That's nice, good to know that something like this is experimented. Anyway, as I said the power supply wire is the issue now.
@Paul_B: Long story short, I was asked to help in a project modification, so it is a carry over. Unfortunately there is no time to reconsider the whole project (e.g remake it to low power consumption). Smaller AVR uC is not an option (flash and ram wise), different Arduino compatible (like Teensy) boards would be good.
@TomGeorge: basically a Mega board is installed with GSM, RTC and SD card module, plus a serial communication is established with an external sensor module. Sensor data is gathered, stored and sent.
Mains electricity is available, the problem is that it's a 20-25m away from the installation place. The idea is to wire only the 12V to the Mega board (lower risk regarding touch protection). The required cross sectional area is OK, I calculated it based on the current consumption.
What could be a pitfall with the long 12V power supply cable?
