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Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
@stozk
Ok I think I figured out the problem.
Most likely the Cruis module, as well as the Adafruit module have pull-up resistors built in (the Adafruit has them).
And the "cheap" heltec module doesn't. So adding 4,7k Ohm resistors to the i2c pins will fire up the display.