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   PID: SoupGate-Win32 v1.05   
   XPost: sci.electronics.design   
      
   On Tue, 17 Sep 2024 11:07:17 +0100, The Natural Philosopher   
    wrote:   
      
   >On 17/09/2024 03:58, john larkin wrote:   
   >> The RP2040 has a cool mode where it can be made to boot up with the   
   >> USB port looking like a memory stick. That's great for software   
   >> installs or upgrades. The Pico board has a BOOT button on the board;   
   >> if the pico is powered up with the button pushed, it goes into that   
   >> boot mode.   
   >>   
   >> But if I have a product (actually a family of products) in a nice   
   >> aluminum box, a user would have to remove the top cover, remove all   
   >> power sources (there can be three), and hold the button down while   
   >> reconnecting power.   
   >>   
   >> Some of my customers also want to lock a box such that it's impossible   
   >> to write to any nonvolatile memory while it's in a secure area.   
   >>   
   >> So here's an idea: a small hole in the box allows a toothpick or a   
   >> paper clip to push a button. A short push is a regular reset. A long   
   >> push is a memory-stick mode boot. We can have a rotary switch LOCK   
   >> hole too.   
   >>   
   >Thats' what my PICO powered thermostats have. For the onboard button though   
   >Resetting is done by pulling the power.   
   >   
   >The point is that if you do power up with the button pressed, you wipe   
   >the entire FLASH RAM I think.   
      
   If BOOT- is low at the end of reset, it powers up in USB memory stick   
   mode. I don't think that wipes the files stored in the big serial   
   flash.   
      
      
   >   
   >   
   >> https://www.dropbox.com/scl/fi/bbhdy053xsdzv77g0brc5/B-box_Re   
   et_Button_3.jpg?rlkey=40ozzdvczf4z8625u8i081a9b&raw=1   
   >>   
   >> Does that look like it will work? The paranoid customer can pave over   
   >> the two holes, and even the end-plate screws, with an official-looking   
   >> sticker.   
   >At a brief glance, yes, but I donbt see why a simmle disconnect power   
   >switch in addition to the onboard switch wouldn't be as easy.   
      
   There are three potential power sources to disconnect, and I don't   
   really want a power switch.   
      
   >>   
   >> Schmitt trigger U3 is unfortunate and likely unnecessary, but it   
   >> insures against a low-probability hazard.   
   >>   
   >Once you start laying out a board, put everything on it you may need,   
   >Can always leave it out later   
      
   The schmitt adds way under a tenth of a per cent to the board area and   
   the cost, so may as well leave it in.   
      
   --- SoupGate-Win32 v1.05   
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