Mike, do you seriously believe that in some perverse way, it benefits your "reputation" by mendaciously mis-quoting the OP in order to confuse matters? This hardly constitutes "libel" on my part. :grinning:
My question is, is there a way that a PWM pin could be used to control the amount of resistance on the cathode side of the LED's? Theoretically, even though all of the LED's are on their own pin, they all connect to the same ground, and resistance (or anything like that) applied before connection to the ground would dim all of the LED's evenly.
As I have carefully explained, the answer is clearly "Yes!"
He cites a PWM pin. Now we could consider various esoteric ways of taking the PWM signal, using a low-pass filter to convert this to an analog value and using this to control a linear pass element in the negative side of the indicator LEDs. Clearly the problem here is that merely introducing a resistance or current limit would lead to a variation in brightness according to how many LEDs were illuminated at any one time.
But hey! It is a PWM pin, and you effect dimming using PWM. As I explained, it is entirely effective to simply switch the negative line en masse with the PWM signal.
The answer is then "Yes!" PWM controls the "effective" resistance to each LED (since it is in effect, switching each series resistor on and off simultaneously). That exactly covers "resistance or anything like that".
His real problem is not lack of PWM pins as he said "would dim all of the LED's evenly". He does not want to dim them independently (since for a start, 15 of them form a bar graph), so he does not require separate PWM pins.
The matter of driving a large number of LEDs is separate. Shift registers would indeed be an appropriate solution, and applying PWM to the output enable pin of the registers would certainly effect simultaneous dimming of all.
I trust he has considered the total loading of all the port pins - if many or most indicators are to be illuminated simultaneously, then the current limiting resistors would need to be selected for something in the order of 5 mA per LED (irrespective of the use of PWM) and this would apply similarly using shift registers unless you use power shift registers such as the TPIC6B595 (which is a cathode driver).