EMI, a cautionary tale

The other day, I received an anxious message from a friend. His CNC router was randomly stopping in the middle of every job. Over 5 years ago, I helped him build his machine using one of my Teensy 4.1-based controller boards, so I was familiar with his setup. It had been running fine since then and he claimed to have not changed anything on it. I recalled that even though his board had the Ethernet kit installed, he had opted to use USB to connect. "It works, and Ethernet sounds like too much hassle," he said at the time. However, from his description of the problem, it sounded like EMI, but he wasn't so sure.

So, I went over to his shop to see what I could do. His machine setup uses an old laptop that is connected via WiFi, so it had a free Ethernet port. Expecting to switch him to Ethernet, I brought a spare cable, just in case. I had him run an "air cut" that demonstrated the problem, and within about 5 minutes, the machine stopped running. His GCode sender was non-responsive. Definitely a problem.

I suggested that before we do anything else, we set up Ethernet. Skepticism was evident, but he reluctantly agreed. Using the grblHAL Web Builder, we rebuilt the firmware to include networking (and in the process brought it up to a recent version of grblHAL). I configured grblHAL to use a static IP mode ($301) and then configured his Windows 10 machine to have a static Ethernet port. When the cable was plugged in, the activity light on the T41U5XBB Ethernet jack started flickering. I went through the "get ioSender to let me switch to Networking" dance. (Unplug the USB cable, run ioSender, change the connect dialog to networking, plug USB back in, and connect. Whew!). We were graced with a connection, and I verified that it was network-based.

Next, my friend ran the same job and it did not fail. It happily ran to completion. I stayed long enough for him to run the actual cut and it completed. My work was done and I took my leave, secure in the satisfaction that it wasn't my board at all and that demon EMI was slain. I received a message the next day that the machine had completed a 2+ hour job with no hiccups. A few days after that, he dropped by with a nice bottle of Longshadows Cabernet Sauvignon as thanks. Perhaps the best gift of all was his admission that he was wrong about Ethernet.

So, the clear message is use Ethernet and not USB. Even if it works fine with USB right now, EMI can creep in and ruin your job.