Although we had a working dice prototype, to fully test our idea, we need to actually put a cube into the tray/reader. To achieve this, we need to get our breadboarded prototype inside a cube not more than about 4cm in size.
While we have access to surface mount PIC chips (16F628A in SSOP20 SMT package) with a total length of about 11mm and less than 1mm between pins, these chips are far too small to solder onto a home-made PCB by hand.
A slightly larger sized SMT chip is available (in SOIC package) but after investigation and trying a variety of PCB layouts, we discovered that using the standard SDIP (through hole) package requires a PCB that is only slightly larger than the one for SMT chips.
As a result, we've decided to stick with the slightly larger, but much easier to solder, through hole version of chips and components (hand-soldering SMT diodes is possible but can be tricky - using through-hole components for everything means almost anyone should be able to make a working dice PCB)
With all this in mind, we're making up some PCBs that will fit inside a cube, which can be used with the existing tray/reader board. The same technique will be used as for the tray reader, detailed in an earlier blog post.
Even using the larger through-hole components, the final PCB is small enough to fit inside a cube that will fit into the tray slots in the reader
The final, populated PCB, with through-hole components (PIC microcontroller and diodes) is small enough to fit inside a 4cm cube. Contacts on each of the six faces connect to the PCB/microcontroller using a number of micro-fine wires:
Green for ground, red for power, white for serial signals. It looks counter-intuitive because of where the components have been placed on the board, but if you follow the traces, you'll see it does actually match up with the schematics!