I don't understand the blue part of your statement. With a bank of 5x6 LEDs each LED will be on for 1/6th of the time. However, LEDs can normally be pulsed at 2½ times their steady current and so in reality they receive nearly 50% of their maximum current. This is the same as any multiplexing routine except charlieplexing uses less I/O pins.
Mike.
We have been down this road earlier.
Maybe you can convince me I am wrong.
It depends on how you arrange the current limiting resistors. If one put a resistor on each LED or used LEDs with built in resistors one could light any combination of LEDs within the bank and have the same brightness. In this case what I am saying is bull, but these is still an issue about where the current come from.
If you sink or source several leds through a single PIC pin as charlieplexing does the current through each LED will be a fraction of what each pin can deliver. With a regular multiplexed display you can use a transistor to overcome this. With charlieplexing the current can flow either way. It is not so easy.
Most of the time only N resistors are used. As the number of illuminated LEDs increases the current through each LED goes down. Like using a single current limiting resistor with several LEDs. So you can only get uniform illumination if you light 1 LED at a time or sequential.
That is why I thing they should be used sequentialy within each bank.
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But going back to the math. Even with the 2 1/2 current overdrive a six bank display will not be full brightness.
(5/2)*(1/6) = 5/12 of less then half the current. With the visual log response as suggested by hero999 you may see 75% brightness.
Also the OP was talking 30-50 so 6 lines is only for the lowest case. To do a full 50 requires 8 lines.
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If I am full of bull please let me know.
3v0