On Sunday, June 30, 2019 at 12:46:29 PM UTC-7, Charles Steinkuehler wrote: > > You should be able to hook to the DB25 directly vs. digging into the > control box, but you'll likely need some buffering. The BBB I/O pins > are only rated for 3.3V with 3-6 mA drive (depending on the pin), > which isn't really enough to directly drive an opto. >
So very much like the ESP32/Grbl-esp32 which got me started down this path. 3.3V GPIO little drive capability > > The CRAMPS board doesn't really help a lot, since it doesn't buffer > the step/dir lines (the small Pololu stepper drivers don't present > much load on the step/dir pins). > > I'd recommend one of two options: > > * Create your own DB25 cape for the BBB using a prototype cape and a > generic buffer like a 74HCT245 or something. There aren't a lot of > wires so it shouldn't be much harder than the "flying wire" adapter > you made for the Nano. :) > That might not be a bad idea and I think I have a BBB prototyping Cape somewhere. But the 4n26 opto isolators are rated at 60mA and selecting the level shifter or line driver is where I'm stuck right now. I have some TXS108E bi-directional level shifters with 50ma drive capabilities but was told the pull-up instead of drive-up could be problematic. https://www.ti.com/lit/ds/symlink/txs0108e.pdf I might have some 74HCT245's here so can test the ~20mA drive capability with respect to the opto-isolators. And I might build a more generic board onto an DB25P so I can swap in/out the Nano, ESP32 and BBB. It might take those imported CNC machines through 3 levels of capabilities with BBB/Machinekit the ultimate. > > * Create a small Pololu sized buffer board that drives the step/dir > signals onto the 4-pin stepper motor header. This would let you use > the CRAMPS board (or any other board that used the Pololu style > drivers). I've thought this would be a good open-source project, and > would be useful for *anything* that uses the Pololu style drives (not > just BBB based capes) and would allow safely driving larger stepper > motor drivers. > I wish there were 5V on that driver pinout.. I suppose there could be a jump on the Vcc pin to bring in something other than 3.3V. With only 3 lines a small quad channel shifter would do the trick. Still need to find what the 4N26 requires to turn on though. Interesting. Thanks for the feedback and ideas. -- 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. To view this discussion on the web visit https://groups.google.com/d/msgid/machinekit/bdab013d-c797-4673-94d8-9f46c9ddd76a%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
