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Grbl CNC Firmware on ESP32


I have been working on this for months. I am happy to announce that it is finally working right. The ESP32 will be a great option for CNC. Here are some things I am excited about.

  • Fast – Two 32 bit Cores at 240MHz Each, FPU, 80MHz Timers
  • Memory – Tons of Flash and RAM
  • Low Cost – $3-$10 depending how you buy it.
  • Small Size – Not much bigger than an Arduino Nano
  • I/O – It has about the same number of pins as an Arduino UNO, which is the target for Grbl
  • BlueTooth and WiFi – This is great and actually the primary reason for my port.


The bulk of the code was very easy to port over, but getting very low jitter, step pulse timing took a long time to achieve. This is not my first port of Grbl. My first port was to the PSoC5. That was much easier, but this was my first major project on the ESP32.

A goal was to use the Arduino IDE to develop the code. I thought it would make the project a lot more accessible to novice programmers that just need to make a few tweaks. I also tried to make the code easy to maintain with Grbl. This means there a few throwbacks/workarounds to AVR port numbering. etc.


The ESP32 uses an RTOS (Real Time Operating System). While “real time” sounds perfect for CNC, it is not good for step pulse timing. An RTOS allows multiple tasks to run “at the same time” and it manages the priorities and interaction of those tasks. The RTOS switches tasks at a “tick rate”. The tick rate is typically about 1000Hz. This means each task gets at least 1ms of time and the others wait. You can designate a high priority task to prevent these interruptions, but some tasks have watchdogs that must be reset so you need to give them some time.  You can set the tick rate higher, but I need a more than 50,000 hz step rate. That is not practical for the RTOS. I can turn off the RTOS and/or the watchdogs, but a major appeal of the ESP32 is the WiFi and BlueTooth. These need the RTOS.


The normal Grbl way generate step pulse timing is to use interrupts. As long as you follow the rules for interrupts, they will interrupt the RTOS without any delays in very deterministic manner. The rules are about how much time you can spend in the interrupt and what things you can do in the interrupt. The interrupt duration was not an issue because the code in the interrupt only takes a few micro seconds. What you can do in the interrupt took a while to figure out. The ESP32 does a “panic” reboot when it does not like something. That happened a lot during development. Most of my problems were related to how I used the peripherals. Things like the RMT feature simply can’t be used.

My Dev Board

I designed a little Dev Board to help me with this project. The features include…

  • 3 Stepper Drivers
  • 3 Limit Switches
  • 1 Touch Probe connector
  • Mist / Flood Coolant outputs
  • Start / Hold / Reset / Door switch connector.
  • Spindle / Servo / Laser – Connector
  • SD Card – This is just a breakout to a header that can be wired into the CPU if I ever decide to do that.

Next Steps

Testing – I need to do a lot of testing. I tested most of the features along the way, but need to double check all the config options.

Clean up – I have a lot of commented out debug code that needs to be removed

Publish on GitHub – Done. GitHub Repo

BlueTooth – That is the first new feature I want to add.

Hobby Servo Features – I use them a lot in my small machines and 328P Grbl doesn’t handle them well because the lack of 16 bit timer availability. I want high resolution jitter free servos as an option for any axis.

Simple Kinematics – GCode can be converted on the fly to alternate coordinate systems. This would not consider joint dynamics.


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PSoC5 Grbl with Native USB

I added native USB support to my PS0C5 port of Grbl. The PSoC has USB capability on the chip. It also has a component for using it as a USB UART (CDC Interface). This means it looks like a serial port to the connected PC and uses the standard CDC interface driver that most OS have.

I am currently only using this on the PSoC5 development board so I am comfortable using their VID and PID values. If I make some custom hardware and distribute it, I will need to get my own.


  • Low Cost – You don’t need to buy a separate USB/TTL chip
  • Faster – It should be able to run a lot faster. You can select any baud rate you want. It never converts to TTL I think the rate is meaningless. I am not sure if it translates to actual fast jobs, but it might on data heavy laser type jobs where the laser power level is changing a lot.
  • Compatibility – It still looks like a UART to senders, so you can use all existing senders.
  • Future Features – It might be possible to have the USB look like multiple features like a memory device, to make file transfers possible.

The Code

I put it in a separate repo from my last code. I started with a more recent version of Grbl, plus I removed the LCD code. I typically don’t use the LCD and prefer a serial/bluetooth remote. It could be easily added back in from the original port.

To do list?

  1. The USB is checked for incoming data in the protocol_main_loop(). Is there a way to do this with an interrupt?
  2. Arduinos have a DTR triggered reboot. Some senders expect this. Can we emulate this behavior?
  3. I want to add SD card support to Grbl
    • Then try to make that accessible as a USB drive.


If you want to help, just let me know via comments below or on the GitHub page.


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NickelBot Updates

The NickelBot has been running great, but there were a few features I also wanted to add. I made a rev 2 PCB to address them.

Laser Door Interlock

There is a door switch that cuts power to the laser. I did this by splicing into the 12V power line going to the laser. I thought that was an effective, but ugly hack. There is now a dedicated connector for that switch.

Fan Control

On rev 1, the fans run continuously. This reduces my run time, when I run off a battery. I added a FET to control the fan power. I want the fans to turn on whenever the laser fires and stay on for a few seconds after the last pulse. Since the controller is a PSoC, I was able to implement this as a custom hardware peripheral. I used my pulse extender component.

Here is the schematic. The trigger is connected to the PWM signal going to the laser (labeled spindle). There is a 16 hz clock that is used to count down a short delay after the last pulse.


Using a connected computer sort of spoils the coolness of these tiny machines. Using a phone and BlueTooth is way cooler.

Most of my other tiny CNC machines use BlueTooth. I don’t know why I forgot it this time. It is the first time using an HC-05/HC-06 bluetooth adapter with PSoC, so that might be the reason. I decided to use a second UART, so I could use both USB/Serial and Bluetooth at the same time.  The changes to firmware where pretty trivial.

Grbl Controller Shout Out

The main Android phone app I use is Grbl Controller. It really works great and is so easy to use. It works great with the cheap HC-05/HC-06 BlueTooth adapters. I just send gcode files to my phone and run them from there. I can even turn the phone “off” and stream from my pocket.

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NickelBot – Complete

The NickelBot is complete and it works great. The goal of the project was to create an easily portable machine that creates low cost items that could be given away at events like Maker Faires. I think it has completely achieved that goal. The nickels are purchased from Amazon and cost about $0.08 each.

Here is a video that explains the machine.


It is quite reliable and the cycle time is is just about right at 1-2 minutes per nickel. I think the engraving quality is quite good. I ran it at the Chicago Northside Maker Faire last weekend. It made about 60 nickels without any problems. Here are some of the nickels it made.


The NickelBot uses (2) NEMA14 stepper motors in a T-Bot configuration. These drive a single GT2 6mm belt. The linear bearings are (2) 6mm rods per axis with (1) LM6LUU per rod.

To handle the nickel loading and unloading, it uses a single micro hobby servo. This servo  connects via a 0.03″ brass wire to a clamp. The firmware has (3) positions hard coded for the servo for fully open, nickel support only and supported plus clamped.

All 3D printed parts are PLA printed on a Lulzbot TAZ6. The colors just represent the color that happened to be in the printer at the time.

The Laser Module

The laser module is a 3.5W peak, 450nm (blue) laser. It comes with a laser power supply that has a 12V power input and TTL laser control input. It also comes with a 12V 5A power supply. I bought it a few months ago from when it was on sale for about $70, but they are typically around $99.  I control the engraving power with a 5kHZ PWM from the microcontroller.


I used a PSoC5 development board as a plug in on a custom PCB.  I knew adding an additional, accurate PWM for the servo was going to be vastly easier on the PSoC5 vs. an Arduino.

This dev board has a built in programmer debugger that makes firmware development very easy. It is great to be able to set breakpoints and check values with the debugger. I have have a another blog post with more details on this here.


The firmware is a modified version of my PSoC5 Grbl port. The only modification needed was the code to handle the clamp servo. Rather than adding special gcodes for the clamp, I simply re-coded the M7,M8 and M9 coolant commands. I did this because all of the parsing and protocol issues were already done.  Each command represents one of the clamp positions.

I may post the source code on Github soon.


The machine has (2) home switches (X and Y). A homing sequence needs to be run each time you power up the machine.  All other locations are referenced to this location. A one time  calibration is done to locate the following locations.

  • G54: G54 is the the default work offset. I decided to use the center of the nickel as the 0,0. I jogged the machine visually until the nickel looked centered. I then set the G54 location with this gcode line”G20 L10 P0 X0 Y0″. I made a target shaped graphic that I used to test engrave this location(see above). I used a caliper to measure the centering error, jogged that amount and reset the 0,0. I did this about 5 times until I was satisfied with the centering.
  • G28: I used the G28 location as the location under the nickel hopper. You jog to the location and set it with “G28.1”.
  • G30: I used the G30 location as the position over the eject chute. This is set with the G30.1 gcode command.


I am using LaserGRBL.

This is a great program for this application. It does everything, starting with a bitmap image, to gcode sending in one application. It also has some macro (multi-line gcode) buttons that are very handy. The only drawback for some is that it is Windows only.

Here is an example of the macro to get the nickel.

G90G0X0Y0 ; rapid move to absolute 0,0
M9 ; loosen clamp
G28 ; move under nickels
G4 P0.75 ; wait for nickel to fall and settle
M7 ; close clamp
G4 P0.5; wait a bit
G0X0Y0 ; return to 0,0

Source Files

Possible Improvements

  • Interlock switch: Right now there is no interlock switch for the door. If I make a new PCB, I will add a provision for that. I’ll probably just break all power to the laser module.
  • Nickel Flip: Right now the nickel always comes out of the chute upside down. This is not the best presentation. This was a compromise to make the machine as small as possible. The nickel has to fall between the Y rods. Rather than makethe distance between the rods wider than the nickel, I designed and aligned the clamp/support system so that one side of the nickel falls first and goes between the rods closer to vertical.  There is a probably a way to design the chute to catch the nickel before flips over completely or re-flips it back.
  • Software:
    • More automation: LaserGRBL has macro buttons for the nickel feed and eject features, but it would be nice if that was automatic. They have added a gcode header and footer feature to the roadmap. Right now you can generate the gcode, save the file and paste the nickel handling code in an editor. That file is then fully automatic.
    • Customizing: It would have been fun to easily add names, etc to nickels for people.

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NickelBot – Laser Controller

Here are some details on the custom laser controller I made for the NickelBot, wooden nickel engraving machine.

I want to use Grbl to control the machine. Grbl has support for lasers that allows better power control during the engrave. It also has the Core XY support I need for the H-bot mechanism it uses. The only feature I needed that it did not have is a hobby servo output.

A hobby servo requires a PWM signal. Normal Grbl runs on a ATMega328p cpu (Arduino UNO). The 328p has 3 timers that can be used to generate PWM signals. Grbl uses all 3 of them. You can attach more than PWM output to a timer, but the only timers that would work are only 8 bit timers. That is not going to give me the resolution I want.

A hobby servo uses a 1ms to 2ms pulse that repeats every 20ms. This means you are only using 1/20th of the duty cycle range. 1/20th of an 8bit signal is pretty rough. I could have used an Arduino Mega to get some more free timers, but I did not want to deal with the physical the size of a Mega.

My solution was to use a PSoC5. I have already ported Grbl to it and it has plenty of high resolution PWM components. I used the following PWM configuration…

  • 16-Bit resolution
  • 1 MHz Timer
  • 20000 for the period (=20ms)
  • 1000 to 2000 and my compare value range (1ms to 2ms)

This gives me a resolution of 1000 or 0.18° (exceeds servo’s capability)

Here is an image of the raw PCB.

Here are the features of the PCB

  • Has a socket for a CY8CKIT-059 PSoC5 development board (only $10-$15). The only drawback is the wiggly printed USB connector.
  • 1A 5V power supply for servo
  • (2) Sockets for Pololu footprint stepper drivers.
  • (2) 12V fan connectors
  • Servo connector
  • Homing switch connector
  • Laser connector (power and PWM)
  • (2) general purpose I/O for buttons, etc
  • Extra 5V power access connector.

Source Files.


The board is fully tested and 100% functional. I have it hooked up the the machine and have tested the following.

  • Home switches
  • CoreXY motor control
  • Servo control
  • Laser PWM.
  • Fans

Suggested Changes

  • The control signal on the laser supply appears to turn on the laser if left open. Therefore if the controller is not powered or actively driving the pin low, the laser will fire. That is not good. I have not tested a solution, but I think a resistor of 2k-5k Ohm pulling the pin to ground will keep the beam off when not driven low. It should be quite easy to solder this resistor between the laser pulse pin and the adjacent ground pin.



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Wooden Nickel Engraver Update

I got a chance to do some work into this project and I made some progress.

The X,Y mechanism is a free standing H-Bot. Here is a bottom view. You can see the Y home switch and the bottom of the servo to control the nickel.

Here is a top view of the mechanism. The yellow clamp piece opens partially to create a platform (ledge) for the nickel. This slides under the nickel feed tube and a nickel drops in. The bed is extra wide, so there is always something supporting the nickels in the feed tube.

The servo then clamps the nickel by pushing the tang on the yellow clamp piece into the nickel. Once the engraving is complete, the clamp completely retracts, removing the ledge. The nickel falls through into a hopper that is accessible from the front. This allows for a fully automated process and you don’t need to open the machine.

Here it is with a nickel in the clamp.

I have a temporary enclosure for testing. This supports the XY mech. You can see the nickel feed tube and the laser module support bracket. Currently it is open and a little larger than necessary to make it easy to test. It will eventually be cleaned up and get an access door with a window.

The next step is to work on the firmware. I plan to use Grbl in Core XY mode. I need to add a way to control the servo and figure out some commands to  control the nickel handling.

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Building a TWANG32

ESP32 Programming

The first step is to program your ESP32. The kit I sell on Tindie requires the use of the NodeMCU-32s. It needs to match this footprint and pinout. Note: Some version of my kits include a pre-programmed ESP32.

Arduino IDE Setup

You need to compile and upload the firmware using the Arduino IDE. Get the latest version here. You need to add some additional software.

  • Install Arduino Core for ESP32. This gets the files require to program an ESP32 There are instructions here.
  • Install FastLED Library. The FastLED library is used to control the LED strip. Go to this page and download the latest version as a zip file. In the Arduino IDE select the SketchInclude LibraryAdd Zip Library. Then select the zip file you just downloaded.
  • Install RunningMedian Library: This library is used to filter (reduce noise) the accelerometer sensor using a 5 point median filter. You can get the library here.
  • Download the TWANG32 Sketch Source files. All of the files should be placed in a folder called TWANG32.


Open the TWANG32.ino sketch in the Arduino IDE you will see this near the beginning of the file…

// what type of LED Strip....uncomment only one
#define USE_APA102
//#define USE_NEOPIXEL

You need to uncomment (remove //) in front of the line for the strip type you have. In the case above the program will compile for the APA102 type strips. Make sure only one of the #define lines is uncommented.

Open the settings.h file in the same folder as TWANG32.ino. Change the #define NUM_LEDS  144 to the LED count you plan to use. This sets the default number of LEDs in your strip.

Next to the following steps to compile and upload the firmware. This could take several minutes to compile.

  • Under the ToolsBoards menu, select the NodeMCU-32S board
  • Connect the ESP32 to your computer.
  • Select the correct com port from the ToolsPort menu.
  • Click on the Upload button.

Install the ESP32 in the PCB.

The ESP32 should be installed with the USB connector aligned with the edge of the PCB. See the image below.

Print the plastic parts

The STL files are here. If you don’t have a printed, reply in the comments and I can get you some for a reasonable price.

All of the files can be printed in high speed mode. No fine details are required. They can all be printed with no support, except for the cover which has a small pocket on the bed side. I use PLA with 2 perimeters and 20% in fill. All of the screws self tap into the plastic.

Note: I made a recent change to eliminate the use of hot glue, some of the pictures are from earlier versions.

Attach the Adhesive Rubber Feet to the Chassis.

Attach the feet into the pockets on the bottom of the chassis.

Install the PCB into the chassis.

The PCB mounts directly on the bosses on the bottom of the chassis. Use flat head M3 x 12mm screw installed inserted the chassis bottom, through the PCB and into M3 x 12mm plastic spacers. Spacers are easier to use than nuts because they are easier to hold during installation.

Assemble Joystick.

Place clamp ring over door spring. It is important to do this first because it is difficult to do later. Next screw on the the lower part of the knob.

Slide the accelerometer module wires through the lower knob and spring. Push the accelerometer module into the pocket. I have recently made changes to remove the need for hot glue. This uses M3 x 10mm (button or pan head) to hold on the cap. I use a little piece of anti-static foam (in kits) to hold the MPU-6050 accelerometer module down. If you don’t have the foam use 2 dots of hot glue in the corners with the mounting holes.


Attach the cap. Align the hollow arrow side of the cap with the little notch at the top of the lower knob. This hollow arrow will show you which side points forward in a later step.

Attach the metal cap to the bottom of the spring. This cap allows the spring end to sit flat on the cover. It should be screwed on about as much as shown in the image.

Attach the joystick to the cover. Make sure the hollow arrow is pointed forward (the closer edge). Before it is fully tightened twang it a few times. This will relax  the spring so you can see if it still points forward. Do this a few times and adjust to make sure it points forward. It does not need to be perfect… +/- a few degrees is OK.

Attach the speaker using M3 x 10mm screws.  If you angle the wires a little, it makes the wiring a little easier later.


Attach the LED cable. Your LED strip should have come with a mating connector. Some types have 3 wires and some have 4. Mate it to the LED strip. See what colors do what functions by looking at the strip labels. The strips have an arrow pointing the ways go from zero up.  Most strips have connectors on both ends. Us the connector on the base of arrow side.

All LED strips should have a + and -. These could be labeled 5V and Gnd. Do not rely on the traditional red+ and black- wire coloring. The strips are often not wired that way. Attach the wires to the terminal block. I like to add a cable tie behind the wall to act as a strain relief. I also label my wires, but you need a heat shrink printer for that.

Attach the rest of the wires from the cover. Attach the speaker connector and the accelerometer wires.

Attach the cover.

At this point you should be able to power up and play.















TWANG Shield Rev. 2

I recently ran out of the original TWANG shields. I took the opportunity to make a few changes.

Audio Jack

The internal speaker is powered by the Arduino I/O pins. This limits it to the low voltage and current that those pins can provide. In normal environments that sound has plenty of volume. I have used it at some very loud events where that sound level is not loud enough.

This version adds a standard 3mm (1/8 in.) audio jack. You can connect this to a powered, external speaker.

Power Capacitor

Some old LED strips like the WS2812 are very sensitive to voltage spikes that might come from lower quality power supplies at turn on. They recommend adding a large capacitor to reduce voltage spikes.  A larger 1000uF capacitor has been added to the PCB, so you do not need to install it externally.

Life LEDs

The TWANG firmware supports the use of remaining life LEDs. The firmware normally shows the remaining life LEDs on the LED strip.  This has the advantage of making it easy to change the lives per level without having to change your hardware. On version 1, there was a place to install (3) life LEDs, but the LEDs were never installed.  This version removes that feature.

Where to Get One

They are currently for sale on Tindie.

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Next Project – Wooden Nickel Engraver

I started working on my next backpack scale CNC project. My backpack scale projects are tiny CNC machines that I can easy carry in a backpack to tech meetups and events. This machine is going to be a wooden nickel laser engraver.

Wooden nickels are small wooden discs. You can buy blanks from various places, including Amazon. You can usually get 100 for less than $10. The goal is to create a machine that loads them from a feed tube, engraves them, then ejects them.


The basic drive will be an H-Bot. It will be similar to the midTbot, but the motors are at the ends of the X axis. It will be fully enclosed, but I not started work on that part yet.

Disc Feed System

I hope to be able to use a single hobby servo to handle the loading and unloading of the blanks. The servo will control a sliding device that has three positions.

  • In the first position it acts like a support shelf for the disc. The bed slides under the feed tube and a disk drops into the pocket.
  • The next position is the clamping position. This holds the disc still while engraving.
  • The final position retracts the shelf so the disc drops through.


The goal is to use a low cost controller like an Arduino Nano.

  • (2) Stepper motors for the X,Y motion
  • (1) Hobby servo for the disc feed system (PWM)
  • (1) Laser power control (PWM)
  • (2) homing switches
  • (1) interlock switch loop if there is a door and/or cover


The major new feature of this design is the disc feed system, so I am primarily working on that right now.

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TWANG32 – An ESP32 Port of TWANG


I ported the TWANG game over to ESP32. I wanted to do this for several reasons.

  • Cost: The ESP32 is generally lower cost than the Arduino Mega
  • Speed: The ESP32 has a dual core 80MHz processor vs. the 16MHz Arduino Mega
  • Memory: The ESP32 has much more RAM and program space to allow more features, levels and audio files.
  • Physical Size: A Mega is very big. This creates a large enclosure that takes a while to print. The smaller enclosure is also more portable.
  • DAC Pins: The audio capabilities on the Mega are very crude and basically limited to square wave tones. A DAC can output digital audio. Currently I am just using a similar square wave tone to the Mega, but it works much better for adjusting the volume.
  • Wireless: The ESP32 has Wifi and Bluetooth. This will allow easier (smartphone) interfacing for options (brightness, volume) and level pack uploads. I also want to consider dual player battle type games with linked controllers.

The Audio

The original TWANG bit banged audio directly from I/O to a speaker. This was super simple, but the volume at max was not loud enough for noisy environments. The ESP32 I/O is a lower voltage (3.3v) and less current, so something needed to be done. I prototyped with a PAM8403 based amplifier (~$4 on Amazon). This worked great, so I added that I.C. to my shield. The volume is controlled by the amplitude of the DAC.

The Shield

I made a shield to simply the wiring and provide a stable way to mount the ESP32. I used a NodeMCU 32S development board for the ESP32. Under the ESP32 is a the audio circuitry. I should have some extra boards to sell on Tindie soon. I will publish the source files soon.

The Firmware

The code is on Github. The port was relatively easy, but I had to rewrite a few libraries. They were designed so the main “setup” and “loop” parts did not change much. Currently the serial port based setup from the Mega version was not ported. This probably won’t be used. A wireless version is in the works.


The new enclosure is smaller. It prints quicker and is easier to fit in my backpack. The size is still big enough to hold comfortably while playing. The files will be uploaded to Thingiverse within the week.

Next Steps

  • Wireless control: I want a simple way to read the game statistics (average score, levels played, boos kills, etc) and tweak simple settings like audio volume and brightness. I think the easiest way is to make it a wifi access point with a simple web server. This eliminates having to write any client side apps and any smartphone or computer can hope on easily.
  • Levels: Make some way to edit or upload levels via wifi.
  • Multiplayer: I should be able to link multiple controllers. If I can think of a good dual player game idea, I might try to add that.
  • Python: It might be a fun challenge to write the game in Micro Python. This might open up the development to more people.

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