custom SBC

2 Articles

Version 1.8 of the 80386 ISA SBC in its assembled glory. (Credit: Alexandru Groza)

Building Your Own 80386DX ISA Single Board Microcomputer

March 30, 2022 by 36 Comments

Having grown up with 386-level systems during the early 90s like so many of us, [Alexandru Groza] experienced an intense longing to experience the nostalgia of these computer systems from an interesting angle: by building his own 80386DX-based single board computer. Courtesy of the 16-bit ISA form factor, the entire system fits into a 16-bit ISA backplane which then provides power and expansion slots for further functionality beyond what is integrated on the SBMC card.

Having started the project in 2019, it is now in the home stretch towards completion. Featuring an 80386DX and 80387DX FPU alongside 128 kB of cache and a grand total of 32 MB of RAM, an OPTi chipset was used to connect with the rest of the system alongside the standard 8042-class PS/2 keyboard and mouse controller. A large part of the fun of assembling such a system is that while the parts themselves are easy enough to obtain, finding datasheets is hard to impossible for some components.

Undeterred, some reverse-engineering of signaling on functional mainboards was sufficient to fill in the missing details. Helpfully, [Alexandru] provides the full schematics and BOM of the resulting board and takes us along with bootstrapping the system after obtaining the PCBs and components. After an initial facepalm moment due to an incorrectly inserted (and subsequently very dead) CPU and boot issues, ultimately [Alexandru] gave up on the v1.6 revision of the board

Fortunately the v1.8 revision with a logic analyzer led to a number of discoveries that has led to the system mostly working, minus what appears to be DMA-related issues. Even so, it is a remarkable achievement that demonstrates the complexity of these old systems.

A Custom Raspberry Pi Spotted In The Wild

July 3, 2021 by 21 Comments

Since the first Raspberry Pi came to market back in 2012 there have been a variety of models released. Some of them are rarer than others, and unusual boards can even be rather sought-after. This one spotted at a Thai junk vendor won’t be in the hands of many collectors though, and investigating it sheds a bit of light on some of the most unusual boards from the company.

The board is recognisably very similar to a Pi 3 with a BCM2837 SoC, but despite all that it has no Pi logo. On the underside there is an eMMC in place of the SD socket, and one pair of USB sockets has been replaced by a micro USB socket and a header. The source is reported to have been a washing machine, but given that this SoC is exclusive to the the Pi Foundation there’s no way it could easily have been manufactured by anyone else. The answer comes in the 2015 launch of a customisation service for industrial customers, which allowed manufacturers to have their own versions made of the fruity SBC.

From the point of view of an experimenter this board offers nothing that a standard device can’t do. But it’s an interesting glimpse of an unseen side to the Pi story, and it holds the prospect of other special versions being unearthed. If you find one on your travels, let us know!