12" I3V Build

[printbus]

What do I set "#define POWER_SUPPLY" to in the configuration.h file using this power supply?

The short answer is the POWER_SUPPLY definition likely won't make a difference to you. Unless you've added some power control mechanism onto the printer, that power supply and your printer will be on whenever there's AC on the power cord, and there's nothing firmware can do about it.

In at least older versions of Marlin... Firmware control of the power supply needs to start by having the printer electronics core always powered up, even when the printer power supply is off. The 12V supply on the printer is then used for just heaters, fans, and motors. ATX power supplies have a standby 5V output that often gets used for keeping power on the electronics. For non-ATX power supplies, you need to provide some other dedicated 5V source for the printer electronics. Power from USB is one way, at least until more 5V load like an ABL servo gets added. With that problem solved, then you have to identify an Arduino pin that can be allocated as the output used to control the power supply. This is done through the PS_ON_PIN definition in the pins.h file. If the pin definition is -1 (the default), there's no firmware control over the power supply and the POWER_SUPPLY definition isn't used.

When a pin has been allocated for the power control function, the POWER_SUPPLY value defines whether the control will be active low or active high. A POWER_SUPPLY value of 1 means a low logic level output will turn the power supply on, which is what you'd use if you're wanting to turn an ATX-type power supply on and off. A POWER_SUPPLY value of 2 means a high logic level will turn the power supply on, which would typically be used if you're using a relay to switch the AC power input to the power supply on and off. If using a relay, people are then often surprised to learn that they have to add a MOSFET or some other driver that can interface between the Arduino processor pin and the high current draw of the relay.

Only a few people bother with firmware control over the power supply. Some have wanted to turn the power supply on and off from the printer LCD panel. A menu item will appear for this once a pin is allocated for power control in the pins.h file. Some others have added remote print capability (typically with a Raspberry Pi) and want to be able to turn the printer on and off remotely as well.

Marlin has been undergoing some major overhaul over the last several months. I have no idea how much this changes in the newer versions.