I started making my IR pen the other day. I collected all my supplies from my local electronics shop and put it all together. What I didn't know (because I didn't really read the posts) was that you needed a momentary switch for the pen. So after building this thing I had to take it apart to rebuild it correctly. Since I didn't have time to got to the electronics store that day, I started looking around to see what I could find for a momentary switch. Then I thought of a couple of old mice that I have stashed in a drawer. I ripped the mouse apart and soldiered to the board were three momentary switches that were small and easy to use. All you need to do is de-soldier them from the board and use them in your IR pen. I will try and post up some pics of the pen, but if you have some extra mice lying around, you can use the momentary switches out of them.
