3 ms·
In my opinion as an EE there would be some reasonably reliable ways to detect either a line or headphone connection. Headphone impedances are typically between
by sdk77 11y ago
In my opinion as an EE there would be some reasonably reliable ways to detect either a line or headphone connection. Headphone impedances are typically between 16 and 600 Ohms, and line impedance is typically in the 10's of kOhm range. That's one way to differentiate. There has to be an output signal (presumably audio) first, however.
Another way is to apply a very small DC current (that would certainly not damage headphones, so I would guess in the micro-ampere range) and check if there is continuity or measure the DC resistance of the load outright. For line inputs, as they're usually AC-coupled, DC resistance would be infinite, and for (DC coupled) headphones it is very low. It's an interesting subject and I wouldn't be surprised if there are some patents involved.
- jeff_marshall 11y agoDetecting AC vs. DC coupling would be obvious to a practicing EE, if presented with the problem, yes? I'm just a software guy with an electronics hobby and I think I could have figured that one out. That said, DC vs. AC coupling detection could probably be granted a patent if nobody had "disclosed" the idea prior to filing of such a patent, based on my experience with software patents. Sorry to vent, but patents on this sort of thing drive me crazy. I don't have any gripe with you or your post.
- sdk77 11y agoI did a quick search on google patents: https://www.google.com/patents/US9084035 https://www.google.com/patents/US9084035 - it uses a combination of AC and DC methods.
- qb45 11y ago> For line inputs, as they're usually AC-coupled Headphone amplifiers often have DC-coupled 10k potentiometer from input to ground with washer feeding a DC- or AC-coupled gain stage. So much for AC/DC detection. I think impedance measurement is used in practice. I can hear a quiet beep when I connect headphones to one of my laptops, for example.
- nibnib 11y agoA uA DC current can leak through a shitty AC-coupling capacitor, actually measuring the load is probably best.