Take advantage of the NTC thermistor found on the Einsy as an additional
safety measure, following the steps of the other MIN/MAXTEMP errors.
Introduce two configurable params AMBIENT_MINTEMP and AMBIENT_MAXTEMP
in the variant defines and set them for the MK3/MK3S to -30/+100
respectively.
AMBIENT_MINTEMP is primarily intended to catch a defective board
thermistor (to ensure MAXTEMP would be properly triggered) and thus the
trigger temperature is set just above the sensing limit and well below
the operating range.
AMBIENT_MAXTEMP is set at 100C, which is instead 20C above the maximum
recommended operating temperature of the Einsy. The NTC thermistor is
located just above the main power connector on the bottom of the board,
and could also help in detecting a faulty connection which can result in
rapid overheating of the contacts.
As for MAXTEMP, we cut power to the heaters, print fan and motors to
reduce power draw. Resume is not possible except by resetting the
printer, since the user is highly advised to inspect the board for
problems before attempting to continue.
