So close to getting things running. I am waiting on a longer cable for the pen servo (I've tested with some Dupont connections but want something a bit better before running it in place on the hanging plotter).

I've been trying to get the computer to talk gcode to the plotter.

In the original article, Universal GCode Sender (UGS) is the recommended and documented way to get things going. The firmware code is written so that when the start button is pressed, the Pico outputs a couple of lines of information to the serial connection, identifying as a build of the GRBL firmware for CNC machines. The idea appears to be that given those two lines of information, UGS should say "OK, that's a machine running GBRL", and then you should be able to hit the "play" button to send the gcode file across.

I've spent a fair bit of time trying to follow Ben's description in the article, with the latest version of UGS on macOS, and it just will not open a clean and complete connection to the board. I've been as far as checking the debug logs from UGS; putting a build of grblHAL on another Pico and trying to get UGS to talk to that (UGS doesn't properly support grblHAL at the moment, AFAIUI); and comparing the serial output and conversation sequence between UGS and other CNC machines, based largely on blog posts and reports from GitHub issues and wiki descriptions.

It looks as though UGS sends $I followed by $$ followed by $G to check on board capabilities.

I've added a small amount of  GRBL command handling to the firmware. I have the Pico respond to these commands in a meaningful(ish) manner, but the connection never seems to fully resolve to a point where UGS will let me hit play. This is fair, because the controller is not running full GRBL, but it is a bit annoying that the recommended software cannot be persuaded to act as a simple sender and pipe gcode over serial.

(I believe the controller is doing its job, though; I've pasted in some of the gcode commands from one of the sample files at the serial prompt in the terminal, and had the servo and stepper motors start to move around, indicating that they are being driven by the commands)

Basically, either my setup is behaving differently to Ben's system from the HackSpace article; UGS has been updated since May 2022 (very likely); or, something else. There's a possibility it's an OS-specific thing, too - I'm trying this on macOS Sonoma; the article appeared to use Windows (?); I do have a Linux machine available as well, but I haven't tried on there as yet.

I've tried bCNC (a Python GUI); but for some reason that is not even wanting to find my USB serial port. As an aside, it also looks absolutely terrible / barely readable in dark mode on macOS.

I finally hit potential success with CNCjs, an Electron-based GUI, which is letting me connect... which I installed using homebrew. I did have to make a small tweak (specifically, turning off system quarantine for the app via xattr -d com.apple.quarantine /Applications/CNCjs.app) to get it to run without complaints. When I have the last piece of wiring, I should be able to try one of the test plots.

In the end though, this minimal approach may be too little, and it may be that I should switch across to a more functional (grblHAL?) firmware of some kind, assuming that I'd be able to figure out how to have that drive a hanging wall plotter...