However, other devices may not tolerate the low voltage or erratic current delivery of dying batteries. What other hardware will you be using?
Running ATMEGA328P-PU, which is pico power, right?
Speed Grade:- 0 - 4 MHz@1.8 - 5.5V, 0 - 10 MHz@2.7 - 5.5.V, 0 - 20 MHz @ 4.5 - 5.5V
For one, an nRF24L01 radio. It's rated for 1.9-3.6. So I guess if I went with straight batteries, I could stack 3 as far as that guy is concerned.
For temp, I had been looking at MCP9700 which can go down only 2.3V.
1.2 * 3 = 3.6. That gets you nicely into the 10 MHz band allowing you to reliably run the processor at 8 MHz.
If you can, running the processor at 1 MHz will significantly increase the battery life.
Yeah, all is well on the day with fresh new batteries
I suppose the thing to do here is just run a dying batteries test.
Oooh, scary! :O I'm just wrapping my head around 8 MHz. Is there even a boards configuration for lower?
The input can be anything from 1.0 to 5.5V, so this can also be used with 2x or 3x AA battery packs (even 4, if NiMh), and it will continue to work when hooked up to a 5V power supply. The regulator will work down to less than 0.5V and can squeeze the very last bit of energy from the battery.
ST makes a booster - L6920 - that is about the best I've found in terms of quiescent power consumption (down to some 20uA or less depending on input voltage) and low voltage startup behavior. This will run down to 0.5V or so (actually, 0.4xx V in practice if you're not drawing much current). Not sure how low in cost you want to go; there are definitely cheaper ones out there if you don't mind higher idle current.
Do you have any plans or schematics online? I'm also working on a very low-powered Arduino variant geared toward energy harvesting projects; might be good to compare notes.
I want to build a drift buoy to send off to see if it could make it across the pacific, using ocean currents at particular depths as a conveyor and pressure sensor to determine depth. I will have a 'report' routine where it will surface and get a GPS location, charge the batteries with a solar cell, and transmit its data points and location to me using ULF. Obviously I want the thing to be using little-no power when it isn't collecting data or transmitting...