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David Brown
08/22/12 10:54
Read: 474 times
Klamath Falls Oregon

#188117 - more details
Responding to: Erik Malund's previous message
Thanks for the replies.

I could easily do away with the potentiometer and do something similar on the screen, but it will be mainly used by *ahem* older folks who won't be wearing their glasses and may not be computer savvy. We had figured that an actual knob would give the best tactile feedback, and be the easiest and most intuitive for them to use. But, I can just as easily put a massive 'knob' on one side of the (~10") screen.

Oliver: I hadn't thought about using a capacitive touchscreen with a molded plastic cover over the touchpanel. If the client is to believed, we could move 500 units next year, then 1000/year, then 2500/year, so the volume would allow for a pretty significant custom panel. It would also make assembly and sealing much easier.

I can easily change the input voltage to 12v. It would just make the boost regulator for the LED backlight work a little harder, and double the input current, but that's fine. Stefan, that article was pretty interesting. It seems that the limit is around 20v, below which electrocution is either very hard, or not possible.

An anecdotal story about that I recalled last night: A few years ago I got back home from a short trip to find a broken garden hose outside and 3 feet of water in my downstairs bedroom. I was less than amused. Of course the water level was over the level of the outlets, and the main breaker panel was in that room. As I waded through the water to turn off the power, I went to unplug my now floating alarm clock. As I got real close to the plug I felt a 'buzz' in the water with my hand. Then I grabbed the cord and yanked it out. Then I proceeded to flip all the breakers off. So basically, I had waded in water that was exposed to 110vAC in several places, and was fine, so 20vDC shouldn't be felt, even if the display cracks open and falls in the water.

Then the last possible hitch I forgot to mention, is that I also need an RS-485 connection to the rest of the system. But even that is just under 20Vp-p, so it may be fine. Eventually I may need an ethernet cable, but I I think I may just go with a wireless module instead.

Thanks again for the replies. I've already picked up a few good ideas :)

List of 22 messages in thread
Designing a product for use in water      David Brown      08/21/12 17:39      
   Have you considered silicone coating?      Richard Erlacher      08/21/12 21:11      
   one link      Stefan KAnev      08/21/12 22:04      
   Waterproof enclosures      Oliver Sedlacek      08/22/12 02:12      
      Projective touch - or maybe waterproof tablet      Per Westermark      08/22/12 06:27      
         If that potentiometer wasn't a hard requirement      Erik Malund      08/22/12 08:00      
            more details      David Brown      08/22/12 10:54      
               You might want to look into that a bit further      Richard Erlacher      08/22/12 13:33      
                  buttons for up/down gives tactile feedback      Per Westermark      08/22/12 14:12      
                     nevertheless, a strobe wheel rather than a pot ...      Richard Erlacher      08/22/12 15:24      
                        more good ideas      David Brown      08/22/12 16:42      
   Go to the lowest practical voltage      Jim Granville      08/22/12 16:20      
      answers      David Brown      08/22/12 17:39      
         Electric shock and intrinsically safe      Oliver Sedlacek      08/23/12 02:11      
            Isolators      David Brown      08/23/12 19:13      
               a question and a reference      Erik Malund      08/24/12 07:05      
                  answers      David Brown      08/24/12 10:55      
                     tethered unit??      Erik Malund      08/24/12 12:12      
                        mounted display      David Brown      08/24/12 12:32      
                           have you considered a combination of battery and solar?      Richard Erlacher      08/24/12 14:56      
                              indoor pool      David Brown      08/27/12 10:24      
                           Wireless chargers      Oliver Sedlacek      08/27/12 15:30      

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