Add relay control for softpower or failsafe mode

[aeakin1]

The request came in as a result of a Photonster hitting a bug in the board firmware. Due to this bug, the printer was rendered powered on and somewhat operational for an extended window, while the cooling fan(s) had been shut off due to said bug. This resulted in potential damage to the LCD, LED and Mainboard components due to potential overheating.

This feature can be built to operate in two mode, selectable by the user via a config checkbox and trivial wiring change (move 1 wire from the N.O. to the N.C. screw terminal ( or visa-versa on the relay board)

Safety shutdown mode

Safety Shutdown Mode puts a Normally Closed relay in line with the 12V power leads as they enter the chassis.

The ESParaSite can then open the relay (shutting down power to the Printer Mainboard).

Advantages

• The ESParaSite is only responsible for opening the relay (cutting the power).
• Printing can be aborted in case of over temperature conditions being reached.
• allows us to control the printer power remotely

Disadvantages

• less features
• If used for remote power on/off, the "off state" becomes dependent on the ESParaSite.

Soft Power Mode

Soft Power mode puts a Normally Open relay in line with the 12V power leads as they enter the chassis.

Advantages

• allows us to control the printer power remotely
• reduces eeprom corruption risk by allowing us to make clean writes and enter sleep mode rather than being at the mercy of when the user turns off the switch.
• allows us to cut power to the unit in case of over temperature conditions being reached.
• Could implement wake on LAN/Wifi and other handy features

Disadvantages

• Relying on ESParaSite adds additional points of failure and complexity
• Successful prints completely depend on ESParaSite stability