Hello, I am looking to run LinuxCNC on a pi4 with 4gb, and use software step gen with a USB to DB25 cable to a cheap BOB. It's for a very simple Taig lathe. I'll control the spindle through RS485 to the VFD through yet another USB cable. Am I asking for trouble?
Using a USB to parallel port adapter will not work, like it does not work for I86 based linuxcnc. The usb protocol does not provide a real-time connection to the individual DB25 I/O pins. It works for printers because you write a complete 7-bit character in one go, and printers buffer the input before they process it, making it much less dependent on timing.
With the RPi, you take the signals from the 40 pin connector on the board, provide optical isolation and adapt the I/O signals to what you need to drive steppers / servos and read home and limit signals. The electronics is not complicated, but requires some design and soldering work if you make it a DIY project. You could this way wire up the parallel port of a BOB, but you need in any case 3.3 to 5V signal adaption.
Linuxcnc on the RPi4 is very experimental, I have a test setup that does not work yet. This forum publishes some information on how to configure the RPi, but I have not yet seen a complete example (ie with both the required .ini and .hal files) published here to copy as a test.
Third is a relatively new project. Remora.
This uses the spi output from the pi to drive a supported 3d printer main board in Realtime via SPI.
You can read about it here.
remora-docs.readthedocs.io/en/latest/
Thanks all, I ordered a Mesa 7i96 for use with my pi. If all else fails I suppose I can use a spare desktop that needs a video card. Still waiting for parts before a test can be done.
