Upgrade your analog power knob

Upgrade your analog power knob

This is a upgrade of the analog power potentiometer to give you better control over the power level. It´s also easier to remember a number than a location of the pot.

You can buy this from me prebuilt, ready to connect to your machine here.
Or follow this guide to make your own!
If you want to convert your digital K40 to analog with this solution – check out this conversion article.

Tools you need

– Soldering iron and solder
– Wire stripper and cutter

Parts needed

– 10K, 10-turn potentiometer: Aliexpress | Ebay
– 3-wire voltmeter, 0-30 or 0-99 volts. Aliexpress | Ebay
– Knob for the potentiometer, 6mm shaft. Make sure to check specs. on the potentiometer you buy.
– Heat shrink and some cables, 0.5-1mm2 is good enough.

Connect it

Here is a overview of the connections you have to make.
I did this in a cartoon-ish style, so everyone can understand how it all connects.

There is two approaches to this upgrade.

1: Re-use the cables already on the old pot.
2: New cables from the power supply.

Depending on what you choose, you can splice the cables on the old ones or add new cables all together.
Depending on how your panel looks the length of the wires can vary, look at the schematic above to see how to connect everything and choose the length you need on your machine.

Step-by-step list

I have written a easier step-by-step guide here to solder it all up.
This approach replaces all three cables from the power supply to the pot.

Step 1: Measure how long cables you need from your PSU to the panel, remember to account for the lid opening. As a example: 300mm, cut and strip the ends on three cables.

Step 2: Measure distance between the pot and the voltmeter display, where you want to place it. Let´s say 100mm, cut and strip the ends on three cables.

Step 3: The volt-meter has cables already soldered on it. Solder the 100mm and 300mm cables to them, making a Y-connection. Remember to add the shrink tube over the soldered connection, or insulate it with electric tape.

Step 4: Solder the 100mm ends to the potentiometer, as shown on the picture above.

Step 5: Replace the old cables on the power supply with the new 300mm cables you just made.
Replace the potentiometer in the panel and make a hole for the voltmeter, or just let it sit on top of the panel 😉
If you have the newer style PSU with white connectors for 5V,GND and IN, splice the cable on the old connector. Or buy JST 2.5 XH connectors from Aliexpress or Ebay to make it look a bit nicer.

Thats all for now, power up the machine and check out your now improved power control 🙂

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Comments (7)

  • Brian Reply

    Thank you.

    17 January, 2018 at 19:08
  • Alex Reply


    Thanks for the great guides your site is the best resource for information on the k40 🙂

    I have one question, this replaces the already existing potentiometer right? Can you set the laser power while the laser is not firing with this mod?

    6 June, 2018 at 12:01
    • HP Persson Reply

      Thanks! You can set the power when you want, while firing or idle, it doesn´t matter. I use to tweak my cutting with the power knob while cutting to get the best result.

      6 June, 2018 at 13:19
  • Alex Reply

    Thanks for the answer! And I’m supposed I’m right by doing the following?

    Replace poti which is in k40 now with the new one and just wire the voltmeter into the circuit and I should be fine?

    6 June, 2018 at 19:42
    • HP Persson Reply

      Yes, just make sure you grab a 3 wire meter and put the sense wire on IN wire to the PSU, if not it will die because the volts goes down lower than it needs to light up 🙂

      6 June, 2018 at 19:58
  • Roland Reply

    Thanks for the post. Just wondering if I can keep both the amp meter and have the 3 wire volt meter on the same pot?

    Thanks you.

    6 August, 2018 at 21:53
    • HP Persson Reply

      Yes, and its recommendet to keep the mA-meter too, as the volt-meter only give you reference for cutting or engraving power, not maximum as the mA-meter can give you details about.

      6 August, 2018 at 23:06

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