Your guide to installing Smoothieboard in a Blue Box Laser Cutting machine

( See also http://smoothieware.org/blue-box-guide )

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« Blue Box » laser cutters ( sometimes also refereed to as K40 ) are cheap chinese machines basically designed for laser engraving of stamps.

The electronics and software that come with it are generally considered barely usable, and are at the very least very limited.

However, the machine itself, while cutting cost at all corners, and not being of the best quality, is a good option ( and the cheapest option possible ) for anybody looking at getting started with laser cutting.

These machines can be found for $700 or even sometimes less on ebay, and have become more and more popular as people have started replacing the internal electronics, first with Arduino-based boards, and now with Smoothieboard. This allows for easier use, more software options, and makes for an overall much better machine.

Their work area is roughly A4 size, and the laser power is about 40W.
This allows the machine to cut and engrave plywood, MDF, balsa, cardboard, paper, leather, cloth and PMMA ( acrylic ), up to about 5mm thickness.

This is a step-by-step guide to connecting your board to the various components of the laser cutter, configuring everything, from the beginning to actually cutting material.

This guide is a community effort, and this page is a Wiki. Please don't hesitate to edit it to fix mistakes and add information, any help is very welcome.

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About this guide

This guide is specific to the « Blue box » model that is very commonly found, but the information it contains should be useful for most chinese laser cutters.

Larger chinese models have higher quality, and function on basically the same principle ( except they use external stepper motor drivers ).

There is a more general guide : the Laser Cutter Guide. You should read it before you read this guide, as it contains much information you need to be familiar with to do things properly.

This guide is based on Stephane BUISSON's blue box build log.

Safety

Lasers will make you blind. In an instant. In the blink of an eye, quite literally.

Never look into the beam or at any surface the beam might reflect off of

Never have the machine powered while the door is open.

You are responsible for your own safety.

Eyes can not be replaced.

If the machine does not come with a switch on the door that turns the laser off when the door is open. This is stupid and dangerous. Please install that switch.

If you leave your machine alone even for a few minutes, this can happen to you :

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Warnings

Before you start wiring your machine's elements to the board, there are several things you need to keep in mind and be careful about during all of the assembly.

Make sure you read this. Seriously.

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Polarity

Always make sure the polarity is correct when wiring in power inputs (coming from the Power Supply). Reversed polarity can damage or destroy all or part of your board. Polarity is indicated on the board itself by the + and - signs. Double check. On older versions of the board, markings are partially hidden by the connector, making it confusing. Rely on only the diagrams.

To check the polarity of your power source, attach your multimeter probes to the two wires of your power source respectively. If the voltmeter reading is positive it implies that the red probe is connected to the positive wire (+) and the black probe to the negative wire (-).

The main (labeled VBB) power input has a reverse polarity protection, however, it will not hold forever. As soon as you notice something is wrong, turn the power supply off and check again.

Disconnecting

Never disconnect or connect stepper motors from the stepper motor drivers while the board is powered (i.e., when the Power Supply is turned on).

The drivers have very good protection against most possible problems and are very hard to destroy accidentally. But it is possible.

Shorts

Be careful that nothing metallic ever touches the board while it is powered on. Falling screwdrivers, nuts and bolts can cause shorts and destroy the board.
Check the board before powering it on.
Do not press the reset button with anything metallic, as you could slip and cause a short, use a plastic screwdriver or the like.

Use the right connector

Always check the schematic before connecting power sources (coming from the Power Supply) to the board. Connected to the wrong connector can destroy components. A common example of this problem is plugging a power input cable, into the connector for an output, or plugging the limit switches in backwards.

Crimping

Make absolutely sure of your connections using crimps or screw terminals, from wires to any type of connector, are very careful and well done. Connections (to the stepper motors for example) lost while the machine is running can destroy your board.

Markings

In the case of the VBB power input, be careful. If your board came with connectors pre-soldered, the 5mm connector is present, and the polarity of that connector is that of the large traces in the wiring diagram to the right (red is +, blue is -). On some boards, the marking on the boards may be hidden by the connector itself, so for VBB, do not rely on the markings on the board, but on the diagrams on this page. However, if you did not get your connectors soldered, and want to solder a 3.5mm connector instead of a 5mm connector, also note that the polarity is the opposite.

USB v Ethernet

USB can, in some setups, be subject to interference, which causes disconnections, and can ruin your work. This is very hard to prevent if it happens even in normal conditions. Ethernet, on the other hand, does not have this problem: save yourself the trouble, and use Ethernet right away. It's very nice. See Network for information on how to set it up.

Destroying your board

If you receive a bad board, you will get a replacement. But if you destroy your own board, your only options will be to fix it yourself (which can be quite difficult), or get a new one.

This is why it is very important you make sure you do not destroy your own board. Smoothieboard is reasonably protected, but there are still things that will destroy it. The general idea is: if a part of the board gets too much power, it will get destroyed. Here are some common mistake users do that cause the board to get too much power and die: 

  • Plugging 12-24v (motor power) into anything you are not supposed to. Like the 5V line, or an end-stop or thermistor input for example. Problems with the 5V or 3.3V power are not as much of a problem as the board is 5V-tolerant, so wrong connections and shorts should be okay as long as they do not last too long.
  • Shorting 12-24v to anything else, which is essentially the same as plugging it into a place you are not supposed to (see above). This can happen by dropping a metal object onto the board, bad soldering, loose wires, un-protected wires, etc …
  • Using an inductive load (like a motor, fan or solenoid) on a MOSFET, without a diode across (see Fan documentation).

The general idea here is: always make sure everything is clean, and double-check everything before turning the power on. You can not learn by making mistakes here, as mistakes will likely cost you your board.

Electrostatic discharge can also destroy your board : make sure you properly ground everything.

Heater safety

If your machine contains any heating element and uses the temperature control module to control it, please make sure you read the section about implementing all safety measures here, and implement as many as you can. Fires will kill you if you don't.

Grounding

Make sure your machine's case and electronics are properly grounded, also make sure your location's electrical installation's grounding is correctly done. See for example :

For a good read about safety, you can refer to the RepRap Wiki documentation on the subject

Inside the machine

If you look into your machine, you will see two main electronics items :

The power supply

The laser Power Supply ( PSU ) converts the mains ( 110 or 220V AC ) power into very high voltage ( several thousand volts ) that is fed to the laser CO2 tube.

In the case of these small blue box laser cutters, this PSU also provides 5V power for the electronics' logic, and 24V for the stepper motors.

The exact model may vary depending on your exact machine's model, manufacturer and version. Here in this tutorial we will be using the MYJG40W from http://www.jnmydy.com, but other PSUs should be very similar in their wiring and function.

If your PSU is too different from the one in this guide to allow you to adapt the instructions, please contact the community.

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Here are the various connections you will find on your PSU :

Connector Connection label Name Description
High power L- Mains Ground Connects to the mains ground wire and to the enclosure for grounding
FG Laser Ground The ground side of the tube connects to this connection
AC Mains Alternative current from the mains cable
AC Mains Alternative current from the mains cable
Logic G Logic Ground Common ground for all logic signals
P or WP Safety switch The laser won't fire unless this is connected to Ground, used for the door switch
L or TL Fire switch The laser will file if this is connected to Ground, used for the test switch
G Logic Ground Common ground for all logic signals
IN Input Reads an Analog or PWM signal to set the laser's power
5V Logic power 5V to power the controller board's logic
Low power +24V Motor power 24V to move the stepper motors
G Power Ground Common ground
5V Logic power Unconnected
L ? Unconnected

The controller board

The controller board connects via USB to your computer, receives data ( like an image to engrave ), and controls both the stepper motors and the laser power, to obtain the desired result ( an engraved image ).

The controller board that comes with the blue box is very limited, and can only interface with the crappy closed software that comes with it. This is essentially why you are reading this guide : the goal is to throw this board out, and replace it with a Smoothieboard.

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Basic power

First things first, you need to provide power to your Smoothieboard.

There is a 4-pin 5mm connector on your Smoothieboard with a VBB/GND and 5V labels.

You will want to connect 24V power to the VBB input on the Smoothieboard, 5V power to the 5V input on the Smoothieboard, and ground to GND :

Connector Connection label Name Description
5V Logic power Connect to the 5V power input on Smoothieboard
+24V Motor power Connect to the VBB power input on Smoothieboard
G Power Ground Connect to the Ground input on the Smoothieboard
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Once this is wired, if you power the laser PSU, the Smoothieboard should turn on, and both the red VBB LED, and the orange 3.3V LED should light up.

Controlling the stepper motors

Your machine has two stepper motors, one for the X axis, and one for the Y axis. Each motor has 4 wires, controlling two internal coils.

If you are using a Smoothieboard in a blue box, you will want to wire each of those stepper motors to one of the stepper motor drivers on the Smoothieboard ( M1 for X, and M2 for Y ).

If you are following this guide along but are using a larger machine than the blue box, then it's very likely your machine came with external stepper motor drivers, and you want to simply have Smoothieboard control those via their step/direction/enable interface. If this is the case, please look at the laser cutter guide's section on external stepper motor drivers.

The first thing you want to do, is find the wires for each stepper motor, and follow them to the controller board.

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Once you have located each set of 4 wires, separate them from the rest, and for each, make a 4-pin connector using the connectors and crimps that came with the Smoothieboard.

Note : The stepper motor wires come on ribbon cables, and are arranged in a specific order. You need to keep that order when connecting them to the Smoothieboard, you can not connect them in a random order. If you lost the order, look at the laser cutter guide, it has detailed information on how to figure this out.

Then connect the X stepper motor to the M1 stepper motor driver, and the Y stepper motor to the M2 stepper motor driver.

Finally, in your configuration file, change alpha_current and beta_current to the value 1 ( for 1 Ampere ), and change the alpha_steps_per_mm and beta_steps_per_mm to the value 157.575.

Once this is done, connect to the board via USB using software such as Pronterface or the web interface, power up the machine, and you should be able to move the stepper motors, and therefore the axes, using the controls in the software.