14 Oct 2014: First prototype partially tested with EOMA68-IC1t
Thanks to ICube Corp the 5V power and the Micro-SD card slot were tested and confirmed working by way of a successful board bring-up with the EOMA68-IC1t prototype. One other minor error was also found in the process, which was corrected in the Micro-Desktop prototypes: the BAT54S shottky protection diodes were found to be mirror-imaged and needed to be placed face-down. The boards have been shipped and will be tested fully with the EOMA68-A20, later this week.
11 Oct 2014: Routing rework
From the photographs yesterday it was noted that flood-fill on both TOP and BOTTOM layers was missing! Whilst connectivity of the first assembled prototypes should be fine, and there is a fully-flooded GND plane, it is highly desirable to have both TOP and BOTTOM unused areas flooded and linked to GND as well. Along with some minor re-routing, addition of plane connection vias and of course the mirror-imaging of the VGA connector so that it can go on TOP, a preliminary rework has been done pending verification when the first prototypes arrive next week.
10 Oct 2014: First prototype
First prototypes are back from assembly. They are still currently in Hong Kong, and are to be shipped back for testing shortly. First most obvious mistake is clear: the VGA connector PCB layout was mirror-imaged! This is easily corrected but requires around $600 for reworking. The remaining functionality will be fully tested before that happens, but these boards will be sufficient to go ahead with the crowdfunding campaign.
Also, note the addition of a Micro-SD card slot, since SD/MMC was added to the latest EOMA-68 specification it was considered a good idea to take advantage of that in this very small board. Micro-SD was used instead of full-sized SD because the part is already used on the EOMA68-A20 CPU Card. On that board the Micro-SD circuit is a known quantity, tested and proven already, and the supplier details are already known. It was considered expedient to not redesign the circuit or find other untested parts.
29 May 2014: First revision routing
The Micro Desktop PC is a cut-down version of the Mini Desktop and the PCB size is around 4.5 x 3.0 in with USB, Ethernet and VGA connectors overhanging the edge of the PCB by about another 0.25in.
Connectors are arranged as follows: Top left is Ethernet, then downwards comes one dual-stacked USB2 connectors and the VGA port, followed by a a standard 5.5mm power jack (2.1mm centre pin), Bottom right is the reset switch and along the bottom edge is a 20-pin Expansion Header (1.27mm). All connectors are TOP side, with very few components underneath.
In essence this is a very simple board. RGB/TTL conversion to VGA has been kept to an absolute minimum by having buffer ICs straddle the EOMA68 RGB/TTL outputs within a few mm. All other high-speed signals are differential pairs. The design is nearly 100% complete: the 3.3v, 5.0v and USB power planes need to be done and it is ready to go.