CO2 Laser power supplies and Duet

  • I did find out today that the new laser mode is available in the 2.02 beta.

    Now I am asking myself how to best use it with a CO2 power supply.

    Those supplies have two inputs, one PWM or analog imput that defines laser power (called IN) and two Pins (TL and TH, one active low, one active high) to turn the laser on/off.

    What I do at the moment (I am still using smoothieware for my laser, but I am not too happy with it's performance) is that I put the IN pin to +5V (enabling full power) and then use the pwm signal from smoothie on the TH pin to contol output power.

    This works well but the power supply is making quite some high pitch noises because (I guess) the Laser is switched on/off at the very high pwm frequency.

    Perhaps a better way to operate the power supply would be to have the PWM signal on all the time and to turn on/off the laser with a second pin.

    The function of the pin would be to switch state on every begin/end of a G1/G2/G3 , the PWM signal would go to IN and the switch pin would go to TL or TH, which ever is better for making sure that the laser does not fire on boot.

    Is this something that is doable/makes sense? Did anybody already try this?


  • administrators

    If the IN pin allows you to control the laser power right down to zero, then I suggest you feed the Duet PWM output pin (the one you specified in the M452 command) into that pin. You could use a separate GPIO pin to do on/off switching at the start and end of a job too if you like.

    Alternatively, if the cutting speed is slow you could wires it as you have done for Smoothie but reduce the PWM frequency.

    Please note, RepRapFirmware does not yet adjust the PWM during acceleration and deceleration the way Smoothieware does. I plan to implement that before the 2.02 release. However, I'd like to get some feedback on the current implementation first, so that I know it is basically doing the right thing before I make any changes.

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