Friday, January 10, 2014



We are almost there, we still need to connect the stepper motors, the cooling fan (definitely for the stepper drivers, and most likely for your hot end), connect the 12V power, and connect the end stops.

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).

Stepper motors
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.

Current limit
DRV4988 - test point circled
We want to set the current limit on the stepper driver. You will need a multimeter with the ability to measure a DC voltage, having a continuity check capability will come in handy too. Look at the Pololu product page for the driver you are using to see where the test point is and what the multiplier is. As an example let's assume you are using the DRV4988. Per the documentation the test point is a tiny via (a via is a metal plated hold that connects two or more copper layer on a printed circuit board) between the driver chip and the adjustment pot (short for potentiometer, AKA variable resistor or pot for short). The test point also connects to the metal center of the pot. You will need to connect the black lead of your meter to ground (aka negative, -, or common) and the tip of the red  lead touching the test point (aka Vref). With the power on, take a reading. Let's say you measured 0.34V. Per the product page Current Limit = VREF × 2.5, so our current limit is .34 * 2.5 or 0.85 amps. We want 1 amp (any higher and you just waste power as heat. If you need more current, then replace the motors with higher toque ones, you bought the wrong ones) so we need to set the voltage to 0.4V. The potentiometer on these boards are not that good, are fragile and are tiny so don't go nuts with the force you use to turn it. Now using a small slotted screw driver, slowly turn the pot clockwise (CW) while holding the red lead on the test point until you read as close to 0.4V as you care to (0.42 isn't a big deal). repeat for all 4 drivers (yes the extruder too).

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 stops
End Stop header on RAMPS. S is on top.
I mentioned these before, but to keep things organized I'll add it here too. The end stop wiring 3 home switches connect to the X+, Y+, Z+ connectors (which are to the right of the X-, Y-, and Z- connectors respectively) with the wires going to the top and middle pins labeled S and - retrospectively.
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.