I'm getting started putting together a Moteino based sensor to measure the snow depth in my back yard. My idea is to put together a Moteino and a PowerShield interfaced to a LaserRangeFinder:
https://www.amazon.com/gp/product/B07L8B2FVK/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1. The LRF would be on an arm sticking out from a tripod support that has solar cells, and a weather-proof box containing the electronics. I'm hoping to power the system with SuperCap and solar. Since the sensor is to be out in the snow, I plan to put the solar cell(s) vertically to prevent snow build-up on the solar cell(s). At the moment the mounting is conceptual; I'll try to make some drawings that I can post another day.
Question 1: I'm not particularly constrained size-wise, so I can use up to 3 110x92mm 6V solar cells to charge my SuperCap. Each solar cell would charge the cap through a Schottky diode, and the 5.4V Super cap protected from overcharging with a 5.1V zener diode. The solar cell(s) are 200ma; so worst case, the zener diode would be dissipating .9V @ 200ma(x3) = .54W. Do I actually need a fancy charge controller as discussed in some other threads?
My thoughts are that using a MPPT charge controller is counter productive. When the cap is discharged, you want maximum current at low voltage; when the cap is nearly charged, you want maximum voltage at whatever current you can get. A max power point controller adjusts the voltage out to maximize the power, so probably not the highest voltage. Anyway it seems like needless complexity unless the leakage through the zener diode is too high when not charging.
Question 2: My sensor is peak current of 140ma, "average" current of 110ma at 5(+-0.5)V. Their use case is some form of continuous measurement, but I would only sample at most every minute. They don't specify the idle current. I would like to switch on the power to the sensor shortly before taking a measurement, then turn it off again. Will something like the circuit in the attached image work? (Image from
https://lowpowerlab.com/forum/moteino/using-moteino-r6-in-extremely-low-power-project/msg26879/#msg26879) I would use the prototyping area on the PowerShield to build the PFET circuit (I have NDP6020P).
A possible alternative to the PFET circuit would be to use a TPL5110 BoB from LPL to control the power to the LRF; seems overkill. I think I would need two digital outs from the Moteino, one to turn on the LRF through the Delay input, and one to turn off the LRF through the Done input. Would the TPL5110 smoke if I feed it 5V from the PowerShield?
I haven't thought much about what to do if the capacitor discharges below the BOD of the Moteino. I'm going to try to have enough solar power that I never reach that point.
I'll post pictures as I progress.