peter green wrote:
>>> but i really don't see the point in using two extra chips when 
>>>       
>> you can easilly get a PIC with sufficiant pins to do it without 
>> much help (still need the transistors on the common lines)
>>     
>>>   
>>>       
>> again, in theory the PIC will provide enough current, but the result 
>> will be dim because the PIC can only sink 25mA; in a multiplexed 
>> arrangement the current needs to be on the order of 60-200mA
>> to be bright enough.
>>     
> ouch, what kind of displays are you building to need that kind of power?
>
> for a 6 digit system with normal sized displays used under household conditions i'd think a 330ohm series resistance (~10ma drive) would be perfectly bright enough, especially if you cover the displays with a filter (filters hugely increase your contrast ratio and make the display look nicer too, highly reccomended).
>
> one final note, don't start driving LEDs over thier rated max continuous current until you are very confident you have your software right, the last thing you want is your code hanging and frying a display.
>   

Hmmm. No point in arguing. Why don't you try it and see what you need?

You see, the eyes are not deceived by multiplexing. The "apparent" 
brightness at 10mA will be invisible in daylight. Try it and decide for 
yourself.

Maybe the filter will help.

--Bob
>
>
>   

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