@neverdie Yep, I had the same experience with this LTC3108 breakout.
https://www.aliexpress.com/item/LTC3108-1-Ultra-Low-Voltage-Boost-Converter-Power-Manager-Breakout-Development-Board-Module-Diy-Kit/32867270266.html

I also intended to try the following modules which have a ton of functionality baked in. Unfortunately, they multiply the cost of a basic node by 2-5x.

BQ25570
https://www.aliexpress.com/item/32903287631.html

BQ25504
https://www.aliexpress.com/item/32976994195.html

From an energy harvesting perspective, I think rechargeable watch battery + 0.2F super cap + 4 100uf is my favorite setup. Cheap, fault tolerant, very small profile if you use 1206 ceramic capacitors (not shown in this prototype). Based on this design: https://www.allaboutcircuits.com/technical-articles/overview-of-the-ble-solar-beacon-from-cypress-semiconductor/

0.2F 3.3v Capacitors
https://www.aliexpress.com/item/32577753501.html

3v Rechargeable Battery
https://www.aliexpress.com/item/32813917590.html

1206 100uf Capacitors
https://www.aliexpress.com/item/32376068793.html

Cheapest amorphous, indoor solar panels I have found: 2.7-3v
https://www.aliexpress.com/item/1854641441.html

Tiny S4 1N5817 Diodes
https://www.aliexpress.com/item/32813213875.html

LTC3108 -1 Ultra Low Voltage Boost Converter Power Manager Breakout Development Board Module Diy Kit

$6.43

Energy Harvesting Module Boost Converter Solar Cell Management Energy Collector CJMCU-25504 bq25504

$9.30

HOT NEW battery MS412FE MS412FE-FL26E 3V Rechargeable Button battery charging with leg 20pcs/lot

$25.76

1206 SMD capacitor 100uf 16V 107Z 100pcs X7R

$4.05

Free Shipping! 10pcs TRONY low-light-type amorphous silicon solar panel photo module sensor

$5.74

New 1N5817 SOD-523 silk screen S4 Schottky diode 1A 20V 5817 SOD523

$1.00

@neverdie according to a few datasheets 2v at 200lux. The solar cells delivered were HENGYANG SC-3514.

http://www.vimun.cn/en/ProductInfo.asp?pid=18
http://www.solars-china.com/solars/indoor-solar-cells.pdf

On my windowsill, 2.5v typical in-direct sunlight, 2.7v is the highest I've recorded in direct sunlight.

So far, most of my Aliexpress buys have been fine for my needs. Haven't really gotten close to making a "production ready" module, so for prototyping it's been fine.

One exception: I thought I had a genius idea to repurpose these $1 solar powered keychain flashlights. They had an amorphous solar panel, rechargeable battery, button, leds and a housing...for $1. I bought 20 of them. First one I opened up, I realized it's a lie!

The solar panel is just glued to the circuit. The battery is just a normal non-rechargeable CR2016.

@sebex

I've tried a lot of the aliexpress modules.

My experience with cheap modules

• Cheap, generic SMD NRF24L01+ have always outperformed the non-smd cheap versions
  • https://www.aliexpress.com/item/32840721455.html
• Avoid the cheap PA/LNA modules at all cost
• eByte, cdsenet, cojxu (all ebyte companies) have the best of the chinese modules. They are on sale often. I exclusively use their PA/LNA modules for gateways and repeaters.
  • https://www.aliexpress.com/store/2798183
  • https://cdebyte.aliexpress.com/store/2077046
  • https://www.aliexpress.com/store/4836041

5PCS WAVGAT Component Kit NRF24l01+ 2.4GHz Wireless Module Mini Version Power enhanced version SMD

$4.19

@waspie appreciate it, thank you

@neverdie they work super well. I've been testing them for a few months now, very reliable.

One of the first supercap setups I made, "SolarRed". It's been running non-stop for 8ish months sitting indoors on a windowsill.

6 Month History SolarRed

Testing platform for different solar panel / super cap combos

With all the NRF52 modules from EBYTE I've tried, the only way I can flash them is over SWDIO, SWCLK, GND, VCC via JLink clone.

And, before flashing is possible, I have to unlock the module by following these directions: https://github.com/micooke/arduino-nRF5-smartwatches/blob/master/nrf52_disable_read_protection.txt

@neverdie I was surprised to find the deceptive $1 solar keychain actually used a decent indoor solar cell. I can't find similar spec'd solar cell for less than $3 (at 10-20pcs). Despite the blatant false advertising, they're actually worth salvaging, especially with a solderable CR2032.

@steven987 I would argue the perfect battery setup is a single AA or AAA LiFePO4.

• No boost or regulator needed, nominal voltage: 3.2v
• Much safer than traditional LiPo/Li-ion
• Really easy to solar charge with TP5000 module and cheap solar cells

Cons

• they're not super available
• a little pricier
• require a LiFePO4 charger
• still potential for fire with enough abuse
• Significantly less power density than NiMH or alkaline

LiFeP04 Batteries
https://www.ebay.com/itm/12X-SOSHINE-LIFEPO4-AAA-10440-BATTERY-280MAH-3-2V-FOR-WIRELESS-MOUSE-ALARM-TOY/333294469931?hash=item4d99e6032b:g:lk0AAOSw04ddULoH

TP5000 Charging Module (I use for solar charger)
https://www.aliexpress.com/item/32807030878.html

Solar Cells
https://www.aliexpress.com/item/32882323830.html?spm=2114.12010612.8148356.16.192a59c23u0hej

SUNYIMA 10pcs Poly Solar Panels 5.5V 80MA Polycrystalline Solar Plate Cells DIY Solar Battery Charger Sunpower System 60*60MM

$9.76

+1

I've tried the E73 Ebyte NRF52832 modules, various NRF51822, and "diymroe" STM32F407, all with the same result...not seeing anything and nothing to serial out.

Somebody with more experience with hardware debugging could probably dive deeper using STLINK / JLINK tools.

I know there are a few issues related to their use on github:

https://github.com/mysensors/NodeManager/issues/463
https://github.com/mysensors/NodeManager/pull/438

I also remember the project owner, @user2684, mentioned he doesn't get notifications from the MySensors forum, best to open an issue via github.

mitchmitchell created this issue in mysensors/NodeManager

closed On STM32 HyTiny board, NodeManager gets SIGSEGV signal #463

user2684 created this issue in mysensors/NodeManager

closed Pre-release bug fixes #438

@waspie just to follow up, 24hr reboot() is working perfectly. Appreciate the help.

With all the NRF52 modules from EBYTE I've tried, the only way I can flash them is over SWDIO, SWCLK, GND, VCC via JLink clone.

And, before flashing is possible, I have to unlock the module by following these directions: https://github.com/micooke/arduino-nRF5-smartwatches/blob/master/nrf52_disable_read_protection.txt

@Joost For the price, this could be a simple way to start
https://www.electrodragon.com/product/atmega328p-arduino-plus-lora-sx1278-board-loraduino/, though it's not exactly what you're asking for.

@p359 Which version of Arduino IDE are you using? I was seeing that with 1.8.10, but I ended up downgrading to 1.8.6 to test and it worked.

@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:

• add a really efficient LDO between the 3722 and the super cap
• Sacrifice size compact size and jump up to 5.5v supercaps. Add LDO between the supercap and mote
• rig some kind of a pass through when vout < 3.6, else go through LDO

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.

@sebex

I've tried a lot of the aliexpress modules.

My experience with cheap modules

• Cheap, generic SMD NRF24L01+ have always outperformed the non-smd cheap versions
  • https://www.aliexpress.com/item/32840721455.html
• Avoid the cheap PA/LNA modules at all cost
• eByte, cdsenet, cojxu (all ebyte companies) have the best of the chinese modules. They are on sale often. I exclusively use their PA/LNA modules for gateways and repeaters.
  • https://www.aliexpress.com/store/2798183
  • https://cdebyte.aliexpress.com/store/2077046
  • https://www.aliexpress.com/store/4836041

5PCS WAVGAT Component Kit NRF24l01+ 2.4GHz Wireless Module Mini Version Power enhanced version SMD

$4.19