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 (30)

  • Brian Reply

    Thank you.

    2018-01-17 at 19:08
    • Giavonni Reply

      Im having a problem. Wired like the diagram showes. Problem is my mA meter at full power is only registering 4mA but I know it really more than that. With the old pot it showes full power at 20mA. It the same pot,3590s-2-10 as you show with the wiper in the center.

      2019-03-07 at 00:20
  • 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?

    2018-06-06 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.

      2018-06-06 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?

    2018-06-06 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 🙂

      2018-06-06 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.

    2018-08-06 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.

      2018-08-06 at 23:06
  • Ken Knutson Reply

    So if I understand correctly, The POT wiper wire and the middle wire (mine is yellow) on the digital meter go to the “IN” on the Power source. The red wire on digital meter goes to the 5v power and the black goes to Ground power.

    Thanks for you post!!!

    2018-08-29 at 01:51
    • HP Persson Reply

      It depends on the POT, check the markings on it. Some have the wiper on the edge away from the knob, others in the middle. You will notice it quick, if the voltage doesnt move, or going the wrong direction you have another type of pot. But you can google “potentiometer wiper” to see what the symbol looks like.

      2018-08-29 at 09:02
  • dave Reply

    can that Pot just be used as a replacement? Rather than adding voltmeter?

    2018-11-06 at 13:08
    • HP Persson Reply


      2018-11-07 at 07:24
  • Matt Reply

    Do you have a link to the conversion from digital to analog you mentioned in the article?

    2018-11-09 at 19:39
    • HP Persson Reply

      Ah, it got lost when i remade the website. I´ll see if i find it in a backup again.

      2018-11-10 at 14:50
  • Matt Reply

    I tried to instal a 10 turn Pot and i have two issues. First It appears to turn the wrong way, turning counter clockwise increases the mA. Second. I don’t seem to have any resolution between 0mA and about 15mA. Can you help?

    2019-01-16 at 00:50
    • HP Persson Reply

      Change the position of 5V and GND cables, and it moves correct again. It probably solves the problem you have with no power in the lower end.

      2019-01-16 at 07:15
  • Bo Reply

    I haven’t yet received my K40, but I have a question about the PSU.

    On my 100W laser, I can adjust the maximum output of the psu so I don’t ever go over the rating for the tube – is that not possible with the K40 power supply – is everything controlled by the pot on the control panel?

    So… incautious use of the dial can overdrive the tube, easily?

    2019-04-25 at 06:10
    • HP Persson Reply

      Yes, a MA meter on the k40 is a must, and keeping it below 16-18mA

      2019-04-25 at 06:15
  • B Reply

    Great artical. would have a diagram for the newer power supply.
    I want to get rid of my digital unit. add ammeter, also install pot for control and a test fire button.
    spent hours tralling the net and getting confused.
    your write up seems very straight forward.
    Greatly appreciate any help.
    thanks in advance.
    p.s my power supply has the green connectors.

    2019-05-05 at 19:32
    • HP Persson Reply

      There is a article coming on this. You can find a picture here explaining what goes where -> https://k40laser.se/wp-content/uploads/2019/05/oldpsulayout.png

      2019-05-06 at 09:06
      • Flibblebot Reply

        So, judging by that picture, the connections for the green connector PSU are:
        Pins 5 & 6 -> Laser enable switch (already connected)
        Pins 7 & 8 -> Laser test button
        Pin 8 -> Pot top and volt meter black wire
        Pin 9 -> Pot bottom and volt meter white/grey wire
        Pin 10 -> Pot middle and volt meter red wire

        Is that right?

        2019-05-11 at 17:49
        • HP Persson Reply

          Yes, but, if its top, botttom or middle on the pot varies between manufacturer on the potentiometers. Positive and negative is the 5V and GND, the viper/output goes to the IN pin (9)

          2019-05-16 at 13:50
  • marc Reply

    why do you use a 10k potentiometer? In my K40 is a 1k and in other post I read that they replace with 5k.
    What size is the right one? Thanks.

    2019-05-12 at 19:09
    • HP Persson Reply

      K40´s has been delivered with different pots through the times. 1k, 5k or 10k doesn´t matter.

      2019-05-12 at 19:18
      • marc Reply

        Thanks for your fast answer 🙂

        2019-05-12 at 19:25
  • Roger Reply

    You mentioned to use a 0-30 or 0-99 volt 3-wire voltmeter. What would be the difference? Is one preferred over the other? Thanks for all the info you provide. It is invaluable.

    2019-06-03 at 14:04
    • HP Persson Reply

      No difference, the voltage from the PSU is between 0 and 5 volts, where 5 volts is max power, 0 volts no power. Most meters are 0-30 or 0.99 – which one you use is the one you can find locally, or order online. A 10v meter would work too!

      2019-06-03 at 19:34
      • Roger Reply

        Thanks. I am trying to wire mine up today. First attempt decreases the mA as I turn right. Swapped 5V and ground as you suggested above and it does increase as I turn right but something is still not right. First, the mA go from 0 to about 1,8 instantly and never go any higher. It also seems to react differently whether I have the laser armed or not. Have you seen this behavior before? Thanks.

        2019-06-16 at 02:11
        • HP Persson Reply

          Test the output of the PSU to begin with, you want 5V on the 5V line, and not anything else, no less than 4.5V. If this value is different with or without the laser enabled, there is something strange with the wiring in the machine.

          2019-06-18 at 01:54
          • Roger

            5V was good from the PSU. However, while I had the multimeter out I tested the pot and it was bad. Replaced the pot and all is well. Thanks again for all the help.

            2019-06-19 at 15:22

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