Hi Dave,
I specifically made this turn that last LED off rather than fade it. That is done by this line:
if (current > 19) charlieON(19); else charlieON(current);so rather than the focus LED which is the head of the animation going off the bottom, it stays at 19 until the animation is complete and the tail has collapsed into it. If you want the head to keep going so the last LED fades, change that line to simply:
charlieON(current);
If you want the last LED to fade after the tail goes away, suggest you use the charlieplexing duty cycle to do that. If the Analogwrite is working that is simply good fortune that the particular ATTiny pin referenced in the array at that point is one of the PWM pins. That won't work the length of the array therefore since one of the 5 pins used for controlling the LEDs isn't PWM capable.
I'm surprised by your findings on the randomseed(). Analog pin 0 is actually leg 1 on the chip, which is disconnected. My thoughts were that worst case, even if it always returned the same value as that seed it will still generate a pseudorandom sequence, though it will have a sequence that will repeat every run. It isn't electrically connected to the LEDs so I need convincing it can be playing a part in flashing any lights.
I am not seeing your issue, as yet. Will try to break it tomorrow and report back.
Geoff