[01.14.2015] I designed a very simple $2 circuit board to breakout a “TRRS” (Tip-Ring-Ring-Shield ) 3.5mm headphone jack that you see all over the place these days. I’m wanting to drive multiple channels of an oscilloscope and the 3 RCA to 3.5mm TRRS cables seem to be in use everywhere and would be useful for low bandwidth ( ~50MHz ) applications for capturing digital state transitions ( not so much signal integrity ). The TRRS jacks exist in smart phones to support earbud head sets with microphones and also in video devices ( video iPod, camcorder, etc ) to deliver Left and Right audio plus a Composite video on 3 conductors plus a return instead of the normal “TRS” Tip-Rings-Shield 2 conductor stereo connector. Digging into to their pinout I was astonished to find out that mechanically all the TRRS plugs and receptacles seem compatible, but electrically EVERYBODY wires them up differently. The return signal actually isn’t the “S” ( shield ) for most manufacturers ( although it is for some ). The “S” is return for 3.5mm mono, 3.5mm stereo, but not necessarily 3.5mm TRRS 3 conductor. Some devices go in the TRRS order of “Audio-Audio-Ground-Video”, some “Audio-Video-Ground-Audio”, some “Audio-Audio-Video-Ground”. I looked up various TRRS to RCA cables on Amazon and about 1/2 the reviews said things like “piece of junk – didn’t work” or “audio on only one channel, no video” or “didn’t work until I plugged the red into video and yellow into audio jack”. What a disaster. How much does this cost Amazon in returns? Bad design decisions like these are made by electrical engineers and it really makes the industry look bad. I ended up going with the “Camcorder” ~standard~ as at least multiple manufactures agreed to it for video cameras ( but of course I won’t be able to use an Apple video cable ). I found a good writeup up on this whole TRRS mess here . To think electrical engineers helped get men on the moon in 1969.