Sinclai ZX computers (ZX81/Spectrum) don't ship with a joystick port but they can count on the ubiquitous Kempston interface to provide 4 directional lines plus 3 buttons and that is more than enough to connect a Sega Master System HPD-200 paddle controller.
Paddle detection and reading code provided by SMS POWER. I/O address changed to match Kempston (0x1F), though.
A simple hardware adapter is necessary in between the Kempston interface and the HPD-200 paddle
An alternative for the HPD-200 is to build a DIY SMS/MarkIII paddle controller by Raphaël Assénat. In such case the wiring can be modified to route the signals from pins 5,7 and 9 thus dispensing the use of the adapter.
Example code (work still in progress) available at my github repository.