Already spent over $700 on the project. I guess in for a penny - in for a pound. But I don't find a need for such info. I know when it rains. I can see what the water level is. The only electronics I need is a solar panel capable of keeping a 12V Lead Acid battery topped off (floating at 13.6V) so when the wife wants to run some water she just turns on a pump. A timer that she has to switch on again and again, which may be an inconvenience - but it beats the habit of her turning it on and forgetting to shut it off, burning up the motor and draining the battery flat dead. THAT is where I can see some electronics being involved. And there are plenty of circuits for building a timer that can run 15 minutes at a time.
Another night of rainfall and barrel set #2 is just above the inlet to the upper barrel. I definitely need to do better. I have a few plans in mind. Plug up two of the three weeping holes in both barrel sets and changing the connections to the downspouts. I'm losing some water there as well. Will put a reducer on top of the downspouts.
Rain should be ending tonight. Perhaps this barrel will become full too. Then after they're both filled up (Set #1 is full) I'll drain them. Go figure. But they'll be ready for full service next year.