ST5 - Di2 - Retrofit Ant+/Bluetooth 

With the Bluetooth connection you can, for example, display the battery status or the selected gear in a riding computer (Garmin, Wahoo...).

It seems that the older ST5 (2018/2019) with charging socket in the bottom bracket area had an 'EW-WU111' Ant+/BT unit installed and thus mastered the connectivity. However, with the change of the control unit/charging socket to the right handlebar end on newer ST5s (from around 2021), the radio module seems to have been rationalized away.

You have to retrofit with a Shimano 'EW-WU111' D-Fly wireless unit for Di2 systems - ANT+/Bluetooth. You also need a Shimano 'EW-SD50' Cable for Di2 in the shortest version of 150 mm.

The 'EW-WU111' is connected to the free slot on the 'EW-RS910' on one side using the 'EW-SD50'. As this is a digital signal transmission, the 'EW-WU111' does not have to be "looped through". Simply plug the 'EW-WU111' into the handlebar and connect it to the 'EW-RS910' again.