Hello Mr. Tim Olsen,

There is an excellent article describing a
Single board computer by Mr. Steve M. Taylor at the following web site http://www.8052.com/forum/read.phtml?id=17656.

There you will find some information on how to interface switches.

At the following web site you will find a data sheet describing the H21A1-A3 Slotted Optoswitch, 4 Terminal Transistor. There is also some more useful information about this device at this site.

http://dspace.dial.pipex.com/isocom/h2...tm#package

Good luck,

Charles Bannister