Based on the scheme and explanation given on
Zimmers.net I have prepared everything to make a batch of this adapter.
View attachment 2448330View attachment 2448329
To do this I transferred this schematic to kiCad and then made a couple of changes, I added the 100nF capacitors (opconal) and also a small selector to send the 5v to pin 5 of the DB9 connector or to pin 7 of the same.
With the 5v on pin 5 the joysticks connected to this adapter would behave like a Sega Megadrive controller, my 8-bitdo pad works in this mode.
View attachment 2448331View attachment 2448332
The adapter will be delivered with a 3D printed case.
Tested on a Commodore Plus/4 and is also valid for the Commodore 16.
For more information, click on the link.
Plus4joy
The price of each will be 26€ plus shipping and PayPal fees.
Edit:
Your adapter is on its way