contributor
timestamp: July 18, 2019, 04:21:16 pm
content: Quote from: IDEngineer on July 18, 2019, 03:43:17 pmThis is configurable in the Utility menu.Quote from: SiliconWizard on July 18, 2019, 03:57:41 pmI agree for certain types of equipment, although for servers in remote locations the automatic power on was a lifesaver. Any power glitches were properly logged and the server gracefully recovered its services.Quote from: Mr. Scram on July 18, 2019, 04:01:19 pmOh, please keep your eyes on them. They are wonderful power supplies. I couldn't be more pleased.Quote from: Mr. Scram on July 18, 2019, 04:05:26 pmYes, the pushrods work really fine, although with the years of use they may develop a screeching sound due to metal-on-metal scrubbingI have a few that need some fine grease applied, but I just can't get around to do it.Power switches are critical for embedded OS equipment, as they can allow for the system to perform a proper shutdown. Clunking switches will leave temporary files behind and can cause filesystem corruption. Also, at least on our TV, keeping it on the "sleep" mode allows for a much faster power on (instead of the vaccuum-tube-era power on delay).

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 18, 2019, 04:21:49 pm
content: Quote from: Mr. Scram on July 18, 2019, 04:05:26 pmYeah. That's still a bit cumbersome from a product design POV, especially if the device is pretty crowded, so I guess the soft switches are the easy path and cost a lot less overall. I usually also don't like the "feel" of those pushrod switches much, but I admit that's a completely secondary criterion.Many lab instruments still have both a soft power switch on the front panel AND a mechanical switch on the back.Anyway as we said: switched power strips. Done. So I personally don't care much, but I can understand why some would find that irritating.

author: Mr. Scram
author_rank: Super Contributor
timestamp: July 18, 2019, 04:24:42 pm
content: Even if the graceful shutdown were an excuse not being able to turn off the screen or fan is inexcusable.

author: ejeffrey
author_rank: Super Contributor
timestamp: July 18, 2019, 04:50:11 pm
content: I can see the appeal of having a mechanical rocker switch on the back and a soft power button on the front, but realistically 99% of the time I'm only going to push the front button anyway so the mechanical switch isn't really doing anything for me. I'm sure some people religiously turn off the back power switch in those devices, but I suspect they are a tiny minority.For me a switched power strip is more convenient due to more convenient placement and the ability to power off a whole test setup at once.

author: IDEngineer
author_rank: Super Contributor
timestamp: July 18, 2019, 04:50:20 pm
content: Quote from: ejeffrey on July 18, 2019, 04:20:33 pmI'd agree, except that then your soft-touch startup has to have even MORE mains-rated circuitry behind it to power up the rest of the system under soft-touch control. Something, somewhere, is switching the mains. I've designed a couple soft-touch systems and there wasn't any cost savings. It's hard to match the cost, simplicity, and elegance of a single mains-rated switch.The argument about not running AC power all over the place inside the unit has some merit, but as others have noted truly sensitive equipment solved that decades ago with mechanical devices such as pushrods. (I once had a piece of audio equipment that had a rotary knob on the front with a u-joint shaft system transferring the motion to a switch on a PCB waaaaaay in the back.) But if noise sensitivity is really an issue, just put a single mains switch on the back, such as one of those integrated with the power cord connector (and sometimes fuse too). Sure it's on the back, which won't work for rack mounted gear, but in 90% of applications that would be a very clean solution that nicely captivates the AC to a very small portion of the overall enclosure volume. In truly sensitive equipment, you optimize for performance first - and users of such equipment understand that.

author: IDEngineer
author_rank: Super Contributor
timestamp: July 18, 2019, 04:51:42 pm
content: Quote from: SiliconWizard on July 18, 2019, 04:21:49 pmWhat about the supposed "can't let a hard power switch abruptly interrupt power or you'll corrupt internal data storage?" A power strip would risk thatevery single time.

author: IDEngineer
author_rank: Super Contributor
timestamp: July 18, 2019, 04:55:18 pm
content: Quote from: rsjsouza on July 18, 2019, 04:21:16 pmThen I guess a power strip isn't an option, either, despite many here recommending them as a solution.The solution is to design equipment properly in the first place. There are plenty of products out there with transitory data that manage to not corrupt themselves through proper design. It's easy to know that power has been lost, have a predictable amount of uptime remaining due to latent energy in the power supply, and gracefully clean up before the rails actually die.

author: exe
author_rank: Unknown
timestamp: July 18, 2019, 04:55:59 pm
content: Quote from: IDEngineer on July 18, 2019, 04:51:42 pmJust keep it read-only.

author: ejeffrey
author_rank: Super Contributor
timestamp: July 18, 2019, 04:59:54 pm
content: You can always use the soft-power button to initiate a shutdown and then use the power strip to cut power to the bench once everything is shut down. But data corruption is mostly not a real problem since instruments have to handle power failures without bricking anyway. Even desktop operating systems handle this pretty well these days and the embedded OS used in most instruments are even less likely to have data corruption problems on power loss. Maybe that is an issue with high end instruments like VNAs or high speed oscilloscopes that cost more than a car or a house, but for your standard lab equipment this isn't a problem.

author: IDEngineer
author_rank: Super Contributor
timestamp: July 18, 2019, 05:00:24 pm
content: Quote from: exe on July 18, 2019, 04:55:59 pmSometimes not an option for "embedded OS equipment". However, proper designisan option, where you have a high priority interrupt triggered by loss of AC and you know the rails will survive for XXX milliseconds - during which your firmware's sole job is to stabilize its volatile data. Heck, even spinning disk drives have a version of this where they sense freefall and lock their heads into a safe position that doesn't risk damaging the platter surfaces. And that's in themechanicalrealm.

author: IDEngineer
author_rank: Super Contributor
timestamp: July 18, 2019, 05:02:10 pm
content: Quote from: ejeffrey on July 18, 2019, 04:59:54 pmAnd based on that point, soft touch power switching is unnecessary.

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 18, 2019, 05:04:48 pm
content: Quote from: IDEngineer on July 18, 2019, 04:51:42 pmUh. Just because you use a power strip doesn't mean you shouldn't first switch off the device with its soft button. It just prevents any of the annoyances that were first mentioned, such as having it spuriously restart or having it draw current (however little) when in the soft "off" state when you're not in the lab.

author: IDEngineer
author_rank: Super Contributor
timestamp: July 18, 2019, 05:10:31 pm
content: Quote from: SiliconWizard on July 18, 2019, 05:04:48 pmA traditional hard switch delivers all of those advantages automatically.So far, I'm not hearing much that favors soft touch switches over hard contacts. ATE perhaps, but otherwise not. (I mentioned rack mount but most rack mount equipment isn't power cycled that much anyway, they often don't even HAVE a power switch.)

author: Stray Electron
author_rank: Super Contributor
timestamp: July 18, 2019, 05:35:21 pm
content: I plug everything into outlet strips then I KNOW that it's turned off! This part of the US is prone to a lot of lightning strikes so turning everything completely off is a necessity. Surge protection built into the outlets is an added benefit.

author: IDEngineer
author_rank: Super Contributor
timestamp: July 18, 2019, 05:41:35 pm
content: Quote from: Stray Electron on July 18, 2019, 05:35:21 pmThere's a lot to be said for the power strip concept - including that it completely bypasses any soft switches, in which case the soft switches are completely unnecessary, which was my original point!

author: krayvonk
author_rank: Regular Contributor
timestamp: July 18, 2019, 06:23:15 pm
content: Goes to show making your design fully solid state seems superior but it actually isn't in ways.

author: Bud
author_rank: Super Contributor
timestamp: July 18, 2019, 06:26:09 pm
content: Quote from: ejeffrey on July 18, 2019, 04:50:11 pmThe people who do not cut power using hard switches are the reason i got a beautiful Philips TV ditched by a neighbor after a series of power glitches overnight on the local power line in my area. The TV power supply died, so he had to dump it to the curbe side. It is now serving me well after repair. I always cut the shack power to avoid this type of misfortune with my shack equipment. Guess i am that guy from the "tiny minority" ut so far that practice has served me well.

author: james_s
author_rank: Super Contributor
timestamp: July 18, 2019, 07:35:46 pm
content: Quote from: Mr. Scram on July 18, 2019, 04:24:42 pmCan we confirm that they all behave this way? Because if I encountered this I would assume it was a defect, shorted transistor driving that power rail for example.

author: rsjsouza
author_rank: Super Contributor
timestamp: July 18, 2019, 09:15:15 pm
content: Quote from: Mr. Scram on July 18, 2019, 04:24:42 pmI agree this is shameful. However, it doesn't detract from where it matters the most: when the power supply is actually turned on.Quote from: james_s on July 18, 2019, 07:35:46 pmThere were several EEVBloggers that sent their units back to Keysight for a recall (myself included) and the exchanged units presented the same behaviour.

author: magic
author_rank: Super Contributor
timestamp: July 18, 2019, 09:22:55 pm
content: Quote from: SiliconWizard on July 18, 2019, 03:57:41 pmThey probably wanted to make it power up instantly when it is turned on with the mechanical switch. Otherwise somebody would inevitably return it as DOA

author: IDEngineer
author_rank: Super Contributor
timestamp: July 18, 2019, 09:38:37 pm
content: Quote from: magic on July 18, 2019, 09:22:55 pm...in which case, what is the value of a soft touch power switch?If the hard switch actually switches the mains, then it (should be) like (un)plugging the cord. On the other hand, if the unit cantell the differencebetween 1) being plugged in with the hard switch closed, and 2) turning on the hard switch when the cord is already plugged in, then the hard switch is AFTER some active circuitry - a bizarre "design" that few would ever expect. Ask yourself... if there's a hard switch, would you think that turning it off would still leave some portion of the unit powered by mains?

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 18, 2019, 09:41:41 pm
content: Well as for me, again I don't really mind those soft power buttons. As long as they are implemented correctly (which granted is not always the case).What infuriates me a lot more, with modern equipment, is those that take AGES to start ("boot"). Fucking annoying if you ask me.

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 18, 2019, 09:57:05 pm
content: Quote from: magic on July 18, 2019, 09:22:55 pmWell, if any engineer or technician was dumb enough not to even think of trying to press the power button on the front panel before declaring the device dead, I'd be tempted to think that they would deserve getting nothing but DOA equipment anyway...And if there were potentially enough of them to warrant such a design decision, then I'd be definitely worried about the future of the tech professions.

author: IDEngineer
author_rank: Super Contributor
timestamp: July 18, 2019, 09:57:41 pm
content: Quote from: SiliconWizard on July 18, 2019, 09:41:41 pmGranted, but my question is: What value do they ADD that justifies their complexity, cost, and the added downside of often being implemented INcorrectly? They seem to be the default power switch these days, but except for a few special cases there doesn't seem to be an advantage that justifies them. You say "I don't really mind those soft power buttons" but I bet you'd be just as happy with a hard switch.

author: tautech
author_rank: Super Contributor
timestamp: July 18, 2019, 10:06:47 pm
content: Quote from: IDEngineer on July 18, 2019, 09:57:41 pmThey ADD the ability to have a powerful OS that permits incorporation of complex features into an instrument and that OS needs be shut down gracefully to retain settings.Most that have soft key power buttons also have the feature to set what happens after a power failure as has already been pointed out to you.Apparently you had changed from default power behavior so no wonder your DSO restarted after a power failure.

author: IDEngineer
author_rank: Super Contributor
timestamp: July 18, 2019, 10:14:25 pm
content: Quote from: tautech on July 18, 2019, 10:06:47 pmSure, but as has already been noted in this thread, embedded systems commonly handle loss of power. A soft touch power switch does not protect from AC interruption, and most equipment doesn't say "Must be used with suitable UPS".Most folks here would consider T&M equipment that bricked due to AC loss to be a terrible design. Thus they must design for that, in which case the soft touch switch adds nothing.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: July 18, 2019, 10:15:05 pm
content: My Tektronix 547 wouldn't even turn on with a direct lightning strike!

author: magic
author_rank: Super Contributor
timestamp: July 18, 2019, 10:29:46 pm
content: Quote from: IDEngineer on July 18, 2019, 09:38:37 pmThe value of a soft button is that it can be cheaply and conveniently placed on the front panel among other low voltage stuff.The value of a true switch at the rear of the unit might be that it is mandatory for devices which aren't insulation class II rated or something like that, I'm not familiar with the rules myself but I think I've heard it's a requirement in the EU these days.Quote from: SiliconWizard on July 18, 2019, 09:57:05 pmThese are scopes for kidsBesides, I can imagine some oldschool tech turning the switch on, cursing Rigol for having placed in at the rear and not realizing that there is another button to be pressed.

author: tautech
author_rank: Super Contributor
timestamp: July 18, 2019, 10:32:34 pm
content: Quote from: IDEngineer on July 18, 2019, 10:14:25 pmNope, you're missing something.Loss of power without the proper shutdown only loses the users last settings like if you were using some specific settings for triggering and channel settings.Instruments default to particular settings for you then to need to reset to what you were using before.Nuthing at all like turning it into a brick..........but, for loss of power while doing a firmware update, that's an entirely different matter and a risk that's warned about in firmware upgrade instructions.Still that's recoverable if the manufacturer permits it with the correct external SW input.Typically instruments with dumber OS'es have hard switches and ones with complex OS'es use soft switching.....yes, it's that simple !

author: IDEngineer
author_rank: Super Contributor
timestamp: July 18, 2019, 10:51:42 pm
content: Quote from: tautech on July 18, 2019, 10:32:34 pmI'm not talking about firmware upgrades, which is a special case.As noted earlier herein:QuoteIt is entirely possible to design a system with a hard switch that saves its configuration during powerdown, because powerdown would be no different than loss of AC. This is actually a better design, because the same procedure is used whether the shutdown is intentional or accidental. The results when the device powers back up are the same in either case, and (again) no soft touch power switch is required. Reliable, predictable behavior regardless of why the unit shut down.

author: tooki
author_rank: Super Contributor
timestamp: July 18, 2019, 11:22:20 pm
content: The main reason, beside remote control, that I can think of for soft power is to allow for proper shutdown. I guess I’m familiar with this from early Macs: on many early models, they had only hard power, so the Shutdown command would shut down the OS but then leave you at a “It is now safe to turn off your Macintosh” message. Soft power models never showed that message, but instead behaved like modern computers that simply turn off when done shutting down the OS. I suppose that in scopes that run fairly complex embedded OSes that don’t like being shut down ungracefully, thus could be a reason for soft power. Another (probably irrelevant to test gear) is the ability for a RTC to perform scheduled power up and down.I also wonder whether various countries’ electrical regulatory standards come into play. While studying the service manuals for various Sony hi-fi components I have (all from late 90s-early 00s) which have real hard power switches, I noticed that some versions of the same model used the front panel switch to cut the incoming AC power, while others use the same switch to cut the output of the mains transformers! For example, my European devices all cut the AC, while the US and Australia versions would have cut the secondary. Or are there other explanations for doing this? I can’t imagine that it saves any money. (In one tape deck, for example, some versions use an SPST switch to cut the mains, while other versions use a DPDT switch, using one pole to cut the VFD filament power, and the other to pull alternate logic signals low to, I suppose, tell the MCU to “turn off” the deck. To the best of my knowledge, neither version supported power on/off or standby by remote control.)

author: IDEngineer
author_rank: Super Contributor
timestamp: July 18, 2019, 11:46:49 pm
content: Quote from: tooki on July 18, 2019, 11:22:20 pmWe're all repeating the same thing:* Soft switches can be used to gracefully shut down a low-end product where they don't bother to detect unintentional loss of AC.* But it's not necessary to use a soft switch to achieve proper shutdown. If AC power loss can be gracefully tolerated, then a soft switch adds literally nothing except cost and complexity.

author: tautech
author_rank: Super Contributor
timestamp: July 19, 2019, 12:40:41 am
content: Quote from: IDEngineer on July 18, 2019, 11:46:49 pmAnd there ^ you have it, hard switch Windoze OS'es and see how you get on.At least Linux OS'es will tolerate it despite the risk of losing settings.Each to their own....it's just part of the idiosyncrasies of any equipment.

author: IDEngineer
author_rank: Super Contributor
timestamp: July 19, 2019, 12:58:56 am
content: Quote from: tautech on July 19, 2019, 12:40:41 amWindows isn't an embedded system. The motherboard/BIOS spec doesn't include AC power loss hardware so stock Windows doesn't support such functionality.An embedded system, like that in a scope or other dedicated piece of hardware, can (and quality ones do!) contain AC power loss detection precisely because they want to treat their customers properly. They have tens to hundreds of milliseconds to store data before the supply rails drop off. That same approach works whether the AC power went away due to the power company, or due to the user turning off a hard switch.I'm surprised some folks are defending soft switches. As this thread has revealed, in all but a few applications they are a crutch for lazy engineering. If your scope loses config data (or faults) like Windows when you cut its power, you've exposed a design deficiency. Maybe it's acceptable at that price point, but don't claim it's anything but a compromise because it's easily possible toavoidthat problem without relying on magic or unobtainium.QuoteBut it doesn'thaveto be. It's just lazy engineering.

author: rsjsouza
author_rank: Super Contributor
timestamp: July 19, 2019, 02:20:59 am
content: I don't think it is lazy engineering - the main reason I can see is to be quick enough to have application data be written to the non-volatile media before the power is off. The reason the data is in RAM is most probably due to running performance - in the world of ultra fast SSDs, RAM is still the absolute performance king.This is also not a cost cutting scenario, as the highest-end oscilloscopes are Windows or other HLOS based, as well as the vast number of PCs of all price points in existence today without a clunking switch.The systems I saw running embedded Linux that did not have issues with a clunking switch were running entirely from RAM - simpler systems that still took a while to boot to load from flash to RAM (more than one minute).I don't think the soft switch is an issue per se, especially in the light of the benefits it can bring to cater to complex OSes and therefore better featured and better performing equipment. Besides, if designed properly the power consumption is very minimal and with decent isolation (using latching relays, for example).

author: IDEngineer
author_rank: Super Contributor
timestamp: July 19, 2019, 02:52:22 am
content: Quote from: rsjsouza on July 19, 2019, 02:20:59 amNo question there. But the discussion has been about storing user preferences, front panel setups, etc. to nonvolatile memory. Not storing megabytes of captured, digitized data. The former would be measured in hundreds of bytes, not megabytes, and you can easily write that amount of data to EEPROM or flash in the time it takes for the rails to taper off. So unless the argument is "We're preserving all of your captured image data", there's simply no reason that an AC power loss detection circuit that drives a hardware interrupt can't do double duty and protect against both unplugged line cords and turned-off hard switches.QuoteSee above. The "better features" and "better performance" would have to be megabytes of data, or else the argument doesn't hold. And that begs the question: How do they deliver these "betters" when AC is unexpectedly lost? Think flipped switch, electrical company glitch, tripped-over cord, etc. Do they just write that off, sorry for you dear user, tough luck?(True story: I was working on a very early Linux system years ago when something rolled off the back of the table and of all the places it could have fallen, it fell right on the switch on the power strip. Trashed the hard drive partition so badly I had to reinstall the OS. That's when I started taping across power strip switches with duct tape. You just never know when AC will fail you, which is why a properly designed piece of expensive T&M equipment should protect against at least the loss of basic volatile data. I don't expect megabytes to be magically preserved, but loss of AC is just too much of a risk to ignore. And once you've solved that problem, a hard switch is precisely zero different and can enjoy the same benefits.)

author: vk6zgo
author_rank: Super Contributor
timestamp: July 19, 2019, 05:16:01 am
content: Of course, if you run your gear 24/7 in "awake" mode, you may be presented with the opposite problem, where your SMPS "start up" circuit has failed.Only when you have a mains failure, do you notice this.------great fun being stuck with several devices which won't turn back on.Even more off topic, but a good story, so being an O.F., I will tell you anyway:-Back in the day, I was tasked to lead a team automating a TV Transmitter site which used Tx which had never been designed for such service.With a lot of workarounds, cut & try, etc, we got together a system which was effectively "a Tech in a box", using a Programmable Logic Controller & a whole raft of electromechanical interfaces.This, when it received the right signal from the Studio (the presence or absense of vertical syncs) would, in turn, switch on the tube filaments, wait 5 minutes, then apply the HT.At closedown, it would perform the opposite procedure.(it also did a lot of other stuff)All good, but if there was a power loss, then the emergency power plant (EPP) took over, we needed to "truncate" the procedure to get back on air as quickly as possible.To do this, we needed an input to the PLC to indicate the loss of power.(It could detect this itself, but didn't provide it as an input).This site used -24v fed aound the building to do various things, & this was normally provided by a Mains operated power supply.In a power failure, the 24 volt EPP starting battery would take over via some "steering diodes".We blithely connected our PLC input to the "unprotected" side of the diodes, so that Mains loss should cause the loss of -24v, & trigger the fast TX restartSeveral "simulations" of a Mains fail worked OK, so the system was put into service.The first weekend, I was callef out for a transmitter failure.I was presented with the spectacle of both sound transmitters up ok, but both vision Tx with HT on & no filaments.( needless to say, this is an undesirable condition).It turned put that the large electrolytics on the supply kept the DC voltage applied to the PLC input up long enough for the normal startup procedure to occur, but without the initial "fils on" step.This was quickly "bodged up" by bulding an unfiltered DC supply in a handy plastic box, plugging it into the nearest power point with a "don't turn off!" sign attached, pending the provision of a better alternative.The only relevance this has to the thread is that it is incredibly easy to set up a system where the unintended consequences are so weird, that they are overlooked.We assumed that the worst case result of this input not working being the controller just reverting to its normal start up sequence, rather than what actually happened.All the other functions worked perfectly.

author: Mr. Scram
author_rank: Super Contributor
timestamp: July 19, 2019, 06:13:30 am
content: Quote from: rsjsouza on July 18, 2019, 09:15:15 pmUnless you're running a factory where equipment is up 24/7, I'd argue the off state is as relevant as the on state. Even if you're not looking at it while the device is in it. I can't confirm or deny this is intended behaviour, as I don't own one of these power supplies.

author: Mr. Scram
author_rank: Super Contributor
timestamp: July 19, 2019, 06:18:30 am
content: Quote from: tautech on July 18, 2019, 10:06:47 pmThat's just fixing one problem with another. Build a more robust OS or hardware and you'll never have to fix the problem of things going corrupt with a power failure in the first place. We already established that power failures do occur without mains switches, so not having an OS robust enough to survive an outage is already shoddy engineering.

author: Mr. Scram
author_rank: Super Contributor
timestamp: July 19, 2019, 06:39:03 am
content: Quote from: rsjsouza on July 19, 2019, 02:20:59 amImplementing complex OSs with a hard switch is a doable engineering problem. Implementing soft switches with the associated downsides like power consumption and apparently costs seem to be lazy engineering. It's strange people are content to give up core features when they're offset with some shiny gimmicks. It can do everything except for things equipment did 50 years ago.

author: soldar
author_rank: Super Contributor
timestamp: July 19, 2019, 07:13:08 am
content: I still have an old CRT TV that after a power outage turns on with audio volume at whatever level it was set. I once came back from a long trip and the neighbors were surprised to hear I had been gone because the TV had been blasting away for days. Now I remember to turn the volume down if I am leaving for more than a few days.I have mentioned in another thread that I have a big multimeter that has the only switch in the back, like computers, where it is unreachable with the instrument mounted in rack or shelves. I put an inline switch in the power cord. Which is still a pain.

author: exe
author_rank: Unknown
timestamp: July 19, 2019, 08:15:09 am
content: Huh, my micsig oscilloscope turns on when I... turn off the bench (the scope has internal battery). It does so with a delay and it cannot be powered off before it finishes booting. It also does it inconsistently, like in 50% of the time. Just unplugging the oscilloscope from the power brick doesn't do anything, but unpluging the brick from mains triggers power on. So, every time I do something with a scope I have to think what power state it will be in the end. I ended up using it from battery only. Horrible design...

author: rsjsouza
author_rank: Super Contributor
timestamp: July 19, 2019, 10:43:31 am
content: Quote from: IDEngineer on July 19, 2019, 02:52:22 amThe discussion has been about what the soft button ADDs to your system. My point is they add more predictability to a system that can benefit from still having available power to guarantee extra reliability during critical operations by means of a controlled shutdown. It could also improve bootstrap performance by keeping the system in some sort of suspended or sleep mode state. Just picture a high end oscilloscope with a HLOS and it becomes much more difficult to move away from the soft switch. It is not impossible if you are rolling your own OS or use one of the expensive real-time HLOS around (VxWorks, QNX, etc), but much more difficult if you have a commercial HLOS running on the machine. Again, the soft switch can bring an added value if one desires a commercial HLOS on such equipment.Specific to the user preferences, etc., small amounts of data like these can be written to flash directly in an unbuffered operation. Even still, the internal RTOS or HLOS may need to queue this operation before it has time to properly finish this operation. Being carefully planned, the most critical operations before a powerdown (the ones that can potentially corrupt the system) must be tied to a NMI to avoid interrupt priority queuing, but perhaps other less critical operations (such as user settings or preferences) may or may not be fully completed before the power is completely lost - manifesting themselves as operations not saved at the next power up (a nuisance). Now, queue a power loss in the shape of a user-operated clunking switch, which happens orders of magnitude more often than an actual power loss: the probability of the nuisance errors happening is magnified.Is it impossible to make a system completely bullet proof? No, and I mentioned my experience in my previous post, but the limitations there are a tradeoff that I am willing to have.Quote from: IDEngineer on July 19, 2019, 02:52:22 amDepending on the complexity of the system, that may not be the case. Just picture a high end oscilloscope with a HLOS and it becomes much more difficult to move away from the soft switch. It is not impossible if you are rolling your own OS or use one of the expensive real-time HLOS around (VxWorks, QNX, etc), but much more difficult if you have a commercial HLOS running on the machine. Again, it is a tradeoff between added functionality and implementation details.Quote from: Mr. Scram on July 19, 2019, 06:13:30 am??!?? Really ??!!??Each to its own... To me a power supply in the OFF state is almost completely irrelevant as it does not fulfill its main function, which is to power stuff around. At power off, the only function it does is to look good in my bench and impress my technically inclined friends. For that, I don't think I can fault it either - it looks really good!Quote from: Mr. Scram on July 19, 2019, 06:39:03 amI didn't say it isn't. See above. But to me a clunking switch is not a "core feature" but a small detail in the overall system. Again, each to its own.

author: Mr. Scram
author_rank: Super Contributor
timestamp: July 19, 2019, 10:47:46 am
content: Quote from: rsjsouza on July 19, 2019, 10:43:31 amThe ability to turn off equipment so that it's not consuming power, heating up the room, wearing out the equipment itself and not a potential fire hazard is definitely a core feature. It's the baseline of what can be reasonably expected. Can you imagine not being able to turn off your car?

author: exe
author_rank: Unknown
timestamp: July 19, 2019, 11:00:36 am
content: Same here on off-"feature". Most my T&M equipment used less than 1% of the time, except lab power supplies and my laptop.I cut mains off when I don't use my lab, I don't want my house to be burned by a malfunctioning device (I have about twenty devices plugged in the lab, some of them second-hand and old).

author: Richard Crowley
author_rank: Super Contributor
timestamp: July 19, 2019, 11:26:44 am
content: When I was managing the E-test lab (on-wafer evaluation of test-dice during process development) we had a problem with mains power interruptions for a period. The hits were pretty short so that most equipment would keep running, although after scrambling the operation.After many very valuable test wafers were ruined, I got a bunch of power contactors and installed one in each equipment rack. So that power for the rack was provided through the contactor, but it would drop-out with any power interruption. At the local surplus store, I found some nice green N.O. "START" buttons, and red N.C. "STOP" buttons. and built them into a nice 1RU panel at the top of each rack.That gave us the opportunity to go around to each automated test station and re-start it properly vs. letting the zombie equipment to go on a rampage.

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 19, 2019, 12:45:51 pm
content: Quote from: IDEngineer on July 18, 2019, 09:57:41 pmWell, as for the "value", I think we already covered that. Additionally, they add a more "modern" look and feel. You are of course entitled to personally find those values are of no value to you.As I said earlier though, I think you're mistaken in thinking they add complexity and cost. In many cases, in modern equipment, I'd say they are pretty cheap to add, and that they are actually much simpler overall than having to deal with proper handling of sudden power-on and power-off, not just for the graceful shutdown cases, but also any time a specific power supply sequencing is required, and other reasons. Anything that is less expensive/or more flexible to deal with in software than purely in hardware.Depending on the implementation, upon soft shutdown, they can do as little as putting the whole instrument in a "sleep" mode (thus not necessarily shutting down the main power supplies but merely shutting down everything that was already meant to be enabled/disabled by software and then put the display(s) and CPU(s) to sleep as well. They can additionally partially shut the main power supplies down (usually only partially). This last thing doesn't cost anything much either these days. Many DC/DC power modules used in those instruments already contain control signals to shut the PS down (as with computer PSUs), so the cost is practically nothing.Quote from: IDEngineer on July 18, 2019, 09:57:41 pmWell, this is a good point. But a "hard" power switch can be implemented incorrectly in many ways as well due to reasons exposed before...Again, I think most manufacturers will favor this solution for several reasons, but the main one being that everything that depends more on software than hardware is considered much more flexible and much easier to fix if there are bugs, so in that respect, that's more of a comfortable option for the manufacturer than for the user.I personally don't mind much, but I think there should be some sense of proportion when designing a lab instrument. Whereas I expect a modern scope to be much like a dedicated computer, thus I expect it to function much like one (except I still expect it to boot faster than a typical computer!), for a simple lab power supply, I would find that silly.Now when a manufacturer has a whole range of instruments, that still makes sense to use a common OS, for instance, and common subsystems in all of them when possible. So again what's a benefit for the manufacturer is not necessarily a direct benefit for the users.

author: IDEngineer
author_rank: Super Contributor
timestamp: July 19, 2019, 04:04:38 pm
content: Quote from: SiliconWizard on July 19, 2019, 12:45:51 pmHere's how it pencils out:1) Some devices don't care about power loss. There is no timing requirement to losing power, regardless of reason. They need take no special action to handle loss of power.2) The remaining devices do care about power loss, and must design to accommodate it, again regardless of reason (intentional or unintentional).Device type (1) can use either type of power switch because it literally doesn't matter. Device type (2) MUST handle power loss because it can occur for lots of reasons unrelated to the power switch - and once it must handle unexpected power loss, it can automatically handle a hard switch because that is no different from a power company event.The moment someone suggests there is a "middle ground", where a soft switch is needed because the OS "needs to do something special when power is lost", we're right back at #2 above: What happens when power is lost at the wall? The device can either accommodate that (in which case it's type 1) or it can't (in which case it's type 2), and in both cases a properly designed instrument does not require a soft switch.That leaves one middle ground: An IMproperly designed instrument that expects power to "play nice" 100% of the time, where theyassume power is never lost unexpectedly, and so the "Engineers" on that project leave a gaping hole that causes inconvenience (or worse) when power is nevertheless lost without warning. I would consider such a "middle ground" to be a broken design because a properly designed instrument should anticipate, and gracefully handle, predictable events like power loss. And those that do immediately put themselves into type 2 above, where a hard switch works as well as a soft one.QuoteThat's precisely the point: Graceful handling of power loss IS a software event. It is software which is notified that power has been lost, and reacts by saving important non-volatile information. Yes, there's a hardware cost for the AC-loss detection circuitry but that's vanishingly small in any modern instrument's BOM budget, and once that's in place you get exactly what you described: "less expensive/or more flexible to deal with in software", to the extent that if it's later realized that some important piece of data wasn't being preserved that can be corrected with a firmware update.Bottom line: Power loss either matters or it doesn't. If it does, you have to handle the unexpected loss of power anyway. And once you've done that, a soft switch doesn't add anything (the OS is already getting notified of power loss, so there's no additional information conveyed by actuating a soft switch).

author: Dundarave
author_rank: Regular Contributor
timestamp: July 19, 2019, 04:44:56 pm
content: Back in the day, one had to “gracefully” shut down gear so that cached data would be written out to slower permanent storage, i.e. hard drives, etc. Caching, and thus the need to be careful about blowing away the cache before it get written, is essentially a hack to mitigate read/write wait times.Given that almost everything is now solid-state and the data speeds are so fast, what kind of test gear would still require such a process? If a scope can save giga-samples per second in real time, surely it can save your trace color selection in the time between “Ok” and when the power goes out...

author: rrinker
author_rank: Super Contributor
timestamp: July 19, 2019, 08:51:58 pm
content: I do not like leaving ANYTHING on when I am not there - so everything on my bench is plugged in to a power strip that has a nice handy remote on/off hard switch with a pilot light, which I have mounted up under the corner next to where my socket is for wrist straps.For my basement/model train room, I have all the wall outlets where everything plugs in to controlled by a central switch to shut off the whole thing when I am not there.About the only thing I leave running 24/7 is my main desktop computer and my server, and even those get shut down when I am away for any extended period of time like I am now (no worries, I posted about being away on another forum and someone mentioned security. Well, I have two of the most evil, vicious guard Pugs ever known, plus my house is not empty just because I happen to be gone).(the Pugs are so vicious they might trip you in attempting to be the first to get scratches and treats even if you are a complete stranger)

author: ratatax
author_rank: Regular Contributor
timestamp: July 20, 2019, 01:30:54 pm
content: Soft power on may be a way to save cost and make engineering easier even if it needs some additional components to switch the mains.For the product I design I looked for big clunky mains switches, they are costly and a nightmare to integrate into a product, you have to attach them in some way usually it's not easy if they are not panel mount, the button cap is also a hassle since no switch have a standard plug, you'll have to mold your own or rely on the manufacturer's ones which usually provide very poor choices (shapes, colours). You also have to bring the mains close to the front panel with cables, or use a complicated lever system.In terms of mechanical engineering, a simple press button like the others on the front panel is so much easier, and of course it has all the benefits you mentionned like saving data before shutting down etc.If it's well implemented I don't see the problem, a well designed circuit should draw only a few milliamps