[ I recommend the Emilio/Rizal 'Elf recreation' PCB - with the options below its a great development platform! ]
Elf Serial Auto-Keyer with Hex Keypad:
This combines both methods of input, either of which can be used to load programs.
Its a small plug-on removable unit that plugs onto pins mounted on the keyswitch header on the Emilio PCB.
When unplugged, the Elf behaves perfectly normally.
This zip file includes the Nano sketch and a brief PDF document with instructions & photos for the simple mods,
plus the 'bin' files for five demos, ready to transfer to your Elf. The bin files are:
'LED Flash' from the 1976 magazine, Decimal Counter, Hex Counter, Morse-code generator, and the Fernandos Hideaway tune: 'Auto-Keyer plus Hex Keypad' files (zip)
Elf Recreation Demo Loader...
Here's a video of a 'Demo Loader' that I made for the Retro Computer Festival.
Using only the Nano's inbuilt reset key for selection, it loads any of four demos into the Elf. It is connected in exactly the same way as
the keyer/hexpad and can be removed once a demo is loaded (or left in place):