Non PWM Led



  • I'm using duet wifi to build pick and place machine with bottom vision camera and led ring around it.

    I have problem with horizontal lines on camera image and I suspect it might be caused by Led controlled by PWM from Fan2 output.

    Is there any way to switch off PWM on fan and just have plain voltage control instead?

    Thanks
    Arkadiusz



  • why dont you just get the 24V or 5V from the Powersupply or a respective pin? see Duet pinout

    https://duet3d.dozuki.com/Wiki/Duet_Wiring_Diagrams

    and the answer is yes of course. What you could do aswell is increase the pwm frequency



  • @Arkadiusz said in Non PWM Led:

    Is there any way to switch off PWM on fan and just have plain voltage control instead?

    using 0 and 100% should not flicker unless you have a LED driver after the Duet, if you need to dim the leds without using PWM then no, not without basically buying or building a high end LED driver.



  • @taconite I cannot have this LED always on, I need to be able to switch in on and off with m106 commands.



  • @bearer I tried all sorts of PWM values, I don't really need to dim them but I have to be able to turn it on and off with G-code commands. And I don't have any driver after duet, just a resistor



  • Using S0 and S1 is all on or all off, as should S0 and S255 (how it differentiates beween S1 and S1 i do not know..)

    you're using https://duet3d.dozuki.com/Wiki/Gcode#Section_M42_Switch_I_O_pin ?



  • Yes S1 and S0 works for me but Led it too bright I needed to dim it.

    Anyways got this issue solved, I added step down DC converter between Duet and Led, now flickering is gone.



  • Huh, would have thought dc/dc is switch mode and would also flicker, otherwise I'd suggest that. Probably got lucky with the switching frequency, but if it works, why is less important:D


  • administrators

    The flickering was probably caused by the supply voltage varying as the bed heater is PWM'd.

    To use a DC-DC converted with the LED (or a fan), connect the input of the converter to VIN (or an always-on fan output to get the benefit of fuse protection), and connect the LED between the positive output of the converter and the FAN- or HEAT_ pin of your chosen heater or fan output. Never connect the input of a DC-DC converter to a heater or fan output.



  • I guess I got lucky, 1st rule of engineering: If it ain't broke, don't fix it 🙂



  • @dc42 Never connect the input of a DC-DC converter to a heater or fan output. - I did exactly that, what might be consequences?

    I will follow your advice, thanks for letting me know.


  • administrators

    @Arkadiusz said in Non PWM Led:

    @dc42 Never connect the input of a DC-DC converter to a heater or fan output. - I did exactly that, what might be consequences?

    I will follow your advice, thanks for letting me know.

    It's likely to blow the mosfet that controls the heater or fan output, because of the surge current to charge the input capacitor of the buck regulator every time it turns on. A heater output might last a while, but a fan output is likely to fail quite quickly.


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