Comment on Can someone explain how this wiring works?
kkj@lemmy.dbzer0.com 1 week agoMy guess is that the original power button shorts its trace to ground and the console is looking at that resistance to tell whether it’s pressed. Adding a replacement button just means putting something that can connect that trace to ground on demand.
ChaoticNeutralCzech@feddit.org 1 week ago
Touch buttons usually work via capacitive coupling: they don’t check for decreased resistance but impedance (AC resistance), which means alternating voltage (often single-polarity, e.g. a 0/5 V square wave, to avoid the need for a negative voltage rail) is applied to them. While conductivity (inverse resistance) allows DC to flow or AC to flow in phase with voltage, capacitive admittance (inverse impedance caused by capacity like a nearby finger) allows only AC to flow, 90° behind sine voltage (proportional to change in voltage, which is 0 for DC voltage). A short to ground is the lowest resistance or impedance possible so if the system just checks for current flow (usually by monitoring voltage drop over a resistor) at any phase, like most touch sensors do, it will see a big current flow (maybe too big for some badly designed ones, so careful!) and register a touch. Some touch sensors use the body’s capacitance to complete an LC or RC circuit, in which case a short won’t work.