The latest evolution of the RFM12 module is a mini version using an AVR TINY861
Design files are on AVRfreaks.
This is it, top and bottom
White connector on the left (3-pin) gets used as a one-wire port, its +V, GND and a port-pin
The other white connector is +V, GND and 4 analog i/p port pins
Also sporting a 6-pin programming header + LED.
After-all, its not really electronics if it cant have a flashing LED.
Schematic as shown, or a PDF version here
Boards are fairly compact, 35mm square.
The PCB's were produced in Kicad and manufactured by Seed Studio's PCB service.
These work well when paired with a solar charger + L-ion cell. The charger was an offshoot from the solar garden lights , also on the blog.
The small board on the right of the picture is a single-cell Lipo charger.
Its used here with one of the Tiny861 RF nodes (above). The charger board, as well as supplying the battery voltage to power the node, also gives out monitoring voltages (resistively divided) for the panel and battery voltages.
Charger is here