It is a long time ago, when I got Willem EPROM programmer. As the time is going quickly, someone could see this programmer is obsolete already. But there is simple, but big advantage of this device - low level modification possibility!
One of the requirement at the moment is decreasing supply voltage of modern chips. Therefore it is important to have ability of modern programmer to fulfill datasheet specification.
This is easy task for someone, who has access for schematics and basic skills in electronics.
But the basics for such solution is compliance with interface inputs. And with low supply volatge relates low input logic levels voltages. In this case 3.3V conversion (from and to) 5.0V is solved by this design.
The design is intended to build in reduction cover with supply cabel lead through side wall of the plastic cover.
You can see the converter schematics, layout and 3D simulation of PCB on the following pictures:
And Gerber & BOM files are here: