This project is not dead; 5 years is just a long time.

So, what's been going on? Well, in a few weeks I will be burying the 4th unit in a 4th time capsule (the time capsules are staggered - every year there is one to dig up from 5 years ago.) So it will still be 2 long years before I get the original unit back from 2018 to see if it worked.

However, this means that I have just used up the last unit I have in stock, and I'll need to build another batch of them. This probably calls for a PCB redesign; there are definitely some improvements I can see to be made. It certainly helps that for the past 3 years, I've taken a job in which I regularly make PCB designs, so my skills in that have improved significantly, as well as my skills in working with and soldering SMD components. If only we weren't living in the silicon shortage timeline - genuine BME280 sensors have been out of stock for months, as have even the humble AtMega328P.

This year, I decided to try something a bit more robust by spot welding the batteries together instead of putting them in one of those crappy battery holders. I built the spot welder for doing 18650 batteries, but I figured it could serve me well here too. Only risk it that I blow through the case of the battery with too much current, and make a hole which drains out all the electrolyte. Seems to be OK so far, but only time will tell, unfortunately.

As for the units I have decided to keep around for observation: one was in a plastic food container placed outside my house. All was going well until spring of 2021, when I found the container had cracked and filled with water. In fact, the board had been entirely underwater for some weeks. After cleaning up the corrosion, I managed to extract the data that was on it, and left it to dry indoors. When I finally got back to the seemingly trashed unit after several days, I changed out the batteries and to my surprise, it worked again, and has been running most of the year (indoors). I have not checked in quite a while to see if the BME280 sensor was at all damaged by the flooding. I would actually be surprised if it does work correctly, but I don't consider this unit as part of the fleet anymore anyhow.

The other unit I have access to (sometimes) is at my summer vacation spot. It's protected from the elements somewhat, but still sees freezing temperatures for much of the winter. I placed this unit in the summer of 2019 and checked in on it in the summer of 2020 and 2021. Both check-ins seemed to prove the unit was working just fine; battery voltage was good, the data read off cleanly, and the time was only off by less than a minute both years.

However, for longevity, the oldest unit is still the 2018 one buried inside a PVC pipe underground, and I won't see it again for another couple years.

I also rewrote the firmware, as I've gotten better at doing stuff like that too (at least I hope so). The units are now controlled mostly through a serial port command console interface, so the DIP switches aren't really needed anymore.  The new software, along with some example scripts for Python and Octave for graphing the dumped data, are on Github here (https://github.com/alnwlsn/envilog2), which I've started to try out despite not really being a software guy.

That's all for now though, see you in 2 years.