Interface type: Kempston Joystick
Compatible wih: Spectrum 16K, 48K, +48K, +128K, +2, +2A/+3
This joystick plug to Spectrum via expansion bus.
Buttons: Spectrum kempton joystick only can have one button but this joystick have two. In fact there is only button; The difference within them is that one of them has a extra circuit to have "auto fire".
How it works: In the middle of the board there is a big point that it's connected to GND. This point is also connect to joystick box, which it has conductive paint. When we touch a button, we close the circuit of the 4049 chip to GND.