Duet 3 6HC and Pi 4 Power Question



  • Hey I've got a question about running the Duet 3 with a Pi 4. Actually more of a concern

    Say I have it all hooked up according to the instructions for using the Duet 3 with a SBC, and I need to do some form of emergency stop.

    Say it's one of those situations where it has to be an immediate stop, no time to try and access DWC or even worse it's not responding.

    The only choice is to cut the power.

    My concern is that of corrupting the SD card in the Pi and having to reload everything. I'd rather leave it powered on and just kill the power to the Duet.

    I know they can be powered separately, I'm just wondering if anyone is actually doing it and considered this situation.

    My thought was to have my regular 24v power supply wired up to the Duet. This could be run through a switch either on the AC or DC side so I could cut the power. Of course he jumpers set correctly so that no power goes between the Duet and PI

    I could then wire a a separate 5v power supply for the Pi before the switch so it stays on even if the switch is hit to kill the Duet

    Problem is the GPIO pins are occupied by the ribbon cable. Kinda only leaves the USB-C connector which means either using something that already has that connection or hacking something together.

    I thought about using a wall wart style power supply that already has the USB-C connection, but I'd rather not have another cable running to my electrical outlet. I was thinking of either soldering wires to the AC terminals on it and running it to the spade connectors on my inlet. I also thought about using ring tongue connectors and bolting them to the holes in the AC terminals. Of course the whole thing would be enclosed.

    Or I could try using a 5v power supply like from Mean Well and figure out how to hack together a connection between it and the USB-C of the Pi.

    Suggestions?



  • you also still have the barrel power connector on the Pi



  • I don't have the pi with me but I don't believe there's a barrel connector, isn't that a headphone jack?



  • @Dougal1957 said in Duet 3 6HC and Pi 4 Power Question:

    you also still have the barrel power connector on the Pi

    Not sure if the Pi ever had a DC 'barrel' style conector, but version 3 and 4 does not.

    @blt3dp on mine I've just used 5(or 6?) single wires between the Pi and the Duet for the SPI signals and common ground, then with the rest of the GPIO freed I can run power and GPIO for a relay to control the AC supply to the machine. I.e. you don't need all the wires in the ribbon cable, just the ones mentioned here https://duet3d.dozuki.com/Wiki/Duet_3_Mainboard_6HC_Wiring_Diagram



  • @blt3dp said in Duet 3 6HC and Pi 4 Power Question:

    isn't that a headphone jack?

    true story.


  • administrators

    How about using a button to short the Reset pins on the Duet together, instead of cutting the power?



  • While I doubt it would happen with your awesome firmware, if the firmware was to hang, would shorting the reset pins still do the job?

    @dc42 said in Duet 3 6HC and Pi 4 Power Question:

    How about using a button to short the Reset pins on the Duet together, instead of cutting the power?


  • administrators

    @blt3dp said in Duet 3 6HC and Pi 4 Power Question:

    While I doubt it would happen with your awesome firmware, if the firmware was to hang, would shorting the reset pins still do the job?

    Yes, it's a direct hardware reset to the microcontroller.



  • @blt3dp said in Duet 3 6HC and Pi 4 Power Question:

    My concern is that of corrupting the SD card in the Pi and having to reload everything.

    I have maybe 5 to 7 Pi in various pieces of equipment. I have not done a clean shutdown on any of them in the last couple of years. Just yanked power. Nary a corruption. Also, most of them are not on UPS. Same story.

    It is impossible to prove a negative, and I may lose a card someday. But at the moment, I have my Pi powered from the Duet 6HC, and I have one "Mains" or "AC" power switch for the 24V supply, and I always just switch off.

    Your preference certainly may vary... me personally, I prefer to back up /sys every so often, and if I ever corrupt a card, I will rebuild it from scratch and the backup of the /sys directory.



  • @blt3dp said in Duet 3 6HC and Pi 4 Power Question:

    Say I have it all hooked up according to the instructions for using the Duet 3 with a SBC, and I need to do some form of emergency stop.
    ...
    The only choice is to cut the power.

    My concern is that of corrupting the SD card in the Pi and having to reload everything. I'd rather leave it powered on and just kill the power to the Duet.

    Suggestions?

    My planned Duet 3 setup is to separate the two. The Pi will be always-on (for networking stability, instant-on appearance, and some background safety checks). There will be a button on the machine that the PI reads that will control power to the Duet 3. That way you're just cycling power to the Duet and the motors and everything don't stay on all the time. Should also work for a reset.

    My only concern at this point is the Duet Server on the PI - I think it's counting on the Duet being 'alive' when it boots, and I'm not sure a timer check has been setup to keep trying. I'll find this one down the road a bit.



  • I am only one voice; furthermore, I wish to be respectful of others thoughts and methods.

    At the same time:

    Man, you guys really know how to complicate something simple... 🙂



  • Yeah, I’ve not had the best luck with the Raspberry Pi that I’ve had in the past. Maybe it was a cheap SD card, but I’ve always had corruption. I definitely want to separate the power for the 2. I’ve decided to go with a 5v Mean Well Power supply and wire it up separately. Then I kind of have all the options. I could do a separate reset to the Duet reset pins as well as wire up the 24v power supply to a switch so I could go either way. I did wonder about DSF though.



  • @dc42 said in Duet 3 6HC and Pi 4 Power Question:

    @blt3dp said in Duet 3 6HC and Pi 4 Power Question:

    While I doubt it would happen with your awesome firmware, if the firmware was to hang, would shorting the reset pins still do the job?

    Yes, it's a direct hardware reset to the microcontroller.

    DING! DING! DING! Reset pins for the win! My latching emergency stop button is tied directly to the reset header on the Duet3. As long as those pins are shorted, the MCU will do absolutely nothing.

    IMG_20191130_152942.jpg



  • @TLAS said in Duet 3 6HC and Pi 4 Power Question:

    My only concern at this point is the Duet Server on the PI - I think it's counting on the Duet being 'alive' when it boots, and I'm not sure a timer check has been setup to keep trying. I'll find this one down the road a bit.

    Both the Duet3 and the DSF on the pi are tolerant of the other not being there. The Duet3 could care less since it doesn't initiate anything and the DuetControlServer on the pi will keep trying to contact the Duet3 forever.



  • @bearer said in Duet 3 6HC and Pi 4 Power Question:

    @Dougal1957 said in Duet 3 6HC and Pi 4 Power Question:

    you also still have the barrel power connector on the Pi

    Not sure if the Pi ever had a DC 'barrel' style conector, but version 3 and 4 does not.

    @blt3dp on mine I've just used 5(or 6?) single wires between the Pi and the Duet for the SPI signals and common ground, then with the rest of the GPIO freed I can run power and GPIO for a relay to control the AC supply to the machine. I.e. you don't need all the wires in the ribbon cable, just the ones mentioned here https://duet3d.dozuki.com/Wiki/Duet_3_Mainboard_6HC_Wiring_Diagram

    Yeah, I use a custom cable as well and power the Duet3 from the SBC with a relay in between. It's actually controlled by a GPIO pin on the SBC so I can power cycle the Duet3 remotely should the need arise.


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