The brightness issue is a bug that we have already fixed and will be included in the next firmware release.
The changing IP is because you have not set a static IP: the easiest way to do so is to use your router’s DHCP reservation (also known as IP reservation) feature to allocate a fixed IP for OpenSprinkler. This way the IP won’t change across power breaks.
Adding a external switch is fairly easy to do. In fact, since the sensor port now supports multi-functions (i.e. can be set as rain sensor or flow sensor), it’s easy to add a third functionality that makes it a trigger switch for a particular sprinkler program. This would require the user to set a program that’s associated with the switch. The current manual start program feature (i.e. use buttons on the controller to start a program) is more general, and allows you to start any program using buttons. I understand that this is not ideal in cases where the controller is locked in a waterproof box. We will consider adding the third function for the sensor port as described above.