Making your own powerful Controller on the cheap side

Keep AC and DC side apart. Circuit GND on the DC side is V-.

As far as terminal block applies, I am not sure what you mean (I just woke up… :wink: )
This is how I use the terminal blocks in my controller:

Hey, sorry, yes, I meant a single terminal block that is all bridged. I’m other words, make one single block that is a star point where everything is connected to Earth ground and common (V-).


The way Phil designed it was to keep maintainability on the field simple. He did this type of design professionally. So each run had its own leg that way diagnostics were faster and simpler. His approach was influenced by his career but the design is solid. (Otherwise he would be out of a job).

Ah, that makes sense. Yeah, my amature brain (that constantly tries to simplify everything) couldnt figure out why it wasn’t all consolidated. But root cause analysis (RCA) as my field says is a great reason. Sounds like there is nothing electrically wrong with consolidating though.

Thanks all.

As far as grounding goes having everything consolidated on a single point (= star ground) is simple en effective against voltage differences on the GND plane.

I believe that you might be looking for Phil Johnson post about his CNC Demon Controller. it can be found here now,


Maybe there is an assumption on my reading this.

You should use a star implementation on the earth grounds.

You should use a star implementation on the V- negative returns

Earth ground and V- returns should never be connected together.


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In Phils schematic, it would seem that the PS GND, from the ground wire on the power supply, is tied to the Arduino GND and it is also tied to all the shields of the limit switches.

I don’t see the Arduino GND, -5V, connected to the -24V. I would have thought that the -5V from the Arduino and the -24V from the PS should be connected together… Maybe I missed it.

The -24V is used only for the fans and the drivers.

So is this not right? Having the Arduino and the line ground wire connected together?

TB4-2 (ps Earth ground) is connected to
TB2-5 which is bridged to
TB2-6 (PS ground) and
TB2-1 (Ard-gnd).

The question is, what is ps-gnd? I’m not using an inventibles ps, so I don’t know. Is it common (v-) or Earth ground? If common, I’m assuming 5v?

Grounding is almost a discipline into itself. When talking about “ground” you must be specific and consistent with your terminology in order for everyone to be on the same page.

The “third” prong of an AC outlet in the US is usually connected via a green wire and that wire becomes “earth ground” when you plug your device into an AC outlet. It should only have things connected to it that you want to be at “earth ground” potential. Examples would be the metal frame of an electrical panel, the “earth ground” of an additional power supply or the shield of shielded wires.

Since voltage is a potential difference you have to establish what the reference point is for the “returns” in the DC circuit (usually a black wire in the US) so different logic boards can talk to each other when various voltages are used in a device.

So when you hook up two or more devices you would hook their circuit grounds together, but never hook any of them to “earth ground”.

Hey Larry,

Yeah, this is what I have always thought. However, I know very little about electrical engineering, so trying to figure all this it from communities and research. Phil’s schematic connects all of the signal return voltage to Earth ground. There are also MANY posts I’ve read where people solve interference problems by connecting return voltage to Earth ground.

I don’t have a horse in this race, I’m just trying to figure out how to wire up my board…

I interpreted PS Ground as Earth ground, which is the green wire on a 3 wire line cord.

I wasn’t sure what was meant by that term. Phil had to go to extremes to get the electrical noise on his machine under control. I don’t remember if we discussed grounding issues at that time or not.

In any case, my controller is working very well, no noise issues, can home with no problems and never a carve stopped in the middle of the job. So I’m happy.

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I’m coming late to this party. I’m not sure how much these homebrew controllers end up costing. A company called Synthetos sells a controller that will drive 4 motors with a USB interface. It’s called the Tiny V8 and sells for $130.00. Just add a power supply and you’re good to go. BTW, I have no connection with Synthetos. I’m just a very happy customer.

Here’s the description

The TinyG project is a multi-axis motion control system. It is designed for CNC applications and other applications that require highly precise motion control. TinyG is meant to be a complete embedded solution for small/medium motor control. Here are some of the main features of the v8 hardware.

Integrated motion control system with embedded microcontroller (Atmel ATxmega192)
4 stepper motor drivers (TI DRV8818) integrated on a ~4 inch square board
Stepper drivers handle 2.5 amps per winding which will handle NEMA17 motors and most NEMA23s
Accepts Gcode from USB port and interprets it locally on the board
6-axis control (XYZ + ABC rotary axes) maps to any 4 motors
Constant jerk acceleration planning (3rd order S curves) for smooth and fast motion transitions
Very smooth step pulse generation using phase-optimized fractional-step DDA running at 50 Khz with very low jitter
Micro-stepping up to 1/8 (optimized DDA makes this smoother than many 1/16 implementations)

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I bought a G540. Its great. I also bought the Ethernet SmoothStepper board as I wanted to use ethernet instead of usb.
Runs all the motors great and allowed me to use Mach3.


yup best upgrade after all the obvious ones!

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I recently purchased the C25 - Smooth Stepper Terminal Board and it allows me to connect more motor controllers. Set up my 4th axis on it and All is well. Except I am trying to figure out why my 4th axis rotates incorrectly. It will rotate 3 times to a 360 degree command.
Did all the calculations and research and its still off. :confused:


3:1 gear train?

I have no experience with 4th axis but there is a motor step adjustment feature in Mach3

The internet has lots. (and I’m sure tutorials)
Everything is labeled (unless you’re talking about using the discreet chips).
Quick google search turned up this:

Grbl’s connections can be found on the GitHub site.

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