Author Topic: Another reason to hate "soft touch" power switches  (Read 6999 times)

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Offline krayvonk

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Re: Another reason to hate "soft touch" power switches
« Reply #25 on: July 18, 2019, 06:23:15 pm »
Goes to show making your design fully solid state seems superior but it actually isn't in ways.
 

Offline Bud

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Re: Another reason to hate "soft touch" power switches
« Reply #26 on: July 18, 2019, 06:26:09 pm »
  I'm sure some people religiously turn off the back power switch in those devices, but I suspect they are a tiny minority.
The 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.
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Offline james_s

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Re: Another reason to hate "soft touch" power switches
« Reply #27 on: July 18, 2019, 07:35:46 pm »
Even if the graceful shutdown were an excuse not being able to turn off the screen or fan is inexcusable.

Can 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.
 
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Offline rsjsouza

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Re: Another reason to hate "soft touch" power switches
« Reply #28 on: July 18, 2019, 09:15:15 pm »
Even if the graceful shutdown were an excuse not being able to turn off the screen or fan is inexcusable.
I agree this is shameful. However, it doesn't detract from where it matters the most: when the power supply is actually turned on.

Can 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.
There were several EEVBloggers that sent their units back to Keysight for a recall (myself included) and the exchanged units presented the same behaviour.
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Offline magic

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Re: Another reason to hate "soft touch" power switches
« Reply #29 on: July 18, 2019, 09:22:55 pm »
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.)
They 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 :P
 

Offline IDEngineerTopic starter

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Re: Another reason to hate "soft touch" power switches
« Reply #30 on: July 18, 2019, 09:38:37 pm »
They probably wanted to make it power up instantly when it is turned on with the mechanical switch.
...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 can tell the difference between 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?
 

Online SiliconWizard

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Re: Another reason to hate "soft touch" power switches
« Reply #31 on: July 18, 2019, 09:41:41 pm »
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.
 

Online SiliconWizard

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Re: Another reason to hate "soft touch" power switches
« Reply #32 on: July 18, 2019, 09:57:05 pm »
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.)
They 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 :P

Well, 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... :-DD

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. ;D
 

Offline IDEngineerTopic starter

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Re: Another reason to hate "soft touch" power switches
« Reply #33 on: July 18, 2019, 09:57:41 pm »
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).
Granted, 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.
 

Online tautech

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Re: Another reason to hate "soft touch" power switches
« Reply #34 on: July 18, 2019, 10:06:47 pm »
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).
Granted, 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.
They 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.
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Offline IDEngineerTopic starter

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Re: Another reason to hate "soft touch" power switches
« Reply #35 on: July 18, 2019, 10:14:25 pm »
They 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.
Sure, 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.
 

Offline Alex Eisenhut

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Re: Another reason to hate "soft touch" power switches
« Reply #36 on: July 18, 2019, 10:15:05 pm »
My Tektronix 547 wouldn't even turn on with a direct lightning strike!
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Offline magic

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Re: Another reason to hate "soft touch" power switches
« Reply #37 on: July 18, 2019, 10:29:46 pm »
They probably wanted to make it power up instantly when it is turned on with the mechanical switch.
...in which case, what is the value of a soft touch power switch?
The 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.

Well, 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... :-DD
These are scopes for kids :P
Besides, 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.
« Last Edit: July 18, 2019, 10:35:17 pm by magic »
 

Online tautech

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Re: Another reason to hate "soft touch" power switches
« Reply #38 on: July 18, 2019, 10:32:34 pm »
They 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.
Sure, 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.
Nope, 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 !
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Offline IDEngineerTopic starter

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Re: Another reason to hate "soft touch" power switches
« Reply #39 on: July 18, 2019, 10:51:42 pm »
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.
I'm not talking about firmware upgrades, which is a special case.

As noted earlier herein:

Quote
However, proper design is an 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 the mechanical realm.

It 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.
 

Offline tooki

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Re: Another reason to hate "soft touch" power switches
« Reply #40 on: July 18, 2019, 11:22:20 pm »
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.)
 

Offline IDEngineerTopic starter

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Re: Another reason to hate "soft touch" power switches
« Reply #41 on: July 18, 2019, 11:46:49 pm »
The main reason, beside remote control, that I can think of for soft power is to allow for proper shutdown.
We'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.
« Last Edit: July 18, 2019, 11:58:25 pm by IDEngineer »
 

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Re: Another reason to hate "soft touch" power switches
« Reply #42 on: July 19, 2019, 12:40:41 am »
The main reason, beside remote control, that I can think of for soft power is to allow for proper shutdown.
We'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.
And 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.
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Offline IDEngineerTopic starter

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Re: Another reason to hate "soft touch" power switches
« Reply #43 on: July 19, 2019, 12:58:56 am »
And there ^ you have it, hard switch Windoze OS'es and see how you get on.
Windows 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 to avoid that problem without relying on magic or unobtainium.

Quote
it's just part of the idiosyncrasies of any equipment
But it doesn't have to be. It's just lazy engineering.
« Last Edit: July 19, 2019, 01:06:19 am by IDEngineer »
 

Offline rsjsouza

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Re: Another reason to hate "soft touch" power switches
« Reply #44 on: July 19, 2019, 02:20:59 am »
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).
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Offline IDEngineerTopic starter

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Re: Another reason to hate "soft touch" power switches
« Reply #45 on: July 19, 2019, 02:52:22 am »
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.
No 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.

Quote
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.
See 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.)
 

Offline vk6zgo

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Re: Another reason to hate "soft touch" power switches
« Reply #46 on: July 19, 2019, 05:16:01 am »
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 restart

Several "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.



« Last Edit: July 19, 2019, 08:27:25 am by vk6zgo »
 

Offline Mr. Scram

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Re: Another reason to hate "soft touch" power switches
« Reply #47 on: July 19, 2019, 06:13:30 am »
I agree this is shameful. However, it doesn't detract from where it matters the most: when the power supply is actually turned on.

There were several EEVBloggers that sent their units back to Keysight for a recall (myself included) and the exchanged units presented the same behaviour.
Unless 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.
 

Offline Mr. Scram

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Re: Another reason to hate "soft touch" power switches
« Reply #48 on: July 19, 2019, 06:18:30 am »
They 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.
That'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.
 

Offline Mr. Scram

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Re: Another reason to hate "soft touch" power switches
« Reply #49 on: July 19, 2019, 06:39:03 am »
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).
Implementing 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.  :palm:
 


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