how feasible is it to run a 3.3v Arduino Pro mini and 16x2 3.3v LCD off of a 3.7v Li-poly battery? Will the slightly higher voltage damage any parts, or can they tolerate the small over voltage? Also, the miniature solar cells produce 350mV at the highest, and around 250mV in a well lit room. If I put 15 or so in parallel, and produce somewhere around 3.75v to 5v, can I cobble together a charger out of this?
Ultimately, I just need the screen to display something from memory every time a button is pressed, but if I can make it completely enclosed and never have to open it for interface or battery charging, that would be ideal.
Thanks so much for any answers to my (most probably) stupid questions!
A Lipo has a fully charged voltage of 4.2V. They are considered empty when reading 3V under load, ~3.7 off load.
So to charge, you need to provide at least 4.2V + the dropout of the charger regulator\IC. Take care with the charging as overcharging a Lipo leads to bad things happening.
Also take care not to discharge too much. Over discharging severely reduces cell life, if not destroying it completely.
Edit: I know I am grossly oversimplifying the circuit design, but I just want to get the basics straight in my head before I worry too much about the specifics…
You’ll need a different voltage regulator. The ones you’ve listed have a dropout of 2V, this means that the regulator itself drops 2v from it’s input to its output. This won’t play well with trying to drive 3.3V from a LiPo.
You need to use an LDO (Low Drop Out) regulator when using a single LiPo cell on a 3,3v system.
The Arduino Pro has an on-board regulator (a MIC5205) which is an LDO type, this is good for 150mA with a dropout voltage of 165mV at full rated output. I don’t know if the 150mA output of this would be sufficient for the Arduino and the LCD.