Electronic Engineering Blog

Jim or Bob?

I’m working on a new interface board for a media system dock.

The dock is part of a multi-room audio system I have been working on for a major client. It’s a great system, lets you listen to any audio source in any area/room, and keeps all the wiring tidied away in a cupboard or some other out of the way area. The dock allows you to connect Apple devices such as iPhone, iPod or iPad and makes their media library available to the whole system.

I can’t go into specifics of the protocol used to connect iOS devices due to Apple’s licensing restrictions, but I can say this: Until the iPhone 5 came out, all apple devices used a 30-Pin connector and spoke a protocol called ‘iAP’. Accessing the media library on these devices was pretty straightforward and didn’t require a lot of horse power or memory. With the advent of iPhone 5 and the new ‘Lightning’ connector came a new protocol, known as ‘iAP2’. This new protocol is really very good. It is much more suited to todays media libraries and allows control of the device, communication with apps, audio out and so on.

My dock uses a USB connection to chat to the iPod and yet is small enough to fit into a single-gang UK wallbox – so it’s small! It uses a Microchip PIC32 processor and talks both iAP1 and iAP2 so you can connect almost any Apple Device to it.

However the new protocol handles the media library in a totally different way. It expects the host to hold a copy of the library and not make constant queries of it. This requires memory and what with it’s externall comms, USB Audio and USB Host stacks running on the PIC32, there wasn’t enough left over to cache an entire library of track, album and artists names, along with playlists and artwork.

Since the dock uses digital audio, it also has a companion interface that allows you to bring out Line Level audio on standard phono (RCA) connectors. We call this companion interface the Break Out Box, or BoB for short.

In order to buffer the media library we needed more memory. Now, I could add more memory inside the main audio processor, but there are hundreds of them out there and I don’t really want to go to every customer site and replace hardware, so I designed a new interface, it’s just a memory interface. So I call it ‘JiM’. It sits between the dock and the audio processor and buffers the media library.

So there we have it. BoB and Jim.

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