Samsung Galaxy S4 Headphone Jack

May 15, 2013

The Samsung Galaxy S3 and S4 headphone output jacks are 3.5mm 4 pole jacks (TRRS) with the connections shown below at the left for the corresponding 4 pole plug where:
 L = Left audio channel 
 R = Right audio channel 
 Mic = External Microphone input/button presses
 Gnd = Ground (common) connection
The photo below shows the ends of an adapter cable from a Creative Technology 7.1 sound card used for testing the functionality of the 4 pole headphone jack under various conditions. If a 3 pole plug (e.g. a typical simpler headphone cable with no microphone capability) is connected to this type of 4 pole jack, the longer ground part of the 3 pole plug will short out the microphone conection in the 4 pole jack to ground. On the S4, shorting out the microphone connection in the jack enables use of the internal microphone of the S4 for recording with apps like the native "Voice Recorder". (In addition, temporary shorting of the mic/ground connection is recognized as a button-click command; see below). With the microphone connection completely open (NOT connected and not shorted to ground) there is a voltage of ~ 2.3 VDC (measured) between that connection and ground and the internal S4 microphone is disabled. If a resistance of 1.4kΩ or greater corresponding to the impedance of an external microphone (or a microphone and a preamplifier) exists between the microphone connection and ground, the internal microphone will remain disabled and the external microphone circuit is available for recording. Measurements on one S4 shows that the 1.4kΩ value corresponds to the DC voltage on the microphone jack pin dropping to 1.0 VDC. If the resistance between the microphone pin and ground is changed from above to below the 1.4kΩ value, the microphone enable/disable function will not activate unless the headphone plug is removed and reconnected. Similar results, but with a lower resistance threshold of 1.0kΩ have been reported for other Samsung smartphones.

Volume and Mute Encoding with the Headphone Cable

The headphones provided with the S4 include buttons for adjusting the audio volume and muting as shown in the picture below. Simple measurements show that the DC resistance of the headphone set between mic/ground connections on the plug with no buttons pressed is open (infinite resistance). When the mute button is pressed, the resistance is about 50 ohm (probably a simple series resistor in the headset wiring). Clicking of the volume-adjust buttons (either temporary or constant) shows a quick reduction of resistance and then a DC open circuit which is used to signal volume adjustment to the S4 processor. Based on these simple DC measurements, it is not clear if the volume button functionality is a momentary-switch design or if a capacitor/resistor combination is used:

See also External Mics on Galaxy Devices Just One Resistor Away