I frequently need to build external hardware to control stimuli presentation or receive responses in a novel way. I’m interested in what peripheral interfaces (USB, parallel, etc.) researchers conducting psychophysics experiments typically use to communicate with custom external hardware (i.e. micro-controllers, custom input interfaces, FPGAs, sensors, etc.) when using PsychoPy (or any other similar package), and how communication latency is handled if the operation is time-sensitive.