Using the optical sensor from a ball mouse

[Jerson]

Luke

I suspect that you've forgotten to make the PIC pins as inputs using the TRIS registers.

[lsteele]

Hi Jerson,

You're absolutely right - that was the problem. What an incredibly stupid mistake! For anyone who's interested it now works fine with a 10k pull-down as in the diagram I posted earlier, or as in mackrackit's schematic.

Thanks very much,

Luke