This is another part that I have. Its number is S7275-1 and I did not found any datasheet for it.
The circuit being more complex I just tried it without modification at 5 volts and to my surprise It is working. I then tried an unmodified one like the first one and it is working too at 5 volts. Same crisp and clean trigger.
For the usage of this part, as I understand it now, the CNC software keep the photointerrupter dedicated parallel port pin high. Since its output (of the part) is floatting when not trigered, the port pin stay high. When triggered, It connect the ground to the port pin forcing a low witch indicate to the software to stop everything. Does it make sense?
Alain