I got a little more work done on the Psion 2 interface board, but I'm getting some spurious results on the input port, so I'll concentrate on finishing the output port tomorrow by adding the 2 H-bridge ICs to drive the Lego motors.
I dug out the robot arm and started testing it. This was built about 5 or 6 years ago, but never used in anger until now. The rubber band belts had dozed so I've replaced those and checked the mechanism for free movement. I need to add pulse and limit switches to it to finish it off.
The arm is holding a Lego satellite dish in it's grab in the photo.