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• Status: finished; partial success

  stoduk • 11/16/2015 at 13:35 • 0 comments

  This project was definitely a success, albeit not a total success. This biggest weak point was, as I expected, the user. There were other weak points though, so I'll document those here in case that helps others.

  These are roughly in date order

  Failures seen

  Intermittent power loss

  Some early problems were hit which were a bit odd, but the root cause was simply that the 8xAA cell holder had some really limp springs to hold the cells in place. Even gravity could cause the cells to lose their connection, and if any knock happened it would almost certainly cause an interruption.

  I never came up with a proper fix for this, but stretching the springs out periodically seemed to help. The real solution would just be a better cell holder, either with stiffer springs, or a better design. Sadly all the cell holders I could find (from ebay, Maplin, RS, etc.) all seemed to be the same poorly made item.

  Logging problems

  The script would logrotate at the beginning of running, then half way through it would copy the latest logs to USB drive, if present. This meant we could often end up with only a log for today (due to logrotate) and not a log for a full run (due to copying part way through the script). The easiest fix here would be to also copy off the rotated syslog files, but at no point did I hit a serious enough problem that I needed to fix that (which required updating the scripts, which was non-trivial).

  User failure
  

  The unit eventually died due to "fatal" problem. The fatal problem? Both sets of batteries died (the main power and the RTC backup battery), so things got a bit confused. Changing both sets of batteries would have fixed that.

  Doh!

  This is why making everything as idiot proof as possible is ideal, and remember that an idiot will always find a new way to be stupid that you didn't think of!

  System inaccessibility

  The top system box contained the RPi, the camera, the RTC, and extension leads running to the other box. This box was very firmly gaffer taped to a tree, to try to avoid any movement causing glitches in the time lapse output.

  To update the scripts required getting access to the RPi which I could do with a USB ethernet or WiFi dongle. Sometimes though accessing the RPi itself could have just made things quicker.

  To update the RTC backup cell would have definitely required opening the box, which would have risked disturbing the images. The lithium cell should have lasted long enough, but something cause premature death - maybe it was a cheap cell, or maybe the temperature fluctuations outside had a negative impact on life.

  Feedback to user
  

  The only feedback to the user when changing USB drive or batteries was the "accessing" LED on the USB drive. Good enough when everything worked, but not so good when things didn't work.

  To fix this would require better logging, or some sort of output indicating what problem had been hit - but to find something that was both low power and reliable was a challenge I didn't have time to fix. As with choosing the main power (where solar recharging would have been handy to reduce the number of site visits), I chose simplicity over everything else and that is a compromise.

  Sunlight

  We had problems early on with sunlight causing flare in images. Our attempts to make a makeshift lens hood caused more problems than they solved though, so in the end we intended to discard the few images a day that had the problem.

  Future improvement

  • Logging improvements, to at least beef up what feedback we had
  • Find a way to fix the camera securely but still providing access when needed. Alternatively: move everything to the second box or accessible from the second box.
  • Create a decent lens hood. 3D printing might be needed unless we can find something that already exists that exactly matches the field of view the camera requires.
  • solar charging of the main batteries would have been a massive improvement in one respect - as then if the user couldn't get on site things should keep running if all else was well (it obviously would mean...

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