Quote Originally Posted by Art View Post
If you have rows of 12 LEDs parallel, that means they can't be independently controlled
for graphics, etc. You are just cycling whole rows of LEDs?
It's not for graphics. I am testing a number and the 12 LED's are one segment of the number.

Quote Originally Posted by Art View Post
The current can still be measured at 100% duty cycle, and as you lower the duty cycle,
the average current should lower approximately with the duty cycle.
Transistors have cut off slopes, so it's not extremely precise. Someone else may have to chime in about that.
However, just because you use say 50% duty cycle, the fact remains that the row of LEDs and hardware to drive
them are using the same current for half of the time, and no current for the other half of the time.
That's if you negate a little error for the actual switching on and off, but I don't know exactly what the cost is there.
I did some testing tonight but things still aren't clear for me. I will post the results below and maybe someone can derive something useful from this information. Brightness (how the user views it) is the ultimate test so I put a photocell on top of one LED and wrapped it in black electrical tape. I took random measurements with a bunch of tests using only PWM and the other using straight DC with a resistor. For clarification, the lower the resistance the higher the brightness.

Code:
LED'S ON	ON TIME	OFF TIME	CDS Resistance	DC Current	AC Current	Resistor	
1---------	5uS	        740 uS	92.2 Ohms	         36.4 mA	XXXXXXXXX	No	XXXXXXXXX
2---------- 5uS	        740 uS	94.2 Ohms	         41.3 mA	XXXXXXXXX	No	XXXXXXXXX
3---------- 5uS	        740 uS	98.3 Ohms	         52.6 mA	XXXXXXXXX	No	XXXXXXXXX
1+12 LED's	5uS	        740 uS	150.4 Ohms	         49.9 mA	189.3 mA	        No	XXXXXXXXX
1+12 LED's	5uS	        640 uS	141.2 Ohms        	 57.2 mA	214.2 mA	        No	XXXXXXXXX
1---------- 5 uS	        940 uS	118.4 Ohms       	 27.2 mA	XXXXXXXXX	No	XXXXXXXXX
1---------- 5 uS	       1140 uS	128.6 Ohms	          23.5 mA	XXXXXXXXX	No	XXXXXXXXX
2---------- 5 uS	       1140 uS	133.5 Ohms	         29.6 mA	XXXXXXXXX	No	XXXXXXXXX
3---------- 5 uS	       1140 uS	133.6 Ohms	         37.2 mA	XXXXXXXXX	No	XXXXXXXXX
1+12 LED's	5 uS	       1140 uS	194.8 Ohms    	33.4 mA	159.7 mA	        No	XXXXXXXXX
1+12 LED's	5 uS	        1240 uS	203 Ohms	        31.3 mA	154.6 mA	        No	XXXXXXXXX
1---------- 5 uS   	1240 uS	127 Ohms	         21.5 mA	XXXXXXXXX	No	XXXXXXXXX

1+12 LED'S	100	0---------	         109.2 Ohms	94.2 mA	XXXXXXXXX	Yes	29.6 Ohms
1+12 LED'S	100	0---------	         117.3 Ohms	79.9 mA	XXXXXXXXX	Yes	35.6 Ohms
1+12 LED'S	100	0---------	         136.1 Ohms	64.7 mA	XXXXXXXXX	Yes	44.5 Ohms
1+12 LED'S	100	0---------	         159.4 Ohms	49.3 mA	XXXXXXXXX	Yes	59.3 Ohms
1+12 LED'S	100	0---------	         201.6 Ohms	33.5 mA	XXXXXXXXX	Yes	89 Ohms
1+12 LED'S	100	0---------	         310.2 Ohms	17.1 mA	XXXXXXXXX	Yes	178 Ohms
I don't see much of a difference between PWM and using a resistor.