Duet expansion board (ENA) only outputs 3.6V



  • I purchased the Duet Expansion Breakout Board and wired to my Duet2Wifi.
    https://duet3d.dozuki.com/Wiki/Duet_Expansion_Breakout_Board

    All motor controls and direction works. Enable/disable motor does not respond.

    I am unable to get my external driver to enable or disable the motor winding. My external driver manual says I need 5V to disable and 0V to enable.

    When I measure the ENA+ and ENA- pins on the breakout board, I read 3.6V disabled, and -3.6V disabled. How come the voltage is not 5V and 0V? How come there is a negative voltage instead of a 0V too?

    I also measure the DIR+ and DIR- pins and they also ready 3.6V and -3.6V.
    My driver can register direction change, but why not enable?

    What would I need to do to get 5V signals?

    Here is the driver manual:
    https://www.orientalmotor.com/products/pdfs/opmanuals/HM-60128-8E.pdf

    _
    With this information, I assume STEP+ and STEP- will also be at 3.6V. My manual says it needs 5V. When operating at 5V will this pose a possible problem in the long run? Does using 3.6V means that the step ramp time will be longer because of the lower voltage activating the transistor?


  • administrators

    The differential outputs help the LEDs in the optocouplers in most drivers turn off faster. Also they are compatible with drivers that accept RS485 signal levels instead of 5V. Most external drivers are quite happy with the 3.6V differential signals. However, for those few drivers that really do need 5V, you can achieve this by connecting STEP+ from your driver to +5V (available on the two Servo connectors), and STEP- for your driver to STEP- on the expansion board. Similarly for DIR and ENA.

    However, I think the particular issue you are having is the ENA input on your driver is a Disable input, not an Enable input. You can fix this by swapping the ENA+ and ENA- wires.



  • @dc42 said in Duet expansion board (ENA) only outputs 3.6V:

    The differential outputs help the LEDs in the optocouplers min most drivers turn off faster. Also they are compatible with drivers that accept RS485 signal levels instead of 5V. Most external drivers are quite happy with the 3.6V differential signals. However, for those few drivers that really do need 5V, you can achieve this by connecting STEP+ from your driver to +5V (available on the two Servo connectors), and STEP- for your driver to STEP- on the expansion board. Similarly for DIR and ENA.

    However, I think the particular issue you are having is the ENA input on your driver is a Disable input, not an Enable input. You can fix this by swapping the ENA+ and ENA- wires.

    Thank you so much for the explanation!
    I just checked with my oscilloscope and found that the edges are very clean and the driver likes it.

    I tried reversing the ENA logic through software and also wiring without any luck.

    What worked in the end for me was I connected everything as normal and then tapped GND to ENA+
    I measured the current draw and it was 0.20ma. This current draw seems very low and looks fine now.



  • Thank you so much for the expl
    What worked in the end for me was I connected everything as normal and then tapped GND to ENA+

    Hi, currently designing similar project (Nema23 on Duet). Just a few questions please.

    What do you mean "connected everything as normal"? Did you remove the breakout board and connected just in the expansion header?

    Also what do you mean by "tapped GND to ENA+"?

    Thanks in advanced.


  • administrators

    Duet WiFi or Ethernet will drive Nema 23 motors directly if you choose the motors carefully. Duet 3 will drive Nema 23 motors easily, and we use it to drive Nema 34 motors too.



  • Hi Mr. David Crocker 😊, thanks for the reply, can you please recommend a Nema23 and/or external driver specs that will work well with the Duet 2 Wi-Fi please? I saw Thom's Interview in TCT2019 regarding Duet3, it's a beast! Up-to 6.3A if I'm not mistaken, is it available now?


  • administrators

    Duet 3 is available to pre-order now with delivery expected late November. There is a thread about this. For Duet 2 I suggest this one https://www.omc-stepperonline.com/nema-23-stepper-motor/nema-23-bipolare-1-8deg-1-26nm-178-4oz-in-2-8a-2-5v-57x57x56mm-4-fili.html.



  • Many thanks! 🙂


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