It seems that the jaydeep might have been building my circuit and used the provided code: http://www.instructables.com/id/Arduino-controlled-light-dimmer-The-circuit/step4/Arduino-controlled-light-dimmer-The-software/
so obviously this problem has my interest.
With regard to the 'dimming' variable, that will not go beyond 128 so I might as well have used 'byte' to define it.
The IR remote library is I presume that of Ken Shirrif and that one uses the Timer2 interrupt. In principle, combining those two interrupts shouldnt necessarily cause a problem as I have done so as well (in using the timer interrupt rather than 'delay to trigger the TRIAC).
But in that case the entire timer interrupt was handled within the period of the mains wavelength (100 or 83 ms depending on frequency).
I don’t think the access to the 'dimming' variable -as jfpoilpret mentions- is the problem (though he makes some sound remarks), as that will just remain as is for a specific light level.
The problem -as is also suggested above- might well be in the fact that the IR receive takes too long.
So... disregarding interrupt priority for a moment, if the code is hanging around in the timer interrupt routine and there is a zerocrossing, that won't be detected, or, if the code is just doing a zero crossing detection, the timer is screwed up.
In comes interrupt priority: The external interrupt has the highest priority (other than reset). So.. when the IR receive routine is busy in the Timer service routine and a zerocrossing arrives, it will be taken out of that routine, zerocrossing will be handled and ideally, it should continue with the timer routine again.
However, your remote has no idea what is going on in the Arduino and some of the code sent will be missed.
all of this shouldn’t need to be a problem if the external interrupt was fast, but as most of the waiting is actually done within this interrupt, it could take up to almost 10mS/8.3mS (when 'dimming' approaches 128).
Well, I can't say much about the Timer2 interrupts in Ken's library, But on 'my side' of the software, what could be done is to shorten the external interrupt by removing the delays and use (yet another) timer interrupt.
Ken uses Timer2, so this would have to be timer1.
So, whenever there is a zerocross, there is no waiting in a delay, but it will be handled by timer1
An example is given in Step 6 of my instructable. There is no guarantee this will work but there is a good chance
Let me just point out that the basic program I supplied was just given as an example, It uses much computer time in waiting and therefore isn’t the best to combine with other actions of the processor.