It really depends on the task. If awake only long enough for computation, 8 or 16 MHz uses less power. If you're waiting for a communications reply or something like that, 1 MHz would use less power. So in your situation, I'm sure 1 MHz is the way to go.
Have you had any problems running at 1 MHz? I got some unstable results at 1 MHz. 2 and 4 MHz were fine, but at 1 MHz there were timing issues. It could have just been the sensors I was working with.
[quote author=Jack Christensen link=topic=235595.msg1735171#msg1735171 date=1400802666]I'm really happy with the way the data logger works and the power consumption looks like it probably exceeded my expectations by a fair amount. The logging cycle can be as short as 15ms depending on sensors. Just received data from a couple loggers that were in Northern Michigan through the winter. The first was inside an insulated but unheated cabin where temperatures got down to 1°F. Its regulator was configured for 3.3V. It started with a less-than-fresh pair of AA cells, that measured 3003mV at the start, and 2987mV after 184 days. The second logger was in an open shed. It used 5V, and its battery started at 3255mV and ended at 2844mV after 195 days with temperatures as low as -22°F. It had more sensors and more complex sensors than the first unit; I don't have current measurements but I imagine its sensors drew 2-4 times more current than those of the first unit, and for longer intervals.
I can tell you get a kick out of the low power capabilities these MCUs have. So do I![/quote]
Yes, I'm a little passionate about ULP MCUs. I love the battery stats you provide, I do the same thing. I have an ULP test unit I've setup as a torture device on my desk at work. I just tested the voltage again and at 230 days the average AA battery voltage is 1.41 volts (down from a 1.62 volt start). This is my torture device, which is setup to trigger much more frequent than normal.
What voltage regulators do you use? I've been using the Microchip MCP1700/MCP1702 which has a very low quiescent current (2 µA). What are you using for a boost regulator?
Tim