Great points – I’m still thinking about the best way to do this. The information I need is the amount of watering done over the previous week (or whatever specified time interval – as you state you have some 2 week cycles.)
Here is what I consider to be the worst case scenario. I see in another post that somebody has 6 expansion boards. That’s 56 zones. If every zone was activated 3x per day every day, you’d end up with over 1000 entries per week. I did say ‘worst case’ ;). In my real-world case, I have 24 zones that are activated 3x per day 3x per week. That’s only 200 entries. I’m worried about consume too much memory, but maybe I’m over-thinking it. Currently my Pi (128MB version) has 23MB of free RAM, so there does appear to be plenty of memory even for 1000 entries.