Sorry for going quite. After a complete new install of this example provided on apple docs: https://developer.apple.com/library/ios/samplecode/EADemo/Introduction/Intro.html i had the chance to connect to the device.
Issues I learned:
- Triple check your protocol string.
- Do not modify the sample code until the first successful run.
- Do not forget to enter the protocol string in the Info.plist with the key "Supported external accessory protocols" (and make sure it is the correct plist)
- Check your bundle identifier, when you want to start app when bt device connects. The bundle identifier has to be the same domain as the bt manufacturer.
I hope this makes troubleshooters aware, because the answers were in the docu link provided above from apple.