Quick update on where I stopped last time, I fixed the problem which was that too much current was flowing through the soil and destroying the probes through electrolysis. I fixed this by replacing one of the leads with another 68k resistor. I also couldn’t resist recreating the whole circuit again in an attempt to do a cleaner job. I didn’t succeed in that but at least the device works.
Having also gotten a hold of a 3V lithium cell I hot glued it to the back of the device and it works very well on it. So all in all since I started this project the voltage dropped from 9V experimentation to 5V first time deployed and now 3V, all with the same components. I should have taken that into account and put a lower value resistor for the LED as it’s a bit dim now but plenty to see it in darkness. It’s also nice knowing how little current it will be consuming.
The chilli seeds also started to sprout which is exciting.
I ordered a bunch of stuff from eBay that will hopefully start arriving soon so I can do more than just plants.