| Electronics > Projects, Designs, and Technical Stuff |
| Another reason to hate "soft touch" power switches |
| << < (9/13) > >> |
| tooki:
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.) |
| IDEngineer:
--- Quote from: tooki 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. --- End quote --- 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. |
| tautech:
--- Quote from: IDEngineer on July 18, 2019, 11:46:49 pm --- --- Quote from: tooki 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. --- End quote --- 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. --- End quote --- 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. |
| IDEngineer:
--- Quote from: tautech on July 19, 2019, 12:40:41 am ---And there ^ you have it, hard switch Windoze OS'es and see how you get on. --- End quote --- 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 --- End quote --- But it doesn't have to be. It's just lazy engineering. |
| rsjsouza:
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). |
| Navigation |
| Message Index |
| Next page |
| Previous page |