External Mini-Podule carrier board for Acorn A3000 machines.
The Acorn A3000 is unique among Acorn's ARM systems in being able to accept both an 8 bit "mini" expansion podules common to the A3010, A3020 and A4000 machines, as well as a Eurocard-sized 16-bit podule as used by the rest of the Archimedes and RiscPC range.
While the mini-podule fits internally, the standard podule slot on the A3000 is merely exposed on the rear of the machine, able to accept a bare board but clearly designed for an expansion enclosure of some kind. The mini-podule interface is electrically identical to the standard podule interface, just with an 8-bit data bus instead of 16 bit (and a couple of control lines omitted). This carrier board is designed to act as a passive adapter allowing a second mini-podule to be attached to the external podule connector.
Because.
Though, more seriously, the main motivator for this is as an aid to developing and testing hardware. My A3000 is my only Archimedes machine, and it does double duty as both development environment and test rig. This carrier board will allow me to experiment with a second mini-podule expansion card without sacrificing the storage provided by my existing IDE mini-podule. Not to mention avoiding having to leave the lid off!
This carrier board is only really suitable for use with the A3000, as it is the only machine with an external podule connector. It technically would fit in a desktop system, but since it is shorter and wider (and with a minipodule installed, taller) than a standard 100x160mm podule, it will not have mechanical support and I do not recommend trying this.
Order boards from your PCB fab house of choice. Solder components to board. It shouldn't be too hard to figure out.
J1 is a 96-position DIN 41612 Eurocard connector, right-angle, board mount, with male pins. Only rows A and C (i.e. 64 of the 96 pins) are used, but a 3-row connector will also fit. Something like Amphenol 86094647113745ELF should do the job.
J2-J5 are generic 0.1"-pitch pin sockets. J2 and J5 are 1x17 pin, J3 and J4 are 1x5 pin.
J6-J9 are optional 0.1" pin headers to allow connection of logic analyser probes for debugging. Leave them out if you want.
Mini-podules need to be supported at the back panel. The mounting holes on the rear edge of the carrier board are intended for some kind of bracket that provides mechanical support to both the podule and the carrier board. Not sure exactly what form this will take, but some kind of 3D-printed contraption would work well here. Watch this space.
I hope it goes without saying, but building something like this does come with risks - you are exposing the sensitive internals of the computer to the cruelties of the outside world.
If you take sensible ESD precautions and avoid shorting anything out, it should be fine, but if you do manage blow up your machine with this, don't say I didn't warn you.