Flutterby™! : Making a mouse switch optical

Okay, thanks to some goading from Brian I solved my frustration. So, to hook up an optical switch for a mouse button on a "Microsoft Wheel Mouse Optical" OEM version, take off the two feet furthest from cord end of the mouse, unscrew those screws, under the two feet closest to the cord there are two plastic tabs, and the top comes off. Clip the aesthetic LED on top of the main board, and attach a 10 Ohm resistor (to give 60mA to the LED, about half of its typical, but plenty bright) in series with the IR LED to those leads, short lead of the IR LED to the pointed end of the LED symbol by the leads you just clipped. Pry free the board with the buttons on it so you can get under the switch you want. For the right switch (with the cord end away from you), the positive lead is to the inside. Take that to the short lead of the phototransistor, and the other side to the long lead.

The phototransistor is extremely sensitive. Ambient light will close the switch. A layer of cardboard, like the backing to the component bubblepack, will not dim the light enough. I have the pieces mounted in brass, and interrupted the gap with a piece of sheet brass to break the beam.

Note for those who'd try it: An optical mouse does not appear to make a terribly repeatable position sensor, but will work for me in conjunction with a stepper motor to catch gross errors.