Oscillator Clock Rate
The clock rate can be set to 8Mhz or 4MHz using the Arduino IDE.
Using 8Mhz will provide the best IR performance, while 4MHz may provide a longer battery life. Do not use any other clock rate.
Note: The granularity of the Arduino micros() function, increases as the clock rate changes from 16MHz to 8MHz to 4Mhz to 1Mhz. This has a knock on effect on the IR signal timing. Running on batteries, 16MHz is out of spec & at 1Mhz the IR performance is materially impacted by the granularity of the Arduino timing.
Thus we strongly suggest using 8MHz as the default clock rate, which provides a good balance between IR performance and battery rate. If you know your way around low power operation & want to drain the last bit of juice from the batteries ,then it is Ok to consider 4MHz. In our opinion, it would be preferable to swap out the batteries a little sooner and enjoy the better IR performance/experience.