I'm working on wireless sensor network project consisting of sensors based on ATmega328 and MRF24J40MA. The sensor is expected to stay asleep most of the time, waking up on regular intervals to collect sensor data and sporadically sending collected data over 802.15.4.
I'm not sure on how to power the circuitry for longer life on batteries. I consider two options:
Use LVD1117V33 to scale down 4xAA batteries to 3.3V. I guess this means batteries operational voltage range of 6V..3.3V.
Use NCP1402 to scale up 2xAA or 1xAA to 3.3V. I expect the battery to be drained nearly to its minimum until the circuity fails.
The second option sounds more promising, but don't I overlook something? Are there any options?
Best Answer
Your ATmega328 works down to 1.8V, the MRF down to 2.4V. A very simple solution would be to use two alkaline (or one LiSoCl2!) batteries without any conversion. The MRF will work down to 1.2V per battery. I don't know how much juice is left at that level, I could not find a graph in a few minutes googling.
Another simple option would be to use 3 alkaline batteries, and feed the MRF via a linear 2.7V regulator that is switched on only when needed (either a P-fet with a 3-leg regulator, or a regulator that has an off pin). If you parallel a few ATmega328 output pins you can probably even feed a 3-leg regulator directly. An MCP1702-2.7 has 0.7V dropout (?), so the batteries would be useful down to ( 2.7 + 0.7 ) / 3 = 1.13 V. If you want to be really clever: at 1.13V per battery you could let the ATmega328 feed the battery directly to the MRF, bypassing the regulator.