Hi Bob, thanks for the tips.

I’m thinking that the Timer Hat will make a big difference. The Hat is quoted at 35nA or 115nW, which is nothing! I was looking at 10 minute intervals, but it has 5 or 20 minutes intervals, so I might put it back to sleep on every second wake-up. If the Pico runs for 1.1 minutes, 6 times per hour, that’s ~160 min / day @ 22mW, approx 60mWh per day. Transmission is 0.25W but for < 1 sec at a time (?), 144 times per day?

You are right in that I need to account for inefficiencies and I don’t know how much the sensor draws in it’s 1 minute warm up, or if the 915MHz transceiver draws while ‘idle’ for most of that 1.1 minutes. So I’ve been rounding up numbers.

From what I know, I’m calculating about 570mWh per day. If the extras (eg, warm up) adds 50%, rounding up goes to 855mW per day … 260mAh. The panel will power the system for a reasonable number of daylight hours, and should have plenty of time to top up the LiPo, so I’m now thinking of the 400mAh LiPo.

I’m looking at a LM2940 voltage regulator, which should only have a 0.5V drop, connected to Vsys on the Hat. How much power will I loose between this and the Hat itself? No idea. But if I can get the Timer Hat to work as specified, I’ll hopefully only need about 2 hours per day @ 0.5W from the panel, to re-charge.

The other unknown is that after 2 x 5 minute intervals, plus 1.1 minutes ‘awake’, it will effectively be transmitting at 11.1 minute intervals, not a nice number. I don’t know if the interval starts from the start or the end of the last ‘awake’ period. If I have to run longer, to get ‘nice’ interval, that will have a significant affect on power (and I might need the bigger battery).

Happy to receive any other tips you may have. Cheers, Dave