Installation instructions MG


You’ll be disconnecting connectors from your K40’s existing controller, and reconnecting them to the Mini Gerbil.  It’s a great idea to read all the instructions below before starting.  Basic familiarity with connectors/electronics is helpful, but the forum is a great place to ask questions if you’re unsure about anything.  Typically takes 10-20 minutes.

There are two K40 versions (plus sub versions e.g. Digital Control vs Analogue):

  • ribbon cable version (X axis motor plus the limit switches)
  • non-ribbon version – individually wired x/y axis and limit switches (more info is provided in the forum, see click to thread on k40 forum page)

There are two types of limit switches (or end stops):

  • mechanical limit switches which has just two leads: signal and ground
  • electronic limit switches which has three leads: signal, ground and 5 Volt to power it

There are two types of PSU’s (Power Supplies):

  • All crew Terminals
  • Micro plugs for LP(2pins),WP(2pins),PWM(3pins)

There are two types of limit switches (or end stops):

  • mechanical limit switches which has just two leads: signal and ground
  • electronic limit switches which has three leads: signal, ground and 5 Volt to power it

Assemble you Mini Gerbil case first if you have a Mini Gerbil Case. Click here for a new Page.

Tools and materials:

  • Small screw driver
  • Small nose pliers


1.  Turn your K40 power off at the wall (powerpoint).


2.  Open up the main panel on the right hand side of your K40.  Inside you’ll see an electronics enclosure which is the K40 power supply:

PSU Type I
PSU Type I
PSU Type II (Lid or Test button)

The leftmost connector in the above diagram is the mains voltage power connector – no need to touch this.  The Gerbil installation only uses the leads associated with the centre and rightmost connectors.

3.  Follow the the wires from the front of the power supply to the circuit board on the back of the K40’s front panel, and you’ve found the K40’s old controller, which looks like this:

(photo courtesy of :

4  Temporarily attach a label to any similarly coloured wires on the old controller so you can identify them later on if necessary

5.  Take a close up photo of the wires coming into the old controller (like the above photo), ensuring you can clearly see which wires and labels attach to the various connectors.

6.  Now take a look at the Mini Gerbil.  It has headers (plastic tabs) with a lock mechanism to help you avoid plugging connectors in the wrong way around.

Even though the Mini Gerbil has an Acrylic case, it’s good practice to keep it secure, so mount it fixed in front of the K40 power supply.

Disconnecting the old controller and connecting the Mini Gerbil

7.  Unplug the small 4 wire Y axis motor connector from the old controller and plug into the Mini Gerbil headers, as shown in the picture below.  The header lock mechanism prevents incorrect orientation. Note: if the machine does “home” away from zero during testing then you need to turn the connector 90 degrees or configure the firmware to revert the Y direction (via command $30=0)

Mini Gerbil board

8.  Unplug the large 4 wire Low Voltage connector from the old controller, and plug into the large header on the Mini Gerbil labelled J3 ‘Lo/5V/Gnd/24V’.  The header lock mechanism prevents incorrect orientation.

Labels on Mini Gerbil

The photo above shows labels on the Mini Gerbil to aid orientation of the large low voltage power connector.  (In some older versions of the K40, the connector has 6 positions with 4 wires. You can extract carefully the metal connector inserts and re-seat them in the right positions/sequence in the 6 pin socket connector and slide the 6 pin connector over  the 4 male pins. Alternatively you can buy a standard 4 pin (MTA-156 – 4 Position 3.96 mm pitch) PC connector and use this to connect the Gerbil controller to the Laser power supply. See Digikey MTA connectors)

9.  Unplug the ribbon cable from the old controller, and plug into the long thin slot in the Mini Gerbil.  The metal lips of the ribbon cable must face the edge of the Gerbil, as shown below. If your version has not a ribbon cable then read about it in this it describes it in details with many photo’s.

10.  Confirm your Y axis, Low Voltage and Ribbon (or alternative no ribbon) connectors are now plugged into the Gerbil like this:

K40 installation with a ribbon cable containing x motor and xy limits
K40 with a ribbon cable installation diagram
K40 installation without a ribbon cable
K40 without a ribbon cable with mechanical end switches
Electronic limit switches wiring
Electronic limit switches wiring diagram
Location of the non-ribbon limit connector
Limits connector on the Mini Gerbil, note Y,X,Gnd positions. On some K40s the mating catch is on the other side, just insert the connector with the catch facing away from the tab on the Mini Gerbil header. The 5V is used on electronic limit switches.

The The middle of the current control (potentiometer or digital control panel) needs to be disconnected from the terminal strip and be replaced with the provided single wire with the Female/Male Dupont connectors. The wire connects the Mini Gerbil pwm (pulse width modulation) output to the current control input of the power supply as depicted above (labelled ‘IN’ terminal). The old current control wire can be left disconnected or connected by a three way switch (see wiring diagram) so you can select between Mini Gerbil pwm control or Digital/manual Pot control of the laser current via the existing control.

Photo of a test set up

Note: If you still want to use the test push button then you need to include a three way switch so the IN has a reference voltage when firing the test switch. This can be handy for mirror alignment. When doing mirror alignment you need to set the Mini Gerbil in CNC mode ($32=0) to allow the laser to fire while not in motion. Don’t forget to switch back to Laser mode ($32=1) ! Alternatively you can define a macro ‘test fire’ button in LightBurn.

Alternative wiring of test switches:

Air assist option: If you have a 24v pcb fan as air assist

The mini pcb fan has a positive red lead and a negative black lead that you need to extend with the supplied extension cord. The extension cord needs to be fed through the drag chain (included in the Pro pack). Use the stripped lead in the extension cord as the negative ground. You wire this up to the 24V and ground screw terminals on the laser psu. This is the most right connector/terminal that has 4 screw terminals. The first (starting from left) is the 24 volts output followed by ground and LO (Laser On) terminals. (see

This page will be updated with a link on how to connect the optional Door-Pause-Resume-Abort connections.

11.  Disconnect the existing K40 USB lead from the old controller and plug into the Mini Gerbil.  Plug the other end into your PC/MAC as usual.

Questions ?  Please check our forum and refer to the instruction numbers above if posting a question

12. Test the basics of the controller via your G-code sender or Lightburn (console or arrows)

  • Unlock the machine: $X
  • Home the machine:$H
  • Move axis: G0 x10 Y10

Troubleshoot it if necessary via the troubleshooting chart here

Finished. Great, now you’re ready to go onto Using the Mini Gerbil with Inkscape see Using Gerbil

(LightBurn/LaserWeb instructions see here)


you can use any G-code sender to manually test the conversion:

Mirror Alignment

Go to Mirror Alignment page:

For all commands see Configuring Mini Gerbil wiki