The LITTLE E3D2 is intended to be plugged to an another board with additional circuity, so is in this application. The Gear One the LITTLE E3D2 is plugged into is an inexpensive, single sided PCB. It contains connectors for interfacing the LITTLE E3D2 to the world (relay contact, RS232 interface and DC power). On the Gear One board is also buzzer, character LCD display connector, 4x4 keyboard connector and connector with raw UART1 signals used for communication with a slave microcontroller board. All of this is controlled remotely by a master system (in this particular case PC running Linux) over Ethernet network.

Note that the LITTLE E3D2 pictured here is in debug version with long headers. The board can sit on another one while all signals are still accessible (for instance for connecting a logic analyzer for debugging).

Quick and dirty pictures talk more than tons of text. Revision 2 of the Little E3D2 on the board named Gear Three. A modification with off board Ethernet connector, switching power supply and RS485 bus which is better suited for multi slave communication (for instance with remote sensors) than RS232.
Realtime clock for autonomous run, where keeping actual time is important. For instance for safely passing through power fails and not loosing actual time when the server becomes unavailable. The device can still gather data and send them to the master just after network goes up.

The Base One, single sided printed circuit board has been designed to show, how easily can be an application with the Little E3D2 module created. It is intended for development purposes and its function is powering the Little E3D2 and interfacing it with other prototyping circuity.

There are two voltage regulators on the board. A switching regulator based on MC34064A provides enough power for running most applications and allows the board to be run with wide range of input voltages either AC or DC with no overheating. A linear 7805 series regulator is here to provide a power source alternative for applications where its worse efficiency doesn't matter. The designer can select either supply for powering the Little E3D2.

Little E3D2's RS232 and RS485 signals are routed to appropriate connectors, while other signals are accessible on standard 2.54 mm pitch headers.

Because designers have different behaviors for prototyping (one uses non soldering arrays while other likes to solder everything on a PCB) we decided not to include a prototyping area on the Base One board.