There have been many project to create a storage interface for ZX spectrum like SMART card, DivMMC, ZXMMC, DivIDE . .. .. ..
This version will firstly focus on make an DIY version for SD/MMC card that give you the ability to play all you spectrum game selected from a menu.
The design is simple an is the first or a series SD/MMC interfaces for other hardware platforms. Plans are for ZX81, Dragon 32, Oric, MSX.
This version will use a standard Kempston joystick interface, a Boot/menu ROM and the SD/MMC interface.
Target price for a complete system is less 150Nkr or €17. Depending on if it will be external or internal.
When ready, I hope to add this to the Harlequin project.
Principle is as following.
1.Boot from external 16KB ROM.
2.Read menu for SD card as present to user with choose to select program or jump to native machine.
3. Load file to memory from SD card
4. Create switch routine in ram and switch to program
Kempston joystick interface
Enable/disable boot ROM
Hope to find some volunteers to help with the code.
Sources for information: