Electronics Help

Hello, I’ve started my MPCNC build, and am waiting on some nylon lock nuts for the screws, so while I’m waiting for them to come in, I thought I’d mess with the electronics a bit. I was able to setup and flash marlin firmware onto my board ok(hardest part was getting windows 7 drivers to finally install). There is a section that is way over my head, as I’m not an electrician at all. This section below, can somebody break that down a bit for me? I am at the point where I have the lcd hooked up, the screen reads out OK, firmware is updated, etc. But I don’t have the steppers wired up(just ordered wiring kit today). I don’t want to fry anything, so not really sure what all this below means. Do I need to get a meter and use it to test some stuff? Do I need to turn the screws down so my servos don’t get hot basically? I’m a bit past the point of the square build on the first picture, really need to wait to get lock nuts, and the 2nd picture shows my screen lit up after flashing firmware.

Thanks for any advice!

Adjust the potentiometers according to your stepper spec sheet (a good place to start is 0.7V, any higher and you will need a fan on the heatsinks). The following video gives a very technical walk through on driver current. For the DRV8825 the quick and dirty formula is set the voltage between the potentiometers and the power ground the 90% (to cut down on the heat a bit) of half the rated current for your steppers. Voltage at the pot=.9*(stepper current/2).

What parts are you using? Specifically the drivers and motors? Did you get the from vicious1?

Its look like you have drv8825 If you buy from Ryan they already set up If you buy it somwhere else you need multimeter and you need to adjust voltage on theme before you connect stepers .


I do have the DRV8825 from this kit: https://www.aliexpress.com/item/3D-Printer-kit-1pcs-Mega-2560-R3-1pcs-RAMPS-1-4-Controller-5pcs-DRV8825-Stepper-Motor/1936434584.html?spm=a2g0s.9042311.0.0.CdRv9d

The steppers are from here: http://www.ebay.com/itm/US-Ship-5pcs-Nema-17-Stepper-Motor-Bipolar-84oz-in-59Ncm-4-lead-3D-Printer-CNC-/282030304065?rsta=en_US(en_US)&cnac=US&mail=sys&e=op&unp_tpcid=email-receipt-auction-payment&ppid=PPX000608&calf=8b3193521112a&calc=8b3193521112a&pgrp=main:email&unptid=5e173c9a-68b7-11e7-8d30-8cdcd4b6f248&mchn=em&t=&s=ci&page=main:email&cal=8b3193521112a&cust=GFPZUT7HSQZA2

Thanks in advance!

set up drivers to 0,7 I don’t think so that you need more on this motors.

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Kryzstof is right. 0.7V from the screw to ground should be right. You should get a multimeter, it will be useful all over the place. You don’t need an expensive one, but just going by warmth will not be fun.

Did you watch that popolu video (where she says “motors” funny)? I usually put the black cable on the incoming negative terminal, then put the red on the screwdriver that’s touching the screw. It’s a very small turn to move it a lot. Anywhere from 0.65V to 0.75V is fine. I would do it first with the motors unplugged, to get it close, and then plug in the motors, move them with the LCD (so they are on, they will resist turning) and do it again.

More than one person has come back with a “crap, I shorted something and burnt my Arduino” when doing this. So be careful with your screwdriver, please. But it’s not rocket surgery.



Jeffeb3 is erm pointing at me on the "crap, I shorted something and burnt my Arduino” Just be really careful you don’t touch 2 pins at the same time on the driver with ONE of the Meter Probes, it will damage components on the Mega if you do, for me I fried the 5v Regulator on the Mega.

I have no electronics experience or CNC experience but everyone on here will get you through the build just take your time and don’t rush the electronics side (Jeffeb3 and Ryan have been helping me a lot and there patience is excellent :-))

I too have the DRV8825 and the 84oz Nema 17s and as Kryzstof and Jeffeb3 has said set them to 0.7 and you should be fine.

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Thank you all, that’s the information I was needing. I still need to try and find the black contact point, as I was using usb power, but I’m more confident I will find it now. Thank you for telling me the points, was embarassed to ask.

I’m pretty sure you have to use 12V power top assist the drivers.

Use power supły that you will use on machin, If you dont have that just wait. Its 5 minut to set it up and 5 sekund to destroy it If you will be not cerful.

check If you have all jumper under stepstick you shudl have 3 for 32 steps. To masuje it correct you shudl have Arduino ramps and all stepstick that you will use . Screen and all cabel take off. Connect power supły to ramps. connect black cabel from multimeter on negative conector from ramps(Where you connect powersuply. Red from multimeter take some wire and hook around small flat scredriver set multimeter to =volts not ~volts and put scredriver with red cabel on screw on stepstic you shudl see somthing around 2,5V turn slowly scredriver to get 0,7 maby you need change devider on multimeter to get better riding. The Chines stepstick from Ali are little tricky to set up you need to make very small turns. And Thats all!


If you still fit unsure I can make movie exactly with ramps and dv8825 and how to adjust it

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I’m trying to get the voltage set, but having issues. i am powering my board with a black ac/dc adapter that plugs into the wall, then plugs into the round power port. If I power it this way, the screen just blinks on and off each second, and the yellow light blinks on and off each second. It works ok if I have usb hooked up. I have already flashed firmware also. But I do not understand which point to put the black meter probe to, as different videos show different points. Most of the pictures I’ve seen have a separate open power supply with wires going to the 4 terminal green block, which I don’t have mine setup that way. I know red goes to the screw, just needing a good point to put the black to. I’ve tried different spots, and have gotten different readings, I"m not sure which is right. I have tested an “AA” battery to 1.55 volts, to ensure that I’m using the meter correctly. Any ideas? Should I test voltage off of usb power at this point, or try and get the power supply working by itself before testing voltage?


My power supply is ac/dc adapter JCY-1250 12v/5A




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