Well, for a simulated 737 at least. via Hackaday:
[Andrea] didn’t want to dig around with the clunky point-and-click interface in FSX, so he created a virtual autopilot with a 2×16 LCD display and an Arduino to interact and set the most common autopilot settings such as altitude, speed, heading, and engagement. The physical interface is just three tact switches and a pot, while the interface to FSX is a custom driver that turns the USB out of the Arduino into actual flight commands.
Video at the link...
Comments
@Tom, funny headline for humor value... not universally appreciated apparently!
Sensational headline for attention. Thumbs down.
That's not an autopilot in the sense of the APM. That's a control interface for the B737 autopilot, like this one.