I often revise my code several times also have several NodeMCU boards with different programs installed. I finally figured out how to blink the on board LED with the version of code installed on that board.
Using millis and % (remainder operator) the on board LED will now blink ‘version blinks’ pause ‘code update blinks’. So 1 fast and 4 long blinks in approximately 500 ms at a 50% duty cycle.
Simple changes will change the duty cycle and blink duration. I used 4800 ms with 2400 half cycle because 2400 is easily divisible by 1, 2, 3, 4, 6, 8, 12.
For version 0-1 the numbers would be: %2400<2400 (no fast blinks) and %2400<1200 (1 blink on for 1.2 ms).
Use unsigned long variables as shown to minimize millis rollover
Millis.ino (1.12 KB)