[solved] JTech 3.8W - laser response shifted to high PWN signal?

Hi to all,
I´m a relatively new x-carve owner and just last week upgraded my machine with the JTech 3.8w laser kit.

I (hopefully) setup everything according to the instructions and hooked up the laser driver to the Spindle(PWM) [red wire] and GND [black wire] of my x-controller (still on stock GRBL; not the JTech one). Using UGS I homed the machine used “$30=12000” and “$31=0” to set max and min rpm.

If I now enter “M03 S1200” (10% laser power) i see nothing, even though this setting was considered to be used for focussing the spot. Increasing the “M03 SXXXX” command showed that I first see a slight spot at “M03 S3200” (~25% laser power). But from there on intensity is increasing super fast “M03 S4000” (~33%) already gives a real bright spot (although not burning wood yet).

I then checked the PWN/GND output with a multimeter (20 or 200 DCV) and get the follwoing reads for:

M05 (0%) -> 0.01V
M03 S1200 (10%) ->0.77 V
M03 S6000 (50%) -> 3.65 V
M03 S12000 (100%) -> 7.2 V

So voltage seems to increase linearly, but why is it going up to 7V?? Isn’t it supposed to be 0-5V? Will this higher voltage harm my laser driver board - or can i use my laser at full power without frying my board? Is that normal?

I have to mention, that I am an absolute beginner when it comes to electronics^^

Someone some ideas what I might miss? Regarding both the shifted laser response and the 7V PWM thing.

Here are some more information & images:

  • I have no spindle controlled by the x-carve
  • everything else works just fine (x/y/z axis, limit switches, no crashes)
  • Laser is connected to the laser port on the driver board and the input signal from the x-controller is also connected correctly
  • To examine the laser spot the laser is 1.5" from the material, which is the preset focuspoint for 3.8W laser.

I recommend you change to this version of grbl firmware. It has the proper PWM frequency for the J-Tech Laser Driver. The command range for laser control is S0-S255 for the PWM 0-5v.


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Thanks for the quick and helpful replies. I will do so and change the firmware.

Does changing the frimware has the potential to change the voltage output at the pwm port?

Nevertheless I will try and see :slight_smile:

Will update how it turned out.


I believe that you have a wiring error.

Remove the power wire from the laser or place it in lock-out so that the laser cannot come on.

Disconnect the wire from D11 and run your test again measuring the voltage on D11 as you change the spindle speed.

Maximum should be approximately 5 volts.

[Edit] oops. Just noticed it’s the X controller. Instead of D11 in the comment above use PWM.

Ok, uploaded the new JTech integrated firmware and directly measured the voltage of pwm. this time i unplugged the connector from the X-controller and directly measured the pins for spindle (pwm) and gnd at the x-controller.
Again 7.1V!

Unless I somehow managed to wire stuff wrongly in the x-controller (which i figured is almost impossible when looking at the instructions again), the fault might lie within the multimeter. Its really old and if my interpretation of the display is correct the battery symbol might indicate low battery…which in turn could lead to a failure of the internal reference voltage. Aaaand that (at least thats what I read) could cause the meter to read high.

I ordered a new multimeter and tomorrow (12pm here) I will try to get a working one from a colleague.

I hope that solves my “voltage-issue” ^^
Once I got the laser tested with the new firmware and checked the voltage again, I’ll report back.

EDIT: Just tested the new firmware, looks awesome! M03 S25 (10%) still burns my plywood a bit (after a few seconds), but M03 S15-20 give a nice focussing spot.
Thanks again for the help and a big thanks to Larry and everybody involved in the development of the multimode grbl-project!

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Ok got another multimeter and get the correct responses with max 5v at 100% duty cycle.

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