The Project:To see if I can build a Hard Disc on to the Electron (Again!)
As it turns out I didn't etch the board but a few years ago I passed on the project to a keen Electron user.
I haven't got round to etching the board yet!! one day...
A couple of months ago I have finally got round to etching a Host Adapter circuit board, I tried using a new 'iron on' method to put the overlay tracking on to the copper clad board but it didn't work out very well. I'll do it again with the tried and tested photo etching.
I've concentrated on the 1 MHz Bus and found that my original Circuit Diagram had a few errors
and was incomplete.
I downloaded a Schematic and Layout program called 'Eagle' from the internet which is ideal for producing a new Circuit Diagram and PCB layout. I have re-drawn the circuit so hopefully it should be correct now. If you want to look at it just click here.
Next on the agenda is the PCB for the 1MHz bus.
Looking on the BBC Lives web site uncovered documentation on how to build a Hard Disc for the BBC/Master series computers. On comparing this with my own documentation they were remarkably similar. The only differences were the PCB artwork and no CCT Diagram.
The artwork is good so I'll probably use it to make a PCB - there were a couple of errors on the placing.bmp which I have corrected here. R7 and R8 labels were transposed, and the 5V and 12V labels were also transposed.
The CCT Diagram I have is printed onto A0 paper so it's a bit large to scan. I have redrawn and saved it as a jpg file. Ideally it should be printed on A2 but it is readable on A3 (or two a4's)
The 4Gb HD is proving a little problematical as it is set to 512 sectors and not the 256 as required by the ADFS, on the old disc controllers it was a simple matter of changing a link but on this one it is stored in the drives Bios. The documentation is available for the drive but it will some time to decipher it....
The Date:A little later on 24/04/01
I have unearthed a 4Gb SCSI Hard drive that has the same interface and command
subset as the older OMTI 20C/ST251 combination. This will make it a lot easier to build.
Drive type: Seagate ST15230N
This should prove interesting...2Gb disc space on an Electron!!!!
The Date:24/04/01 The Start:
What is required:
A Plus 1
A Disc Interface i.e. Pres +3 or Slogger Pegasus
A Acorn ADFS ROM
A 1 MHz Bus
A Host Adapter
A Disc Controller
A Hard Disc
Hard Disc Utility Software
Kind of obvious...
The Plus one cartridge slots are required for the Disc Interface and the 1MHz Bus
I hope to borrow a Slogger Pegasus soon...If a picture appears then I've got it...
Acorn Electron ADFS ROM
It has to be an Acorn ADFS ROM and not the Pres ADFS ad Pres removed the Hard Disc entry points from it's version (v1.1)1MHz Bus
Required to interface the Electron to the Host Adapter.
I have a circuit diagrams for the 1Mhz bus, a patch board and cartridge to build it into. Initially I'll test the disc setup on a BBC B+, and if successful I'll go the final step and build the 1MHz bus.
This interfaces to the 1Mhz Bus and the Disc Controller card.
I have the circuit diagrams, board overlay and track layout. At the moment I am trying to source a circuit board, if I'm unlucky then this might be what kills the project - it is quite a complex board and would take a lot of effort (or money) to produce one...watch this space.
This interfaces to the Host Adapter and the Hard Disc. The controller I have is a OMTI 20C manufactured by Scientific Micro Systems Inc.Hard Disc
The Hard Disc Plugs into to the Disc Controller. The Drive I have is a Seagate ST 251, 40Mb. From past experience once formatted to ADFS I will be left with about 20Mb. More than enough for any Electron!!!
Back in 1994 when I first did this I wrote an article for the Electron User Group (early disc version) describing the whole process - when I get a chance I'll add some links to this site.