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   XPost: sci.electronics.design   
      
   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.   
      
      
   > https://www.dropbox.com/scl/fi/bbhdy053xsdzv77g0brc5/B-box_Res   
   t_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.   
   >   
   > 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   
      
      
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