This page details the hardware installation side of Setting Up the Gerbil

Video with instructions

Photo: Plugging large connectors into the Gerbil


You’ll be disconnecting connectors from your K40’s existing controller, and reconnecting them to the 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.


Tools and materials:

  • small square of cardboard, around 10cm x 10cm



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:

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 Gerbil… beautiful, isn’t it ?  It has headers with a lock mechanism to help you avoid plugging connectors in the wrong way around.

Even though the Gerbil has 4 rubber feet, it’s good practice to keep it away from the K40 metal frame, so lay it on the small square of cardboard down in front of the K40 power supply.


Disconnecting the old controller and connecting the Gerbil

7  Unplug the small 4 wire Y axis motor connector from the old controller and plug into the 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)

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

The photo above shows labels on the Gerbil shield 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 Gerbil.  The metal lips of the ribbon cable must face the edge of the Gerbil, as shown below.

10  Confirm your Y axis, Low Voltage and Ribbon connectors are now plugged into the Gerbil like this:

The middle of the current control needs to be disconnected from the terminal strip and be replaced with the provided single wire. The wire connects the gerbil pwm 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 so you can select gerbil pwm control or manual control of the laser current via the existing control (stock k40 current control potmeter or digital control unit).

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 followed by ground.

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

11  Disconnect the existing K40 USB lead from the old controller and plug into the 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

Great, now you’re ready to go onto Using Gerbil;


you can use any G-code sender to manually test the conversion: moving x and y axis, homing direction and laser function. CNCjs is a good g-code sender  (Click here to goto cncjs dowload page) but any other will do too. The default behavior of Gerbil when powered up is the alarm status (motor axis Lockup as per cnc standard). You need to clear the controller alarm via a command “$X”. The Inkscape plugins do that clear command by default when streaming the g-code files. After issuing a “$X” you can issue a g-code command like “G0 X1 Y1” t’o move the gantry or issue a “$H” to home the machine to its zero coordinates (Left Top corner same a stock K40). Command “S100” turns the laser on where the number stands for the power e.g. 100 equals 1mA.


G1 X1 Y1 S100 F800


stands for: M4 laser on, Goto coordinates X,Y (1,1) at 800mm/min with the tool (laser beam) pwered at 1mA and switch it off (M5). G0 is a move without any tools enabled.