Well, Design of an home made electronic kit for my 10yo daughter to teach her by example. on 74HC595 (shift reg), 9 leds, 4 push buttons, some wrapping wire, ... We managed to build it, it works, with some bad contacts, but it works, she enjoyed the thing and the time spent together. Here is the schema and the pictures. I strongly invite parents to build it with their children, easy and fun. !
My 3V Node (Atmega328P 1MHz), embedded NRF24L01+ with ceramic antenna, ATSHA256, AT25DF512, BME208, LED, Battery monitoring, ICSP, FTDI, Castelizable, Breadboardable. 
Well,in my case, I mounted and tried to fix bugs in my very first design. This is supposed to be a castelizable Sensebender compatible node, embedding NRF24L01+, LED, Temp/Humi/Press sensor, Memory, crypto, with most of the IO exposed. The updated design is online, but still work in progress. 
project on OpenHardware
Hi @sundberg84 , Just in case, I redesigned the whole thing to fix some issues. This is still a work in progress, but it is very close to the final design.
@skywatch The issue I can see with steppers is that your camera might move when you poweroff the motors. As you said, when you poweroff them, they wont go back to center, but they also wont keep the position. If your camera is not perfectly balanced, it will "fall down". As well as your 3D printer : as long as you power the steppers, you can not move the axis, but as soon as you poweroff them (unlock) , you can move your axis.
@rvendrame sorry, I did not see your comment. Yes, it is VERY valuable. Thanks a lot
@rvendrame Thanks a lot, I'm currently working on another project (electronic load). But I keep your idea in mind and will investigate when I'll continue this sensors project.
@monte A little bit less, but not a lot. I still need to improve the PCB (better castelization tracks, remove diodes, ...) and this should be ready to be copied/used.
@pihome I did compile my own dualoptiboot for 1Mhz support. My board does not use any LDO (I am supposed to only plug 3V power supply, not more). The LED is not a "power LED" but a LED connected to A2 to be used (or not) by the sketch. I might have more current consumption because I use PA_MAX as transmission power. or because my sketch does not put BME280 in sleep mode (yet). I still need to rework on the schema and PCB to tune/optimize it (no need for the zener, the schottky and the FTDI connector), but the proof of concept for my very first real design works.
My 3V Node (Atmega328P 1MHz), embedded NRF24L01+ with ceramic antenna, ATSHA256, AT25DF512, BME208, LED, Battery monitoring, ICSP, FTDI, Castelizable, Breadboardable.
@pihome A simple wakeup cycle lasts 1.2s at 20mA. In theory, I should have 10 hours of wakeup time.
@pihome I finally built it. There will still be some adjustments (routing for cutting castelized holes, diode protections removal, ...), but it works. Be careful, it is designed to have 2V-3.6V for power AND signals (double check your ICSP and FTDI programmers). The battery duration depends on your sketch (sleep time, transmission power, encryption ...), your battery (mAh), your sensors (I only have BME280 connected) and your gateway distance. I can tell you that it uses 13mA during transmissions at PA_MAX.
Well, Design of an home made electronic kit for my 10yo daughter to teach her by example. on 74HC595 (shift reg), 9 leds, 4 push buttons, some wrapping wire, ... We managed to build it, it works, with some bad contacts, but it works, she enjoyed the thing and the time spent together. Here is the schema and the pictures. I strongly invite parents to build it with their children, easy and fun. !
@pihome I don't know yet, I'm still waiting for the PCB. I should receive them this week. From the mysensors site, 1Mhz vs 8Mhz does not make a huge difference. I'll try them both. What I can say is that 1Mhz as other constraints (I had to compile my own bootloader, then it is difficult to have reliable serial communication faster than 9600bauds, including for uploading sketches, meaning an update in the boards.txt file). Anyway, for sure, I'll build the board and make tests very soon. In the worst scenario, I may switch to CR123 batteries or LS14250.
@skywatch The issue I can see with steppers is that your camera might move when you poweroff the motors. As you said, when you poweroff them, they wont go back to center, but they also wont keep the position. If your camera is not perfectly balanced, it will "fall down". As well as your 3D printer : as long as you power the steppers, you can not move the axis, but as soon as you poweroff them (unlock) , you can move your axis.