On 11/01/17 15:41, ixiz wrote:
Where can I find more information of what protocol Shimano di2 uses
to change gears I would like to add an additional switch so I can
change gears at the different hand position



I have no idea, but if I was to design such a system I'd investigate the
possibility of using CAN bus. A very similar tech is used for
automotive automation.

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JS