Questions regarding Duet 3 when Pi is powered separately



  • Hello Everyone,
    Apologize for the length of this post but wanted to be thorough and make sure this won’t cause any issues.

    I’m interested in powering the Duet 3 and Pi from separate sources instead of powering the Pi directly from the Duet 3 and have a few concerns. As you can imagine, powering separately would result in the Pi or the Duet being in different power states (pi on with the Duet 3 off or vice versa) and would like to make sure there aren’t any known issues before proceeding with this configuration.

    Overview
    My goal is to reuse an existing system that was built to properly shutdown and power on a Marlin/Octoprint based printer. To reuse this system requires the duet and pi powered separately so the duet can be immediately powered down and the pi can be gracefully shutdown automatically by pressing one button on the printer’s enclosure.

    As Built
    There are four illuminated momentary push buttons on the printer enclosure connected to an arduino that control the state of four relays connected to mains power. When pressed, the button toggles the state of the button’s light, its corresponding mains relay and also transmits the relay state to a home automation (HA) system. One relay is connected to the 24v power supply (duet), the SSR for the heated bed and completely cuts power to the printer. Other relays control the enclosure heater and lights. This allows the HA system to know the relay state and also control the relays (and button lights). When the HA sees the printer power relay change state it then shuts down or turns on the Pi via ssh commands and controls the Pi’s Power over Ethernet (POE) port on the network switch. The HA also actively controls the enclosure temperature and lights but those are outside the scope of this post.

    This might sound complicated but it’s very easy see the state and properly power on or off the printer and Pi, enclosure heater or lights by pressing a button on the printer’s enclosure or via my HA (Tablets throughput the house or Hey Siri, turn on the printer). This is how it’s done with a different Marlin/OctoPrint based printer and I would like to do this for the Duet 3 also. Not to mention there are also several safety features implemented as the HA knows the hotend, bed and enclosure temperatures and can cut mains power if there are any problems.

    Hope this all makes sense. I can provide more info if necessary.

    Questions
    1.) If the pi or duet 3 are in different power states, will they connect when both are powered on? Or will manual intervention be required, like pressing a connect button in OctoPrint?

    2.) How will the Pi react to booting with the Duet 3 powered off? For instance will any processes hang on the pi until the duet 3 is powered on?

    3.) If the Pi and Duet 3 are both powered on and working properly, then power is cut to the Duet 3, how does the Pi react? Does it display a notification that connectivity is lost with the Duet 3?

    4.) Is there a recommended power on or off sequence? Like should the Pi be powered on last and off first?



  • @mwolter said in Questions regarding Duet 3 when Pi is powered separately:

    2.) How will the Pi react to booting with the Duet 3 powered off? For instance will any processes hang on the pi until the duet 3 is powered on?

    for now it'll just result in a http/500 error on the web server, nothing will hang to prevent the user from using the pi with x/shh.

    3.) If the Pi and Duet 3 are both powered on and working properly, then power is cut to the Duet 3, how does the Pi react? Does it display a notification that connectivity is lost with the Duet 3?

    duet web control will indicate the connection is lost.

    Not 100% sure about the other two, but believe the order doesn't matter as long as the Duet 3 is idle/not printing. Will report back tomorrow after testing if no-one else does it first.



  • @mwolter said in Questions regarding Duet 3 when Pi is powered separately:

    Questions
    1.) If the pi or duet 3 are in different power states, will they connect when both are powered on? Or will manual intervention be required, like pressing a connect button in OctoPrint?

    The Duet3 doesn't initiate communications with the pi and the DSF running on the pi is smart enough to detect when the Duet3 goes away and comes back.

    2.) How will the Pi react to booting with the Duet 3 powered off? For instance will any processes hang on the pi until the duet 3 is powered on?

    The Duet Control Server won't start BUT it keeps retying until it makes contact with the Duet3. Once it's done that once it'll detect and recover as above.

    3.) If the Pi and Duet 3 are both powered on and working properly, then power is cut to the Duet 3, how does the Pi react? Does it display a notification that connectivity is lost with the Duet 3?

    Yes. The DWC will tell you when it does away and comes back again.

    4.) Is there a recommended power on or off sequence? Like should the Pi be powered on last and off first?

    I always power the Duet3 first just so that it's available when the Duet Control Server starts but that's just personal preference.



  • Thank you @bearer and @gtj0. Sounds like it should work well. 👍