Arduino Opta Serial and I2C Breakout

The Arduino Opta micro PLC is a fairly new product by Arduino, developed in collaboration with relay manufacturer Finder. The device features four powerful relays, eight digital/analog inputs, Ethernet, and a USB-C connector for programming. To access serial (beyond USB) and I2C connections, you’ll need to do a bit of light hacking, e.g. pry off the aux tab.

On the other side of this tab is a pattern of surface-mount pads with connections for Serial1 and I2C, along with GND, 3.3V, and 5V as outlined here. To connect to these pads, I used a KYOCERA AVX 009159010061916 card edge connector, along with a custom breakout board that I designed in KiCad. The Opta Aux connector and breakout are available on Tindie if you’d like to use either of these protocols.

The PCB takes the surface mount pads and connects them to a series of through-hole pads for easy access. The video below shows it sending serial communications to an oscilloscope, receiving serial via a MIDI adapter, and controlling a generic SSD1306 128x64 pixel OLED screen via I2C. While 5V is available on the breakout, so far I’ve used 3.3V exclusively to avoid any issues with 5V tolerance.

Although this adapter setup has worked quite well during initial testing, it’s meant for experimentation, and is not hardened for use in a PLC’s traditional industrial environment. You can even see it start to pull out at around 39 seconds into the demo video when rotated. Of course, one might consider a dab of hot glue to keep things in place, though I have yet to try this method!