Is there a real need to use an interrupt to switch to the next frequency?

[John-Lluch]

You use an interrupt to determine the time to change to the next frequency. However the actual frequency change is performed on the main loop. I understand interrupts are used to get a precise 'interrupt_time' of 10 ms intervals to set the next frequency.

However I think that given how it works you should be able to do the same by just storing the last millis() as a multiple of 'interrupt_time' and checking whether the next millis() multiple is greater than that. I think it works the same as the 'fired' variable in your code because millis() value is interrupt-generated anyway.

That approach would greatly simplify the code and make it more portable. Does this make sense to you?

Thanks