What is it?

This is a PCB to be mounted on top of an Arduino Uno (or similar), and allows easily connecting the Arduino to various components in a CNC mill (e.g. stepper drivers, limit switches, spindle controller, etc.). This shield is intended to be used with the Grbl software running on the Arduino, and the pinout of the shield matches the default Grbl layout.

The reason for developing this shield, instead of using an existing shield, is that this shield has filtering applied to the limit pins to allow more robust operation in a noisy environment (at Fablab Amersfoort, our limit switches were picking up noise from the parallel running spindle power wires). Also, this shield only breaks out pins, it does not include any stepper drivers as most others do (since we use big steppers that need big, separate stepper drivers, as shown on one of the images).

This listing is for a bare PCB only. See below for the components you will additionally need. If you are interested in a kit (board plus needed components) or fully assembled board, let me know and I'll consider adding an option for that.

Why did I build it?

At Fablab Amersfoort, we built a big CNC mill, which needed to be controlled. Originally, this used a bit of protoboard with screw terminals. Then I designed this board and milled the single-sided v1 version on a smaller CNC mill we have there. After a while, some connection broke down, so I improved the design to a v2 to be produced professionally.

I ordered some boards at Seeedstudio, but since the minimum order quantity for the PCB was 5 pieces, I have a few spare boards that I'm happy to sell.

Needed components

• At minimum, you will need some (stackable or normal) pin headers to connect to the Arduino: 2x 6-pin, 2x 8-pin.
• To connect to the CNC hardware, you will need some double row pin headers: 2x3 for spindle control, 2x3 for limit switches, 2x 2x2 for extra ground pins (e.g. for cable shielding), 2x3 for control buttons, 2x3 for cooling and a probe, 2x9 for stepper control.
• The limit switch pins are connected through a filter. There is room for a through-hole series resistor (R4, R5, R6), two 0805 SMD capacitors to ground and a pullup resistor (R1, R2, R3). I've had good experiences with a 1kΩ series resistor and a single 10nF capacitor, leaving out the others. To leave out the filter completely, solder a wire in place of the series resistor and leave out the rest.

Layout selection jumper

When this shield was designed, Grbl was considering to switch to a slightly different pinout in v0.9, to allow speed control on the spindle (which needs a PWM pin). At that time, it was not clear if the new pinout would indeed become the standard one, so a solder jumper was added to choose between both pinouts.

By now, the new pinout mis final and used by default. To use it, connect the middel and terminals of the solder jumper. This connects the Z limit switch filter to D12, so you can connect the spindle control to PWM_SPIN (connected to D11). You should not use EN_SPIN (I would recommend not soldering pins to it). For the old layout (for use with Grbl 0.8 or before), connect the solder jumper to the left and use EN_SPIN instead of PWM_SPIN. If I ever build a new version of this board, the solder jumper should probably be removed.

Also see the Grbl documentation for further details.

Silkscreen error

Note that these boards have a small error in the silkscreen: PWM_SPIN and DIR_SPIN were accidentally reversed. I've corrected this on a small label, as seen in the image.

Specs

• Dimensions: 68.5mm x 56.6mm x 1.6mm
• Weight: 13g
• Design license: CERN Open Hardware License