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Having seen my System Keyboard in an Electron case somebody asked if it was possible to build an Atom into an Electron case ? So I thought about it and then did it !
The original intention for this project was for it to be built into an Electron case as Electrons are widely available and not too expensive whilst original Atom cases are very rare indeed and would demand a high price. However with the availability of a 3D printed Atom case design (see Stardot Atom Case thread) it seems many are building these boards into an Atom case after all so I have also produced a variant that will fit in an Atom case (though not an original case).
Perhaps these Atoms are more clones than replicas though ? They are functionally the same as an Atom, though I have made a few 'upgrades' to more available parts but tried to keep it in keeping with the original design:
the 24 2114 RAM ICs have been replaced by an 8K (video) and 32K RAM ('text' space)
the OS ROM is replaced by a 16K EPROM which has additional space for BASIC with Floating Point and DOS
the Utility ROM (e.g. for NFS) is replaced by a second 16K EPROM with links allowing selection from four different images (Issue V1.0 'Electron' Mainboards have a 2732 fitted)
the YPrPb outputs have been beefed up with the addition of a video driver
the Alan Knowles screen noise eliminator has been incorporated
'Electron Case' Variant
The 'Electron case' variant comprises a Mainboard that fits in an Electron Case in the space occupied originally by the Electron's mainboard, I managed to fit an Econet interface onto the board as well. An optional Floppy Disk Controller board (FDC) fits where the Electron power supply board was and also includes a GOTEK.
'Electron Case' Variant Replica Atom
'Atom Case' Variant
The 'Atom case' variant comprises a single board that includes the Floppy Disk Controller and GOTEK. It is not a replica of the original Atom as the board is the 'right way up' like a BBC computer.
'Atom Case' Variant Replica Atom
Keyboards
There are three variants of keyboard: the first fits in the place of the Electron Keyboard in an Electron Case. The other two variants are not intended to fit in an Electron Case but will fit in an Atom case. If you are not planning to build the computer into one of these cases then any of the three keyboards can be used.
The 'Electron' variant reuses the original Electron key switches (plus a few extra) , the second uses Cherry MX switches, so you don't need to scrap an Electron to build one of these ! The third keyboard uses BBC Computer key switches (please note this board is designed to accept the white Futaba switches, later types may not fit ?).
Here is a page with info on construction of the keyboards: Keyboard Construction
Memory Map
The memory map for the replica Atoms closely follows the original: Replica Atom Memory Map.pdf
EPROM images
Here are images that can be loaded into the EPROMs:
OSROM Image which includes COS/DOS/BASIC and the Floating Point Extension (16K position IC20-21)
Econet ROM a Utility ROM (4K position IC24)