First of all, thanks for all the great info, advice, tips etc. available in this community. During the past few months it has been a fantastic resource for me.
Now, my question: I'd like to have an Arduino running from a battery, as long as possible. The Arduino is going to capture data (temperature, etc) and post it to the internet (via Ethernet shield or Wifi module). The data should only be captured like every 5 to 10 minutes. So to optimize battery life, the Arduino should/could sleep between two measurements.
I think that I'll need some sort of an external clock (RTC) in which an "alarm" can be created that will wake up the Arduino using an interrupt. Can anyone confirm this scenario can be accomplished? If so, what would be the expected "life time" of a number of rechargeable batteries (like 4 to 6 AA or AAA)? And finally, which RTC would be suitable for this?
"The clock operates in either the 24-hour or 12-hour format with active-low AM/PM indicator. Two programmable time-of-day alarms and a programmable square-wave output are provided."
Wake up, do the measurements, reset the alarm time, go back to sleep.
This is a bit of a problem with the Ethernet shield since it draws 200+mA! I may be wrong but It will be powered for the whole time that the arduino is.
I have tried to work around a similar problem, but I tried to power the Ethernet shield from a digital pin via a relay. This works nicely, but I can't get the Ethernet to set up properly after the Arduino has booted This could be a solution for also, when you wake up the arduino you could have it switch on the Ethernet shield too.
PaulS:
If you can run an ethernet cable to the Arduino, why can't you run power? An Arduino with ethernet shield on batteries does not make sense.
I second this, and would add that PoE makes a lot of sense for this purpose. You don't even have to implement 802.3af, you can just split off one of the unused pairs in your ethernet cable at both ends and use that pair to carry DC power. I'm currently doing just that for one project and I can testify that it works wonderfully.
It wakes up the mcu every second. In the timer1 isr, keep time, and test to see if enough time has passed. If not, go back to sleep. Otherwise, do something.
PaulS:
If you can run an ethernet cable to the Arduino, why can't you run power? An Arduino with ethernet shield on batteries does not make sense.
I second this, and would add that PoE makes a lot of sense for this purpose. You don't even have to implement 802.3af, you can just split off one of the unused pairs in your ethernet cable at both ends and use that pair to carry DC power. I'm currently doing just that for one project and I can testify that it works wonderfully.
Actually you guys are completely right about the Ethernet shield: if there is a cable there is power (or PoE). Still the scenario with the WiFi module (I have the Roving Networks RN XV that I can put on/off with a transistor) makes sense. Or I'm thinking about working with a 2.4Ghz wireless module ...
This could be a solution for also, when you wake up the arduino you could have it switch on the Ethernet shield too.