Need Help! GRBL: EN pin on the Pololu A4988 driver board is staying high.

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Thread: GRBL: EN pin on the Pololu A4988 driver board is staying high.

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    Default GRBL: EN pin on the Pololu A4988 driver board is staying high.

    I built a new pcb mill and am trying to setup Arduino/GRBL witb bCNC to run it. I found that bCNC seems to be working fine, but I am getting nothing out of the motors. I checked the enable pin on the Pololu a4988 driver board and I'm getting 4.55v between EN and the logic ground. I believe that would disable the driver. I checked the step pin on the scope and can see that it is receiving pulses. I changed the $4 setting to 1 reset the board, and got the same 4.55 volts.

    I've also checked the motors and they work fine on another project.

    Two questions:
    Am I right in assuming that 4.55v on the EN pin of the driver board would disable the motors?
    How do I bring it low when using the Arduino/GRBL/bCNC setup?

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    Default Re: GRBL: EN pin on the Pololu A4988 driver board is staying high.

    $4 = 0 should be the correct setting. Check your $1 setting and at least for testing set $1=255. This will keep the drives enabled all the time. Also, the A4988 requires a separate logic voltage in addition to the power supply for the motors. VDD and GND are the pins on the A4988 that need about 5V for logic power. This can come from the same power supply running the arduino, but it needs to be there.



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    Default Re: GRBL: EN pin on the Pololu A4988 driver board is staying high.

    ]$4 = 0 should be the correct setting.


    I will change it back

    Check your $1 setting and at least for testing set $1=255.
    I will try that


    Also, the A4988 requires a separate logic voltage in addition to the power supply for the motors. VDD and GND are the pins on the A4988 that need about 5V for logic power. This can come from the same power supply running the arduino, but it needs to be there.
    I understand that the a4988 needs two power sources....logic and motor. It appears that the drivers are pulling their logic power from the 5v pin on the Arduino. Are you saying that is not good enough. The way the board is configured, I don't know how I could supply the GRBL with another source of power other than from the Arduino. (the power to the Arduino is coming from the USB connection on the laptop) When I check the power to the EN pin, I've done it both with the motor power attached and without, and the results are the same, so I have to assume the GRBL is getting it's logic power from the Arduino ok and that the two power sources are independent of each other. Is that ok?



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    Default Re: GRBL: EN pin on the Pololu A4988 driver board is staying high.

    You can pull the logic power for the driver from the arduino if the load isn't too high. Without looking I think it will work, but you still need dedicated wiring to the A4988 VDD and GND pins. The gnd pin from the A4988 can be connected to the gnd pin on the arduino, and the VDD pin on the A4988 can be connected to the 5V pin on the arduino. I would try it with just one driver to see if it works. If it does, then I would look at running 5V from a separate power source to the arduin and the drivers.



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    Default Re: GRBL: EN pin on the Pololu A4988 driver board is staying high.

    I do not know of any way to do that without modifying the GRBL board. Even if I did manage to find a way to feed logic power, I still have the issue of a HIGH enable pin. Unless I can get that low somehow, I am not sure anything will work. The other thing about this is that the GRBL shield on the Arduino is being used by a lot of people out there and I know they are running it off the the 5v pin on the Arduino because thats the way the board is made.

    VMOT has it's own power source.

    I am convinced that there is something about the way I am setup that is causing that pin to go high. I've been searching the forums for a similar problem and so far I haven't found one. That tells me that the board is designed the way it should be at least when it comes to this issue.

    Here is the setup I am using. I set the $1 and $4 back to their original settings since changes did not help.

    $0=10 (step pulse, usec)
    $1=25 (step idle delay, msec)
    $2=0 (step port invert mask:00000000)
    $3=0 (dir port invert mask:00000000)
    $4=0 (step enable invert, bool)
    $5=0 (limit pins invert, bool)
    $6=0 (probe pin invert, bool)
    $10=3 (status report mask:00000011)
    $11=0.010 (junction deviation, mm)
    $12=0.002 (arc tolerance, mm)
    $13=0 (report inches, bool)
    $20=0 (soft limits, bool)
    $21=0 (hard limits, bool)
    $22=0 (homing cycle, bool)
    $23=0 (homing dir invert mask:00000000)
    $24=25.000 (homing feed, mm/min)
    $25=500.000 (homing seek, mm/min)
    $26=250 (homing debounce, msec)
    $27=1.000 (homing pull-off, mm)
    $100=250.000 (x, step/mm)
    $101=250.000 (y, step/mm)
    $102=250.000 (z, step/mm)
    $110=500.000 (x max rate, mm/min)
    $111=500.000 (y max rate, mm/min)
    $112=500.000 (z max rate, mm/min)
    $120=10.000 (x accel, mm/sec^2)
    $121=10.000 (y accel, mm/sec^2)
    $122=10.000 (z accel, mm/sec^2)
    $130=200.000 (x max travel, mm)
    $131=200.000 (y max travel, mm)
    $132=200.000 (z max travel, mm)
    ok

    There a lot of things I will need to change once I get past this EN problem, but for now, that's what I've got and it's not working



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    Default Re: GRBL: EN pin on the Pololu A4988 driver board is staying high.

    In that case, I would completely remove the shield from the arduino and test digital pin #8. With $1=255 and $4=0 the pin should read 0V. The $1 setting is how many msec the driver stays enabled after a step command. So the default setting of 25 means that if no step signal is received for 25 msec, the driver will disable and pin 8 will go high. Setting $1=255 tells it to leave the driver enabled all the time, so pin 8 should stay low always. If pin 8 is low with $1=255 and $4=0 then the problem lies in the board. If pin 8 is high then I would start by re-flashing the arduino and testing again. If the problem persists, then load a arduino code that cycles the pin to see if the pin on the arduino is burned out..



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    Default Re: GRBL: EN pin on the Pololu A4988 driver board is staying high.

    Ok, that I can do. Makes perfect sense to me. I will do that tonight.
    Thank you very much. I will let you know what happens.



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    Default Re: GRBL: EN pin on the Pololu A4988 driver board is staying high.

    I didn't mean for you to take me on as a hobby, but you're the only one that is talking to me about this. Thank you for your help

    Ok, here's what I did....

    1) attached GRBL shield to arduino, connected to USB on my laptop, and powered VMOT (12v). Only one driver installed and a motor connected to that driver. Measured pin 1 (EN) voltage and got 4.55v

    2) disconnected VMOT power so the shield only had 5v from arduino....still 4.55v on EN.

    3) removed the shield and measured between arduino pin 8 and GND....< 1v (LOW to my way of thinking)

    4) measured with both $1 = 25 and $1 = 255 and the voltage on pin 8 never got above 1v

    5) put the shield back on and tried it several ways (with $1=25 and 255, with and without 12v to VMOT., and always found 4.55v on EN.

    I don;'t know what goes on between the EN on the driver and the pin that connects to arduino pin 8, but they certainly are not in sync. I have to conclude that the shield is bad. I will try to find the GRBL schematic tomorrow, but that board is just to simple for there to be any kind of processing between EN and the arduino pin 8.unless there is some sort of short.

    Does this sound right to you?

    Charlie



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GRBL: EN pin on the Pololu A4988 driver board is staying high.

GRBL: EN pin on the Pololu A4988 driver board is staying high.