If you bought the LCD 12V 5A (A means Amp, a measure of current) switching power supply per the BOM, then you'll need to cut off the barrel connector to get to the wires. Or you could buy an appropriate barrel socket and wire to it. I cut mine. Using your meter, connect the black and red leads to the two wires (careful to keep
them separated to avoid shorting the power supply) and measure the voltage. If you see 12V, then label the wire connected to the black lead as - (negative, common, or ground) and the other as +12. Then remove the green power block with the 4 screw terminals (see image). With the openings of the block facing to your left, insert the - wire (the black wire in the photo to your left) into the bottom opening and the +12 (the yellow wire in the photo to your left) right above it. The two connectors above these are for a heated bed power supply. Verify the voltage 1 more time before you plug this block into it's connector on the RAMPS to ensure the right polarity (- to black meter lead, +12 to red lead and your meters shows ~12V DC).
If your motor comes with a 4-pin connector, odds are it's wired to be compatible with the Pololu stepper connector too. If not, then you will want to confirm via a vendor spec sheet or wiring diagram which wire is paired with the other (coil A and coil B refer to the image below). If you get it wrong, the worse case is your motor is going to act very strange, squeal at you, or just sit there. Pololu stepper boards expect a bipolar stepper motor with 4 wires and 2 coils. If you have a motor with more wires, it might could be used, and you will need to identify the 4 wires that connect to the start and end of the coils. The 0.1" pin connectors on the RAMPS are designed for matching headers. I like to buy the pre-terminated wires from Pololu and matching housings to make my own wiring, you can also salvage these from old PC's (all the front panel connectors for example). Whatever you use/find you want it to be a solid and reliable connection. The quickest way to kill a stepper driver is to unplug it while the power is on. The inductive spike with vaporize the traces inside the driver chip, thankfully with RAMPS, you can just buy and replace that driver board...not so with all-in-one boards.
|DRV4988 - test point circled|
If you need a fan on your hot end (like my E3D requires), then you will need to connect it to the 12V power. There is also a 12V header next to D2 that connects to this 12V too. For my printer, I bought a terminal strip so I could have multiple screw downs for 12V and ground.
|End Stop header on RAMPS. S is on top.|
Note: when I say labeled I'm referring to silkscreen legend printed on the RAMPS circuit board. There are multiple suppliers of RAMPS boards, they have all the same components but they may not have the same color shown.
If you've made it this far, we are ready to connect to the Arduino and send some Gcode.
I'm working on the next post and hope to have it out this weekend. it'll cover first test and calibration.