Left to Right: CUMANA DISC INTERFACE, PROJECT EXPANSONS USER PORT, CLICK, ELECTRON GOMMC
It was so simple at the beginning. In 1983, the Acorn Electron was born, a small beige machine with 32K ROM and 32K RAM and games were loaded into it from cassette tapes. But that there expansion port on its rear got the creative juices flowing of every manufacturer out there, even those with only a passing interest in electronics.
Some expansions were quite obvious: joystick interfaces, disk systems, printer ports, etc. Others came about to try and redress some of the features of the BBC Microcomputer that were 'left out' of the Electron's design: RS423 ports, the 1MHz Bus interface, Mode 7 units, ROM chip holders, 4 channel sound expansions, etc. Yet more arrived as original firmware expansions: the CLICK organiser, the speech synthesis VOXBOX, the MODE 7 SIMULATOR ROM, etc.
In Hardware Land, you can see and read about every expansion we've ever picked up. Now, by this, we mean expansions that were sold by manufacturers during the Elk's lifetime. Many hobbyists built devices that put the Elk to quite bizarre uses. One Electron spotted on eBay, for example, had a digital clock burned into its lid. Another had a cartridge of drug store prices included. These strange variations are, obviously, not in our ambit.
What you will find though, is a dazzling display of peripherals that were released in very limited number. In many cases, you can also download a Microsoft Word version of the documentation that was originally supplied with that interface. However, as is the nature of second hand buying, that we have gathered the documentation is not always guaranteed.
If you have got an interface for the Electron for which you have no instructions then you may find them here. You can also use Hardware Land to gauge how popular or rare that interface is.