[solved] : Issue with standard ATX_PSU and PS_ON pin

  • Hi all,

    I migrated last night my printer from the 0.8.5 to the Duet Wifi. A challenge to get all the new connectors crimped and after fixing some loose/broken crimps
    my printer runs now on the Duet Wifi.
    Had to adjust config and macro files but this seems to be ok now.

    My issue it the PS_ON function with ATX PSU.

    This all was working on hte 0.8.5 but witht th Wifi the PS_ON signal is not staying at GND level.

    I use a push button to connect the ATX PSU PS_ON pin to GND, after I have done this, I can normaly release the push button and the Duet keeps the PS_ON pin on GND.
    I used a second push button to short reset to GND from the expansion header to switch the PSU off (Web buttons works also) That was working on the 0.8.5

    On the Wifi, the board starts as long as I press the push button to short PS_ON to GND, as soon as I release it, the PSU stops working.
    I habe a normal swith in parallel to the push button to keep the PS_ON pin permanently on GND level and can use the Wifi.

    My question is, what need to be done to have the PS_ON pin from the Wifi working (means keeping the signal to GND level as long as the reset or ATX Off is used ?
    Is there a difference between the 0.8.5 and the Wifi ?

    additonal infos :
    I did not made and firmware updates yet, still running on 1.15b as delivered.
    I tried the 5v jumper on both settings, internal and external 5V, no changes
    The 5Vin pin uses normal 5V from the ATX PSU not a standby 5V (I do not want to have the Wifi always powered just to allow remote starting) this worked on the 0.8.5
    Power messure :
    Duet Wifi on !!!
    5v ATX PSU -> GND = 5.12 V
    5v ATX PSU -> PS_ON pin = 5.12 V
    5v ATX PSU ->5V in pin = 0,24 V

    Duet Wifi off !!!
    5v ATX PSU -> GND = 0 V
    5v ATX PSU -> PS_ON pin = -4,91 V and GND -> PS_ON pin = 4.91 V
    ( this means the Duet Wifi stores ~ 5V+ which means ATX PSU goes off, as long as no shortage to GND forces PS_ON to GND level ? )
    5v ATX PSU ->5V in pin = 0,24 V

    update 1
    I use now the +5V VSB standby power and still see the same behavior.
    I have run a different test. I connect nothing to the 3 pin conenctor for external 5V power and mearured the PS_ON pin against +5 V.
    Duet Wifi powered off :
    PS_ON pin shows no potential against + 5V

    Duet Wifi powered on :
    PS_ON pin shows 0 V against +5V
    Here I would expect 5 V on the multimeter when powered on the PS_ON pin is going to GND, so it looks like something is not working as expected with the PS_ON pin.
    Is there any jumper or firmware config that may be responsible for the PS_ON pin not going to GND level ?
    I put the jumper for 5V to the internal position and still the same (unexpected) behavior

    (I have made a test messarurement +5V against GND from the allways on fan and the multimeter shows (as expected) +5 V)


  • Is anyone using the PS_ON functionality with the Duet Wifi and can provide some details how he has wired it ?

    I have currently no clue what might be wrong here.

  • administrators

    In case it's a firmware issue, please make the connection between PS_ON and your PSU again, send M80 and then measure the voltage on the PS_ON pin. It it still shows 5V then I think your Duet is faulty.

  • Hi David,

    thanks for the advice.

    PS_ON signal seems to be working, but a bit different than from the 0.8.5.

    I connected the PS_ON , +5 V BSB and GND to the external 5 V connector and the Duet Wifi is powered.
    I can use the M80 to power the PSU and M81 to power off, I can do the same with the ATX buttons from the Duet web frontend.
    Power ATX on and off.

    But I can not controll the PS_ON signal with just a short triggering of the PS_ON to GND like on the 0.8.5.
    Looks like the default behavior on the Duet Wifi is PS_ON off and on the 0.8.5 was PS_ON on.

    Is there a different way (pin) that I can use to have a normal power on hardware button ?

  • administrators

    I'll check the firmware. Have you tried putting a M80 command at the start of config.g?

  • I just tried it.
    I have put the command M80 into the first line of the config.g file.

    This works as expected, when pressing the push button for > 3 seconds. Looks like the Duet Wifi needs some seconds for booting
    up and reading the config.g file.
    May be some change of the hardware design is responsible for the different default behavior of the board during powering on.

    Anyhow it works now as expected, many thanks for your fast support David.
    One thing I need to mention. If the M80 command is inserted into the config.g file and +5V VSB ( standby) power is conencted, you can not switch off the board by
    doing a reset, as after reset the config.g is read and the board powered complete on again. So this is only a solution in a case like mine, powering on via push button.


  • administrators

    I have just checked the code, and the firmware starts up with the ATX power pin not active (and has done for many versions). So what I don't understand is how it worked for you on the Duet 0.8.5, if you didn't have a M80 command in config.g before.

  • I'd like to point out that there's an easier way to try to use the PS_ON pin: supply the Duet with an always-on 5V. Then the Duet can freely switch the ATX supply on or off as needed without affecting its own ability to execute commands or respond to WiFi. ATX supplies provide such an always-on 5V supply, so people using an ATX supply can easily do this.

    It sounds like you're trying to do something trickier: allow the Duet to turn itself off completely. For that you have to keep the power on until the Duet can command it to stay on, as you have discovered.

  • administrators

    I think that a long time ago, I may have had the firmware start up with ATX power enabled, but I changed it to disabled because of user requests. Perhaps that was to avoid power getting turned on when you apply USB power.

  • administrators

    It certainly makes more sense to not turn ATX power on until commanded to do so.

    I have extended the Power Supply section of the documentation a bit in light of this thread:


  • One short update here, may be a info that could go into the wiki also.

    I use the switched +5 V power ot the ATX PSU to power the Duet and for switching on the duet I need to
    keep the PS_ON lead from the ATX PSU grounded manually for ~3 seconds, after the blue LED near the wifi module
    flashes a bit brighter and goes off.
    Than the duet PS_ON pin goes to GND and I can release my mechanical push button.

    Note : I decided to go this way, because I do not want all the electronics to consume power without any purpose.
    I have (currently) no plan/need to switch the printer on remotely without being there to watch the print start.

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