KENWOOD car player - control from steering wheel

Hi there,
That DIY is dedicated to Kenwood KDC-6051U or how to use your steering wheel audio control buttons to take control over it.
Based on specs, the unit should accept commands on cable. That sound great, but there is bad news also - there isn`t any info about the protocol used(or at least I can`t find one). On the market there are products(of course from KENWOOD is the first option) that read your steering controls and put necessary codes to the unit. That cost about 60e for the box and 25e for cable in KENOOWD one, and little less for the other brands. That is quite a lot if the whole unit cost 170e.
From what I check on that “communication” cable constantly come +5V. There is no action if I tight it to pot and try different resistance. Well, obviously is not PIONEER/SONY way. My shot in the dark is that they use single wire protocol by pulling to GND that line in certain amount of time to generate start - 0 / 1 - end sequences, but to be sure I have to buy one ready and to check what is doing so it isn`t how will be for now.
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