On 3/29/2018 9:46 AM, Andrew Voelkel wrote: > >> Yes, BBB with Machinekit is standard fare. There are images you can put on >> an SD. >> Charles has made the pru_generic driver, and that basically means that >> step generation is done on the PRU. >> >> If you use the BBB, you’d have to make sure you get proper isolation from >> the BBB pins to whatever you use down the line. It’s easy to fry a BBB. So >> only a PRU does not do the job. It’s the electronics coming after. > > I've been having trouble understanding this "isolation" issue, but your > email may have given me a clue. The PRU lines are just internal board > lines, not offboard I/O lines? Maybe even a level shifting problem? In any > case an extra board changes the landscape. More below ...
All of the BBB digital I/O pins are only 3.3V and have fairly low drive (typically 3 mA, it varies per pin). If any of the signals *EVER* exceed 3.3V (which is easy to do with EMI in a large machine) the CPU on the BBB will be destroyed. How much buffering and isolation you need depends on your specific machine and environment, but it's generally worth while to use a few inexpensive 74' series buffer ICs to protect the BBB and get additional drive (eg: 5V @ 25 mA for a 74ACT244 which costs about $0.25). >> Am I correct that you want to run the 7i92 from the BBB? Although I >> personally have no experience with this setup. >> >> You have to take into account that the BBB is not great when it comes to >> graphics, Axis is known to have problems when you have a lot of small >> segments. So if you want to have proper screens you could use a proper PC >> (which IMO are not very expensive). >> > > People keep mentioning graphics on the BBB, but I am also having trouble > understanding why that is a concern. I do the CAM on my main workstation (a > Mac) and preview the machine paths there. So I really don't do any graphics > in the machine control program. The BBB does not have (usable) 3D graphics acceleration, so the preview window of the default Axis display is very sluggish on a BBB, especially for complex parts (like 3D printed models). If you're OK with not having the preview window displayed, the BBB graphics work fine for the rest of the UI. > Understanding my perspective requires knowing what I'm doing now. I've got > an old laptop PC running Windows 10 and Mach3 with a Ethernet SmoothStepper > hooked up to my Gecko. I'm attracted to Linux because of the bloat and > constant updating in Windows. But at the end of the day I'm wanting to > build parts. In order to turf Mach3 I've got two choices, LinuxCNC (or > MachineKit) and UCCNC. > > If I have to run an external PC and create an extra board to buffer the > PRU, then why am I using a BBB at all? Why not just run a Mesa 7i92 instead > for stepper control? And if I'm doing that, why am I using MachineKit > instead of generic LinuxCNC with a real time kernel which supports > ethernet? You wouldn't need an external PC. If the graphics on the BBB are not to your liking, you can use a remote interface (typically an Android tablet). Or you can switch from the BBB to a PC which has good graphics and use Mesa hardware for the hard real-time signals. > And if running ethernet is a road less travelled even with generic > LinuxCNC, then I have to ask myself why I'm not just buying a UCCNC > ethernet card for about a hundred bucks and using the UCCNC software which > is 55 euros, and just tolerating Windows. One thing about that setup is > that I know it will be up and working quickly. There are lots of people using Ethernet with LCNC/Machinekit, including the latest machines from Tormach (which currently use a 7i92 with a custom FPGA configuration). > It's frustrating because I like the idea of non-bloated Linux and an > "embedded PC" which is part of the router and packaged that way, but I'm > beginning to think it isn't worth the effort. > > Given my perspective, do you have any advice? If your machine needs Mesa hardware, I'd recommend using a standard PC with either LCNC or Machinekit (of course we'd recommend Machinekit here, but that choice is a whole different discussion!). If you can get by with the BBB's limited graphics (or a remote UI on a tablet) and buffering a few signals, the BBB is an inexpensive and "non-bloated" solution. -- Charles Steinkuehler char...@steinkuehler.net -- website: http://www.machinekit.io blog: http://blog.machinekit.io github: https://github.com/machinekit --- You received this message because you are subscribed to the Google Groups "Machinekit" group. To unsubscribe from this group and stop receiving emails from it, send an email to machinekit+unsubscr...@googlegroups.com. Visit this group at https://groups.google.com/group/machinekit. For more options, visit https://groups.google.com/d/optout.
