I've benefited from these two simple upgrades to my CT15, and have put them together here for ease of reference:
Adding BT to CT15/CT25:
https://www.festoolownersgroup.com/...-25-vs-ct-midi-and-ct-26/msg703351/#msg703351 (My version of implementation is at the bottom.)
Turning on or off the CT without pressing the membrane switch:
(The membrane switches, in my opinion (and in the views of those whom I've spoken to), are a downgrade from the previous knob switch because it's harder to turn on/off and it's subject to early wearing out. The suction power membrane switch is also a pain compared to the old dial.)
https://www.festoolownersgroup.com/...-on-off-switch/msg711094/?topicseen#msg711094
Adding BT to CT15/CT25:
https://www.festoolownersgroup.com/...-25-vs-ct-midi-and-ct-26/msg703351/#msg703351 (My version of implementation is at the bottom.)
Turning on or off the CT without pressing the membrane switch:
(The membrane switches, in my opinion (and in the views of those whom I've spoken to), are a downgrade from the previous knob switch because it's harder to turn on/off and it's subject to early wearing out. The suction power membrane switch is also a pain compared to the old dial.)
https://www.festoolownersgroup.com/...-on-off-switch/msg711094/?topicseen#msg711094