Low-power remote power-independent (solar charged) sensor node!

Well, for a while now I've been entertaining the idea of building a remote sensor node to keep track/record of my indoors "balcony orchard".

This project here will be my starting point, a Low-Power Wireless Sensor Node where most of the work is already cut out for me.

It's power consumptions are reported to be:

Sleep Consumption 0.14 mA

Operating Consumption 13.57 mA

and the author says he can squeeze out around 6 months of operating power using a 540mAh 3V Coin Cell Battery. That would be more than enough for my requirements... but I put it into my head that I want to dabble with solar charging...

after some abbundant generic lmr searches and generic google fu I found quite a few interesting things on the subject, but I grow restless thus I decided that perhaps either:

Ni-Cd 60mAh 3.6V 14h 6mA Rechargable Battery Cells


Ni-MH 80mAh 3.6V 14h 8mA Rechargable Battery Cells

should be enough to keep the module running (assuming that the sensors I plan to add do not screw up my plans) continuously provided I don't run into a long series of overcast/dark days. Given that the module will take residence near a West faced window it will have plenty of solar exposition.

Regarding charging Ni-Cd and NiMH from all that read the easiest way to charge them is trickle charging at C/10, that is at 10% of their maximum capacity. (there are some issues however regarding longevidity of the NiMH batteries when doing this and other rates are recommended).

So I have my eye on this: 4.5V 5mA Solar Panel Power DC Battery Charger

to recharge batteries amounting to 3.6V from what I've seen it's recommended to use solar panels ranging from 4.5V-6V maximum output, and the reported current output is nearly 10% of at least the NiCd battery... and well I guess less can't hurt... it just charges even slower.

Regarding, circuit to do the inline solar charging I'm still looking for the simplest one I can get away with, this because of my self imposed design size constrains:

- design the module as small as possible

- least number of components

For now what only  occurs to be as the simplest is the use of a diode to prevent battery depletion during the night/dark hours. I guess that I should also make sure that recharging is only actived if the solar panel is delivering voltage over the minimum required threshold to actual recharge the battery.

So, that's all for now and I'll be accepting suggestions and the such if have some to give, or find any flaw in my reasoning :P