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3d Printer extruder issues and some other doubts

Discussion in 'General Electronics Discussion' started by Athul, Aug 4, 2016.

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  1. Athul

    Athul

    8
    0
    Aug 4, 2016
    Hi,

    First of all I don't have much experience in electronics (yes I'm anelectrical and electronics engineering graduate(fresher) but I'm more interested in power system) and I like to do hobby electronic projects with my basic knowledge in electronics. I'm having some problems with my 3d printer board, Second extruder in it turns on automatically with out any command if USB disconnected from computer and power supply is on. If I reconnect USB back to USB port(Doesn't require connection with host) it turns off.and it'll turn on again if I disconnect USB. I checked the pins which are controlling the MOSFET gate, they are HIGH without USB and and LOW with USB.

    In some boards USB s connecting to send serial data as well as powering the micro controller(for eg : Smoothieboard), so I checked the schematics and there's an inbuilt regulator and this issue has't happened to me before .So I checked the regulator output it's around 4.3 V without USB and above 4.9V with USB. So I think it's the regulator problem.

    Could there be any other reason.??
    Board = Printrboard Rev D with Extruder board
    FW= Marlin

    When I was checking the schematics of the board I noticed few things , Input to all the MOSFETs are marked with complement (Invert).

    Below is the entire schematics and part of MOSFET circut
    Printrboard_RevB_Schematic150 (1).png

    Printrboard_RevB_Schematic150 (1).png


    As you see Gate signal are marked like this
    ________ ________ ________
    PWM-FAN HOTEND HOTBED

    Is this mean they're active low???

    I know in some micro-controllers RESET pins are marked like
    ______
    RESET , that means it's active low and a LOW signal at this pin will cause reset of micro-controller. But that can't be here, since n-channel MOSFET requires a positive Gate pulse.;

    So can anyone tell me why they are marked like
    ________ ________ _______
    PWM-FAN HOTEND , HOTBED this instead of PWM-FAN , HOTEND , HOTBED

    Thanks
     
    Last edited: Aug 4, 2016
  2. Alec_t

    Alec_t

    2,883
    770
    Jul 7, 2015
    I agree. So it's presumably a programming quirk, unless the fan etc have inbuilt logic inversion..
     
  3. Athul

    Athul

    8
    0
    Aug 4, 2016

    If there was any logic inversion, shouldn't it have shown in the schematics??

    Also what do you think about automatic turn On of extruder?
     
  4. Alec_t

    Alec_t

    2,883
    770
    Jul 7, 2015
    The fan itself isn't in the schematic.
    I wouldn't have designed it that way :D.
     
  5. Athul

    Athul

    8
    0
    Aug 4, 2016

    Do you have any idea why is the extruder turning ON when USB is disconnected?

    Could this be the regulator issue??
     
  6. Alec_t

    Alec_t

    2,883
    770
    Jul 7, 2015
    The regulator has no obvious interaction with the USB section. USB disconnection would be detectable by the micro, but what the micro does in response is down to the programming.
     
  7. Athul

    Athul

    8
    0
    Aug 4, 2016

    I've using both boards for around 6 months. I never had the problem. Both etruders turn on only when command is give to turn them on , otherwise it was OFF with or without USB connection. Second extruder issue happened recenly. SO I think it's an issue with control board.
     
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