I was Reading about a guitar fx dongle that plugs into a Smone earphone jack. For a Samsung smone it has to have the capability called ??. This recognizes the device when it’s plugged in. Since the device must have power, apparently the earphone jack has to analyze the device when it’s plugged in to determine if it’s a passive device such as an earphone or if it needs power, such as the dongle.
I have been noticing this phenomenon lately. I plug an earphone into a smone (smartphone) or laptop, and I see a bubble pop up on the screen saying I plugged something in. With Windows 8.1, it asks me if it’s an earphone, among other choices. With the smone, it may not acknowledge, but if an app requires an earphone, it will ask for it to be plugged in, and knows when it is plugged in. The FM radio is one example of this.
Another thing that had a problem was when I tried to record from my Samsung Galaxy 4S earphone jack by plugging a digital voice recorder into it. The G4S would not recognize the voice recorder and kept playing through the speaker. I had to use a ‘Y’ splitter for two headphones, and plug a headphone in one jack along with the recorder in the other jack. Then it switched over to the jack. The conclusion is that if the plugged in device does not have low impedance, like an earphone, then the Galaxy 4S will not switch from the speaker to the earphone.
The earphones that come with most smones have four metal contacts on the plug, instead of three like the stereo headsets. The fourth typically goes to the microphone that is a blob in one of the earphone leads. It’s for hands free telephone calls. There are two sizes of jacks/plugs; the standard 3.5 mm or 1/8 inch plug/jack, or the smaller 2.5 mm jack. Both have the 4 contacts. It seems that most smones have standardized on the 3.5 mm jack, while the cheap flip phones and similar use the 2.5 mm jack. Both sizes have been used for many decades, with 3 (stereo) or 2 (mono) conductors.
