Hi All,
I would like to use an 18650 Lithium battery to power my project. These standard batteries have a nominal rating of 3.7v (I think) but will provide 4.2v when fully charged, and I'm not sure how low it gets, though probably around 3.5 is a good stopping point.
So this seems to be alright for ATtiny chips, which appear to be happy from 1.8v to 5.5v. I'm guessing I could just use the battery directly for those.
But I was thinking of using a 3.3v MSP430 chip (from a "value line" G2 Launchpad) to conserve power (it seems they can sleep really well). It doesn't like anything above 3.6v. Easy-peasy, I can add a 3.3v voltage regulator.
But the project I'm thinking of has a servo, which from what I can tell needs over 4 volts to work (or am I wrong on that)?
Anyway, here is the project: Charlie and the Treat Dispenser
Right now I'm using one of those USB cell phone chargers that contains an 18650 battery and it produces 5 volt to run the Arduino Pro Mini and the servo.
However, it only lasts a day - and the servo stops responding if we stay up really late 
So I was hoping to make the whole thing more power efficient. Partly just to see how and if it can be done, as really I suppose I could plug that sucker in 
My thoughts about the existing project power usage are that:
1) I'm losing a lot of power just having that charger up-converting to 5v
2) The Arduino pro mini is on all the time, using up power that way.
3) The servo rarely gets used - the unit is usually on standby.
If I could set this up to run on the MSP430 launchpad, I can make it sleep most of the time, and wake when the button is pressed. The only time it needs to be awake is to handle that button press to dispense the treats, so that setup should work charmingly well (in theory at least).
So the question is - what is a decently efficient way of doing this? (I don't need "most" efficient)
It needs to power the chip (Arduino Pro Mini or trinket, ATtiny, MSP430 are what I have here) and the servo.
I'm thinking that the voltage regulator will suck up some power (but how much, and is there an efficient way to hook that up?), and up converting to 5v will suck up power.
Maybe the up converting circuit to run the servo could be placed on the other end of a transistor that gets switched on when needed?
edit, ps: I currently turn off the servo by using "servo.detach()". It still does have power supplied to it at all times, but it doesn't do the buzzing thing that the servo was doing if I kept it attached. I could try using a pin to switch a transistor to the servo power line to see if that helps at all.
Thanks!
-Nico
