Delay timer in function without delaying main loop!

[rickkas7]

This is a minor thing, but a good habit to get into. When you compare against mills, always do it like:

if (millis() - lastTime >= TIME_INVERVAL) {
     lastTime = millis();

The reason is that millis() rolls over, or resets to 0, every 49 days. If your code runs for 49 days, the test written the other way will fail, but the test written this way continues to work properly.

The reason why has to do with how unsigned numbers are represented in C, and a topic of an entire post:

Millis() and rollover tutorial

The millis() function is handy for timing things with the Particle Photon (and Electron, and Core). It executes very quickly and has a good resolution (milliseconds). From the manual: Returns the number of milliseconds since the device began running the current program. This number will overflow (go back to zero), after approximately 49 days. Note: The return value for millis is an unsigned long, errors may be generated if a programmer tries to do math with other datatypes such as ints. Now…