Im playing around with using a solar yard light to power a moteino. Solar cell charges a AA battery, then use a boost convertor to run the moteino.
The boost converters im looking at, with a AA at 0.8V (want to base it all on nearly dead battery), output around 50ma (raises to around 150ma at 1v).
My question is this, would it be beneficial to output 3.3v, and drive the moteino directly, or output 5v, then power via the moteinos VIN.
Dale, from the experimenting that my partner and I have done with boost converters, the higher the voltage required the more work the converter has to do == more current draw on the poor battery. The one we were using increased the voltage from 3.3 -> 7v for an anemometer. We found that by dropping down from 9v to 7v we gained more battery time.
One question would be if you have any other devices that need 5v along with the Moteino?
If you don't mind me asking which boost converters are you looking at for this project? I picked up one of those cheap yard lights last week and took it apart for something similar to what you're talking about here. I have the solar panel and rechargeable battery out but haven't had a chance to play with it yet.
Good luck on the project....would love to see more of what you're doing.
If you guys don't mind me throwing in my 2 cents...
Going through a boost to 5V then through a linear regulator down to 3.3V is more inefficient than just boosting to 3.3V. You basically loose efficiency twice, by working hard to boost that low voltage to 5V (the higher the boosting V the more you loose and the harder the booster works) and then by wasting some energy when you go down from 5V to 3.3V.
The downside of boost converters is they are noisy and can be expensive if you want a good low noise/ripple one. Linear regulators are much cheaper but they waste energy by converting it to heat in the regulating process. However if you only convert from 5V to 3.3V you don't waste so much energy. The inneficiency of linear regs is proportional to the difference between VIN/VOUT.
That said, the MCP1703 is a very low dropout regulator, and a very good compromise for the Moteino, hence why it was chosen. It gives most people a ready to go out of box solution without having to worry too much about how they will power the Moteino, as long as 3.5V+ is provided it will work reliably.
You can certainly hack the Moteino and bypass the regulator. You can provide your own 3.3V boosted to the 3.3V pin (desolder the regulator to avoid damage to it).