I made one of these years ago. I found it in the bottom of a pocket in my camera bag the other day. It still works! The thing is it has a Vivitar male jack on it so I can only use it with that flash. I vaguely remember that the schematic was in a magazine article. This would have been 25 or 30 years ago.
Anyone remember the article or have a copy of the schematic? I remember that it was very simple and had few parts. The one I have I installed in a pen cap.