A general repository for learning and planning the development of CNC machines using a range of off the shelf and custom electronic and software solutions.

Originally purchased October 2020 from Amazon.

HiLetgo 2pcs A4988 V3 Engraver Drive Shield 3D Printer CNC Drive Expansion Board for Arduino 3D Printer CNC

The original development blog for the CNC shield can be found here.

Some basic code can be found here. I suggest using this code only to identify the pins on the CNC shield and inputting those pin values into your own script, built from the TMC2208 examples.

A better hardware explanation of the CNC shield can be found here.

Originally purchased October 2020 from Amazon.

TMC2208 V3.0 Stepper Motor Driver Module with Heat Sink Have UART Mode Compatible with Ramps1.4 or MKS Board SKR V1.3 for 3D Printers(Pack of 5pcs) (UART)

Originally purchased October 2020 from Amazon.

YOTINO Bipolar Stepper Motor Cable,4Pcs x 1000mm Long XH2.54 4pin to 6pin NEMA 17 Extended Connector Cable for RepRap 3D Printer CNC Machines

Anet Stepper Motor 42SHDC3025-24B

The stepper motor was salvaged from Jeff's original ALUNAR Anet A8 purchased in May 2017 from Amazon. The motor is known to have a non-standard wiring pinout and cannot be plugged directly into the V3 CNC Shield using the stepper motor cable.

Figure XX: Anet stepper motor 42SHDC3025-24B with wiring diagram.

Table 1: Anet stepper motor 42SHDC3025-24B with aftermarket stepper motor cable wiring table.

Refer to both the image and table above for the specific wiring for the Anet stepper. If you're using a different stepper motor, be sure to check its specific wiring diagram before connecting it to the CNC Shield.

TowerPro SG90 (Generic Miniature Servo)

Wiring instructions for SG90 servo with the CNC shield:

https://www.youtube.com/watch?v=iEuP8GzCJwQ&ab_channel=AlgeriaDZ

https://www.youtube.com/watch?v=GzPTYpOC8Ew&ab_channel=OddJobsWorkshop

1. Install the CNC Shield on top of the Arduino UNO.
2. Install the TMC2208 into the CNC Shield. Orient the TMC2208 such that the enable pin ("EN") on the driver matches the enable pin ("EN") on the CNC Shield.
3. Install the heat sink on the TMC2208 if it is not already installed.
4. Refer to Table 1. With the CNC Shield oriented upright, so the text on the board is legible, connect the stepper motor wires to CNC Shield in the order A+, A-, B+, B- following the configuration of the aftermarket cable. This will likely require additional jumpers or modifications to the existing cable, as the order will likely be wrong.

Note to Self: I removed the existing 4-slot dupont connector on the cable and used my 1-slot dupont connectors to separate the cable into four individual wires. This way, I can make my wiring connections as desired.

Script: TMC2208 with V3 CNC Shield/TMC2208_Example/TMC2208_Example.ino

The TMC2208 driver has a library within the Arduino IDE with provided examples. Version 0.2.5 is latest at time of this README. The INO file TMC2208_Example.ino is a modified version of the example code from the TMC2208 Arduino Library.

For this file, connect your stepper motor and stepper driver to the Y-Axis of the CNC Shield.

https://github.com/grbl

You must edit the following files in your library in order to get the correct behavior of the SG90 servo. By default the TCCRB timer on the arduino has a PWM which is wayyyy too fast for the SG90 servo. By changing the onboard timer prescaler, we can achieve a slower PWM which actually works with the SG90. Check out this link to show the available prescaler settings. Then, make the appropriate edits in the spindle_control.c file. Or, I have captioned the prescaler settings below from the forum responder EliteEng con Jan 9, 2014:

The per scaler of timer2 is currently set to 8 ( 16MHz / 8 = 2MHz )

Other per scalers available on timer2 are 1,8,32,64,128,256,1024 ( data sheet pg 162 http://www.atmel.com/Images/doc8161.pdf)

Setting Divisor
0x01 1
0x02 8
0x03 32
0x04 64
0x05 128
0x06 256
0x07 1024

Change the setting value of line 76 in spindle_control.c

TCCRB_REGISTER = (TCCRB_REGISTER & 0b11111000) | 0x02; // set to 1/8 Prescaler
^

The main directory grbl library is as follows on Windows: Documents\Arduino\libraries\grbl

First, ensure variable spindle is enabled in the config.h file. This allows D11 to act in PWM mode. In Jeff's original installation, this was already enabled by default. Still, I am including this below.

Documents\Arduino\libraries\grbl\config.h

// Enables variable spindle output voltage for different RPM values. On the Arduino Uno, the spindle
// enable pin will output 5V for maximum RPM with 256 intermediate levels and 0V when disabled.
// NOTE: IMPORTANT for Arduino Unos! When enabled, the Z-limit pin D11 and spindle enable pin D12 switch!
// The hardware PWM output on pin D11 is required for variable spindle output voltages.
#define VARIABLE_SPINDLE // Default enabled. Comment to disable.

Then, change the timer prescaler to get the desired, slower PWM for controlling the SG90 servo. Documents\Arduino\libraries\grbl\spindle_control.c

Original:

    #ifdef VARIABLE_SPINDLE
      // TODO: Install the optional capability for frequency-based output for servos.
      #ifdef CPU_MAP_ATMEGA2560
      	TCCRA_REGISTER = (1<<COMB_BIT) | (1<<WAVE1_REGISTER) | (1<<WAVE0_REGISTER);
        TCCRB_REGISTER = (TCCRB_REGISTER & 0b11111000) | 0x02 | (1<<WAVE2_REGISTER) | (1<<WAVE3_REGISTER); // set to 1/8 Prescaler
        OCR4A = 0xFFFF; // set the top 16bit value
        uint16_t current_pwm;
      #else
        TCCRA_REGISTER = (1<<COMB_BIT) | (1<<WAVE1_REGISTER) | (1<<WAVE0_REGISTER);
        TCCRB_REGISTER = (TCCRB_REGISTER & 0b11111000) | 0x02; // set to 1/8 Prescaler
        uint8_t current_pwm;
      #endif

Modified:

    #ifdef VARIABLE_SPINDLE
      // TODO: Install the optional capability for frequency-based output for servos.
      #ifdef CPU_MAP_ATMEGA2560
      	TCCRA_REGISTER = (1<<COMB_BIT) | (1<<WAVE1_REGISTER) | (1<<WAVE0_REGISTER);
        TCCRB_REGISTER = (TCCRB_REGISTER & 0b11111000) | 0x07 | (1<<WAVE2_REGISTER) | (1<<WAVE3_REGISTER); // set to 1/8 Prescaler
        OCR4A = 0xFFFF; // set the top 16bit value
        uint16_t current_pwm;
      #else
        TCCRA_REGISTER = (1<<COMB_BIT) | (1<<WAVE1_REGISTER) | (1<<WAVE0_REGISTER);
        TCCRB_REGISTER = (TCCRB_REGISTER & 0b11111000) | 0x07; // set to 1/8 Prescaler
        uint8_t current_pwm;
      #endif

After these changes are made to the GRBL library, recompile and reupload to the arduino using your preferred IDE.

GRBL Wiki Pages

Quick GRBL setup guide for Windows (Arduino G-Code Interpreter)

GRBL Arduino Library – Use the Arduino IDE to flash GRBL directly to your Arduino

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