@neverdie Yeah, I think starting a dedicated thread is the right move.
That sounds a lot like what I'm trying to do. Prioritize load (boot/transmission) power, then dump into a reserve. This make sense when light is strong, but when solar isn't producing, how do you get power from the reserve to the load capacitors. Would you boost it?
@neverdie said in 
Effective Solar Supercap Boost Charger for Small Solar Panel:
@ncollins Here's the load switch that I've been using: http://www.ti.com/product/TPS22860 I like it a lot. I think it, or something similar, should be in everyone's tool box.
Awesome, I'll order a few. Appreciate the info, thanks.
@neverdie yeah, the fixed hysteresis of the internal BOD (328p, NRF51) isn't wide enough to handle startup for my nodes. I'm guessing it's due to the high ESR and corresponding voltage drop of the supercaps I've been favoring.
I also didn't realize how chatty mysensors can be during start up. My latest nodes have MY_PASSIVE_NODE enabled, skip presentation, and use dumb sleep.
@neverdie With all of your energy harvesting approaches, how are you handling unforeseen restarts? Almost all of my harvesting sensors have the same issue: if they drop below 1.8v (depending on BOD) they can't recover without manual intervention. Only one of my nodes has ever recovered and I think it's because the solar panel produced enough current to push through the MCU and radio startup.
My thought was to use the MIC2778 supervisor ic (datasheet), which has programable hysteresis, and a mosfet to wait for supercap/battery to reach a voltage high enough to handle a cold start.
@neverdie It's mostly because I haven't figured out how to appropriately, efficiently handle the wide voltage range of the 3722s.
In ambient light, they'd be perfect, but most locations in my house, there's a chance they'd get hit with direct sunlight. In a couple of my earlier prototypes, I fried the NRF module after the supercap exceeded 3.6v (damaged something that causes them to draw ~1-2ma).
In my case, I don't have a lot of artificial lighting, but I do decent direct/indirect sun from windows for at least part of the day.
Thoughts:
I'm mostly avoiding the issue by using the SC-3517s. A single cell wasn't really cutting it unless in direct sunlight, so I double up in parallel.
Bonus: other prototypes
Uses your boost charger
Testing out 50mF low ESR super cap
@neverdie at ~$1.90 per keychain, seems like a great way to get into harvesting.
I bet it would be easy enough to design and 3d print a replacement to the button half of the housing with a little more space for a radio and sensors.
I mean, you could probably just add an LDO, HT7333 or XC6206, and use it as is.
I've tried a lot of the aliexpress modules.
My experience with cheap modules
@waspie Given that all of my interrupt nodes stopped triggering after 36 hrs (before your reboot workaround), it has to be related. It’s just weird that my nodes would continue to wake up and broadcast battery level.
Is the LPCOMP interrupt method dependent on the wdt? Maybe resetting/restarting the wdt every 24hrs would suffice? Or maybe you have to reactivate LPCOMP every 36 hr wdt cycle?
@neverdie In theory, indoor is optimized for visible light spectrum. Outdoor, a combination of visible and IR. https://www.powerfilmsolar.com/about-us/the-horizon-blog/2018/08/10/outdoor-vs-indoor-solar-the-key-differences
But, who knows with these chinese panels. I haven't tested the indoor vs outdoor side by side. I do know these amorphous "outdoor" panels work significantly better indoors than the mono/polycrystalline panels I have.
