In the 1980s, a number of schools in the UK had BBC
computers. Naturally, quite a few devices were designed especially for
these machines. One quite common one was the Plotmate plotter.
The Plotmate is an A4 flatbed plotter made by a company called Linear Graphics. It looks like Linear Graphics have gone bust quite a while ago and I have no idea who owns the brand name now. The plotter uses a proprietary pen design rather than the standard HP-style. It has no mechanism for automatically changing pens (such as a pen-carousel, or a pen-rack).
I obtained one of these plotters as it was being chucked into a skip. It turned out to be working fine (there's not that much to go wrong), so I decided to use it as a basis for further projects as well as to play with it.
The plotter was designed to connect, via a standard 20-pin connector, to a BBC computer. There is no "intelligent" hardware within the plotter. Instead, there are two stepper motors and a solenoid that the computer controls directly.
The software to drive the BBC is contained within a ROM. The site http://www.strafom.force9.co.uk/bbc/hardware/ contains the file plotmate.zip which contains the BBC ROM and some utilities. As I don't have a BBC computer (or emulator) I haven't used any information from these files.
The plotter has a resolution of about a tenth of a millimeter, or around 250 dots-per-inch, which isn't too bad. However, for most pens the size of the pen prevents drawing with this resolution.