After re-reading Wilf’s BEAM Heads 101 I had the urge to make another head. I also wanted it to have more “presence” that my previous heads, which meant that it had to be more obvious when it turned around, and hence less symmetrical. I happened to have some parts lying around that I could use to make such a bot.
A defunct laser disk player provided the motor and gears; it’s the assembly that flips the read head from one side of the disk to the other. A nice large solar panel allows the bot to run under reasonably bright indoor lighting, and the usual pair of photodiodes are tucked under the solar panel. The base is a chunk of steel that held the head magnets on a big old hard disk, and is heavy enough so that the whole thing doesn’t fall over.
The circuit is the basic power smart head circuit, with a Miller solar engine. Since I was using a separate SE, I could gang two sets of three inverters each to drive the motor. I actually used a 74HCT240 by mistake (meant to use an HC240), but it seems to work pretty well anyway!