12th January 2012
That 3.5mm phone jack! It’s on just about every mobile phone and is a standard size and pretty rugged, but it’s amazing what accessory you can plug in there and a smartphone will recognise it and adapt accordingly. It’s also a challenge for those like Wolfson on the other side of the socket!
People expect to plug in headphones, which have three terminals, and headsets, which use four terminals (one extra for the microphone). They might plug in a lead to connect to their car audio system or home hi-fi, or even a video cable. Then there’s those buttons on the cable. Is there just one? How many ways can you press it? Is it just for phone calls, or can it control music playback? Perhaps there are several buttons. How do they work through those four terminals? Do the buttons affect sound quality when operating?
The solution involves analogue and digital IC technology and software. Wolfson accessory detection has to be clever, so it is inaudible and can differentiate between headphones, microphones, video links and button presses - all without consuming a lot of power. It uses tiny, varying measurement currents with a high degree of precision, coupled to a digital control engine, to achieve this. This allows the correct signals to be activated and offer features like safe volume limiting on headphones, but not on a hi-fi connection, as this would reduce the signal level and make background hiss more apparent in a quiet room. And the combinations of uses keep on growing.
So next time you plug something in to that socket, do think of our engineers solving your problems behind the scenes.
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