The basic flip-flop circuit or astable multivibrator (try telling a bunch of middle school kids that’s the name of this thing). This version was built after the Feltronics Flip Flop, but make so all the components could be used with feltronics. The negative voltage across electrolytic capacitors and the initial race condition meant that this was never the best first contact teaching tool, but that only inspired us to come up with something better. (ssh – this picture isn’t really a flip-flop, can you figure out what it really is?)