Author Topic: Another reason to hate "soft touch" power switches  (Read 7003 times)

0 Members and 1 Guest are viewing this topic.

Offline IDEngineerTopic starter

  • Super Contributor
  • ***
  • Posts: 1950
  • Country: us
Another reason to hate "soft touch" power switches
« on: July 18, 2019, 03:43:17 pm »
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.  :o

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?
« Last Edit: July 18, 2019, 03:46:09 pm by IDEngineer »
 

Online JPortici

  • Super Contributor
  • ***
  • Posts: 3573
  • Country: it
Re: Another reason to hate "soft touch" power switches
« Reply #1 on: July 18, 2019, 03:51:45 pm »
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
 

Offline rsjsouza

  • Super Contributor
  • ***
  • Posts: 6105
  • Country: us
  • Eternally curious
    • Vbe - vídeo blog eletrônico
Re: Another reason to hate "soft touch" power switches
« Reply #2 on: July 18, 2019, 03:52:08 pm »
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!  :o
Vbe - vídeo blog eletrônico http://videos.vbeletronico.com

Oh, the "whys" of the datasheets... The information is there not to be an axiomatic truth, but instead each speck of data must be slowly inhaled while carefully performing a deep search inside oneself to find the true metaphysical sense...
 
The following users thanked this post: Mr. Scram

Offline james_s

  • Super Contributor
  • ***
  • Posts: 21611
  • Country: us
Re: Another reason to hate "soft touch" power switches
« Reply #3 on: July 18, 2019, 03:53:08 pm »
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.
 

Online SiliconWizard

  • Super Contributor
  • ***
  • Posts: 15797
  • Country: fr
Re: Another reason to hate "soft touch" power switches
« Reply #4 on: July 18, 2019, 03:57:41 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.)

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.
 

Offline SilverSolder

  • Super Contributor
  • ***
  • Posts: 6126
  • Country: 00
Re: Another reason to hate "soft touch" power switches
« Reply #5 on: July 18, 2019, 03:59:33 pm »
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.
 

Offline Mr. Scram

  • Super Contributor
  • ***
  • Posts: 9821
  • Country: 00
  • Display aficionado
Re: Another reason to hate "soft touch" power switches
« Reply #6 on: July 18, 2019, 04:01:19 pm »
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!  :o
For real? I had my eye on one of those, but that's definitely a showstopper.
 

Offline Mr. Scram

  • Super Contributor
  • ***
  • Posts: 9821
  • Country: 00
  • Display aficionado
Re: Another reason to hate "soft touch" power switches
« Reply #7 on: July 18, 2019, 04:05:26 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.)

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.
They 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.
 

Offline exe

  • Supporter
  • ****
  • Posts: 2647
  • Country: nl
  • self-educated hobbyist
Re: Another reason to hate "soft touch" power switches
« Reply #8 on: July 18, 2019, 04:08:28 pm »
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.
 

Offline ejeffrey

  • Super Contributor
  • ***
  • Posts: 4033
  • Country: us
Re: Another reason to hate "soft touch" power switches
« Reply #9 on: July 18, 2019, 04:20:33 pm »
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.
 

Offline rsjsouza

  • Super Contributor
  • ***
  • Posts: 6105
  • Country: us
  • Eternally curious
    • Vbe - vídeo blog eletrônico
Re: Another reason to hate "soft touch" power switches
« Reply #10 on: July 18, 2019, 04:21:16 pm »
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.
This is configurable in the Utility menu.
788259-0

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.)
I 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.

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! (...)
For real? I had my eye on one of those, but that's definitely a showstopper.
Oh, please keep your eyes on them. They are wonderful power supplies. I couldn't be more pleased.  :-+

They 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.
Yes, the pushrods work really fine, although with the years of use they may develop a screeching sound due to metal-on-metal scrubbing  :-DD I 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 :palm:).
« Last Edit: July 18, 2019, 04:23:10 pm by rsjsouza »
Vbe - vídeo blog eletrônico http://videos.vbeletronico.com

Oh, the "whys" of the datasheets... The information is there not to be an axiomatic truth, but instead each speck of data must be slowly inhaled while carefully performing a deep search inside oneself to find the true metaphysical sense...
 

Online SiliconWizard

  • Super Contributor
  • ***
  • Posts: 15797
  • Country: fr
Re: Another reason to hate "soft touch" power switches
« Reply #11 on: July 18, 2019, 04:21:49 pm »
They solved the mains switch issue decades ago by using pushrods.

Yeah. 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.

 

Offline Mr. Scram

  • Super Contributor
  • ***
  • Posts: 9821
  • Country: 00
  • Display aficionado
Re: Another reason to hate "soft touch" power switches
« Reply #12 on: July 18, 2019, 04:24:42 pm »
Even if the graceful shutdown were an excuse not being able to turn off the screen or fan is inexcusable.
 

Offline ejeffrey

  • Super Contributor
  • ***
  • Posts: 4033
  • Country: us
Re: Another reason to hate "soft touch" power switches
« Reply #13 on: July 18, 2019, 04:50:11 pm »
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.
 

Offline IDEngineerTopic starter

  • Super Contributor
  • ***
  • Posts: 1950
  • Country: us
Re: Another reason to hate "soft touch" power switches
« Reply #14 on: July 18, 2019, 04:50:20 pm »
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.
I'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.
 

Offline IDEngineerTopic starter

  • Super Contributor
  • ***
  • Posts: 1950
  • Country: us
Re: Another reason to hate "soft touch" power switches
« Reply #15 on: July 18, 2019, 04:51:42 pm »
Anyway as we said: switched power strips. Done.
What 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 that every single time.
« Last Edit: July 18, 2019, 04:56:18 pm by IDEngineer »
 
The following users thanked this post: Mr. Scram

Offline IDEngineerTopic starter

  • Super Contributor
  • ***
  • Posts: 1950
  • Country: us
Re: Another reason to hate "soft touch" power switches
« Reply #16 on: July 18, 2019, 04:55:18 pm »
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.
Then 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.
 

Offline exe

  • Supporter
  • ****
  • Posts: 2647
  • Country: nl
  • self-educated hobbyist
Re: Another reason to hate "soft touch" power switches
« Reply #17 on: July 18, 2019, 04:55:59 pm »
Anyway as we said: switched power strips. Done.
What about the supposed "can't abruptly interrupt power or you'll corrupt internal data storage?" A power strip would risk that every single time.

Just keep it read-only.
 

Offline ejeffrey

  • Super Contributor
  • ***
  • Posts: 4033
  • Country: us
Re: Another reason to hate "soft touch" power switches
« Reply #18 on: July 18, 2019, 04:59:54 pm »
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.
 

Offline IDEngineerTopic starter

  • Super Contributor
  • ***
  • Posts: 1950
  • Country: us
Re: Another reason to hate "soft touch" power switches
« Reply #19 on: July 18, 2019, 05:00:24 pm »
Anyway as we said: switched power strips. Done.
What about the supposed "can't abruptly interrupt power or you'll corrupt internal data storage?" A power strip would risk that every single time.
Just keep it read-only.
Sometimes not an option for "embedded OS equipment". 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.
« Last Edit: July 18, 2019, 05:02:26 pm by IDEngineer »
 

Offline IDEngineerTopic starter

  • Super Contributor
  • ***
  • Posts: 1950
  • Country: us
Re: Another reason to hate "soft touch" power switches
« Reply #20 on: July 18, 2019, 05:02:10 pm »
...data corruption is mostly not a real problem since instruments have to handle power failures without bricking anyway.
And based on that point, soft touch power switching is unnecessary.
 

Online SiliconWizard

  • Super Contributor
  • ***
  • Posts: 15797
  • Country: fr
Re: Another reason to hate "soft touch" power switches
« Reply #21 on: July 18, 2019, 05:04:48 pm »
Anyway as we said: switched power strips. Done.
What 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 that every single time.

Uh. 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.

 

Offline IDEngineerTopic starter

  • Super Contributor
  • ***
  • Posts: 1950
  • Country: us
Re: Another reason to hate "soft touch" power switches
« Reply #22 on: July 18, 2019, 05:10:31 pm »
Uh. 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.
A 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.)
 

Offline Stray Electron

  • Super Contributor
  • ***
  • Posts: 2253
Re: Another reason to hate "soft touch" power switches
« Reply #23 on: July 18, 2019, 05:35:21 pm »
   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.
 

Offline IDEngineerTopic starter

  • Super Contributor
  • ***
  • Posts: 1950
  • Country: us
Re: Another reason to hate "soft touch" power switches
« Reply #24 on: July 18, 2019, 05:41:35 pm »
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.
There'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!
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf