Here’s a neat little line-tracking car kit that’s widely available from the usual online sources. There are a number of variations around, but they all share the same essential control circuit.
It is a simple example of the most basic class of Line Follower Robots, using an op-amp comparator as the “brain” to take feedback from left and right light-dependent resistors to control left and right motors accordingly.
If you know someone just getting into electronics and looking for something a little more challenging than soldering an LED blinky, then this kit would be a great next step. It’s hard to get wrong, introduces a few more exotic components, and it’s usually available cheap enough to be a nice stocking stuffer. Most importantly - it actually works!
As always, all notes, schematics and code are in the Little Electronics & Arduino Projects repo on GitHub
And if you want to watch it go round a test track for 30 seconds, be my guest … ;-)