I've provided a complete rundown of the article with code in the links section. I'll go over how to use it here.

On the TTGO wire ground to ground in your circuit Wire SDA to 21 Wire SCL to 22

Or for serial wire 17 to a serial UART TX line.

The screen is designed to sleep after a brief period in case the TTGO is on battery. Press the left button to wake it up. It will also wake on data.

Any time there's changed or incoming data, whether it's serial or I2C, it will be displayed.

Holding the left button pauses any current display, which is useful to prevent serial from scrolling by too quickly.

Clicking the right button changes serial mode from text to binary.

Long pressing the right button selects the baud rate.

Note that the limited screen size and tiny UART buffers can easily be overwhelmed by rapidly incoming serial data. In this case, serial frames will be dropped, so you'll lose parts of the output. This is a simple probe, so I didn't shoot for perfection. It's not PuTTY.