June 2004: A LEGO rotation sensor for RCX is not so easy to find, and not at all cheap. In many cases it’s not the best way to control the absolute position of a part of a robot, such as legs, arms or other moving parts. So I came up with this LEGO angle sensor, after having visited many web pages, including Michael Gasperi’s page. Since I’m an electronic geek since I was 12, I had in my electronic workbench some tiny variable resistors taken from an old VCR.
I solved the problem using a square part of a PCB (bachelite board for electronics). The pin allows perfect compatibility with other LEGO elements, and it does not come out if you try to pull it (for example, to remove a gear), because the PCB square blocks it. The pin, coupled with trimmer, can swing about 270 degrees. The schematic is shown below.