As I have a fix for the missed reverse problem that Defender players sometimes suffer from I want to make the solution available to anyone building a Defender game based on a MAME system.
I can offer a USB encoder with either 18 inputs or 24 inputs, and using MAME standard keys or my modified keys (ALT,CTRL not used). Encoders have a micro-usb socket.
Note: The 24pin board with onboard earths is the neater solution if it fits, but I don't have a photo of it on a Defender panel.
I don't think I want to get into the business of selling general purpose keyboard encoders (and supporting them) so they are not offered as a shop. email me if you are interested and let me know what inputs you need. If you are doing something interesting like Defender+Tempest or Defender+Missile Command I'll be able to incorporate those controls too.
I use dupont connectors at the encoder and dupont or solder at the controls. I can supply the wires for that set-up.
£25 18input encoder and two earth boards, with dupont headers.
£25 24input encoder with dupont headers.
15p 40cm Dupont female to female. Use as is, or cut and strip ends to make 1 or 2 connection wires.
10p 30cm Dupont female to female. Use as is, or cut and strip ends to make 1 or 2 connection wires.
10p 20cm Dupont female to female. Use as is.
10p 10cm Dupont female to female. Use as is.