I'd use a DCDC Step up converter (there is a 1-5V to V mentioned in the MySensors shop). For a 5V device I'd not connect directly to the batteries, because the voltage might drop below 5V although the batteries are still far away from beeing empty. You don't want your approach with the diodes (or any other linear voltage regulator) because it wastes expensive energy to produce heat (In order to get the higher voltage down). With 3.3V Device I'd (and will in the near future :) ) try to just use two batteries (without regulator). They'll have 3V max. Voltage and Adrduino Pro mini / nrf24l01 work down to 1.9V - so most if not all of the charge from the battery can be used. (rechargeable batteries shouldn't go below 0.8V so this fits quiet nicely (2*0.85 = 1.9). Additionally I think it might be easier to use the 3.3 V Arduino over the 5V, because more lowpower people use it and because the power consumption typically drops if you use less voltage as long as we are talking about some mA. E.g. Modern CPUs are working <1V to keep down the (thermal) losses. As a last sentence: Designing real low power and battery applications is hard work. It is dependet on sofware but also -maybe somewhat more- on hardware. You must design/find a power supply that matches the application very well and have to think of the parts of your sensor/circuit you can / must switch off. Maybe some of them must be switched off in hardware (cut power supply). Then it is part of the software to re-enable them in the correct sequence and with proper startup times to have everything work. However for a start I'd recommend to try the mentioned ste up converter. But I fear it has a relative large quiescent current because it is able to deliver 500mA which is much. Maybe someone else knows some modules that suit better and have a defined quiescent current. Best regards DirkH

@gadu I'm sorry to bring up a post from the dead, but could someone point me in the right direction to find the MQTTGateway file/files for the RaspberryPI, i can only find the arduino ones and the possibility of a RPi one, here, but with no MakeFile to compile it.... Just a little background info and an ongoing topic located here at the forums of what I'm attempting to do and what is happening: Link

@Hacker007 I tried adding #include DigitalIO.h and sure enough it allowed the code to compile. I still am unsure if it will work due to incorrect radios from "Alice". Thanks for the comment.

@brad.s The transceivers communicate via RF via an embedded hardware protocol. The micro-controller communicates with the transceiver module using (standard) serial communication. Good radio communication and buffering of incoming or outgoing messages are more-or-less unaffected by clock speed of the micro-controller. So, it is not necessary to match clock speeds. The clock speed may affect energy consumption so you will want to optimize your arduino model for its sensor application and choice of using battery or mains power. Also, your choice of 5V or 3V3 IO will affect your sensor build strategy, having to power up or down to accommodate the IO requirements of the attached devices (e.g. radio transceiver 3.3V or a pressure sensor at 5V). Available SRAM/FLASH memory is also a factor, if you want to get into more complex devices later on.