The 7812 will give a stable constant output of 12 volts provided the input to pin (1) is 14 volts or slightly above. Its OK to mention voltage but it depends on what current is being passed through any of the devices mentioned, as anything exceeding a constant .5 amps (500ma) being drawn, really requires a small clip on heatsink to be fitted to the regulator to assist with its cooling. (for reliability)