Byron A Jeff wrote:
> On Fri, Sep 12, 2003 at 02:59:00PM -0500, Patrick Richards wrote:
>> This brings up the questions of how long an individual segment has
>> to be on, how quickly to refresh the display, and by how much you can
>> overpower each segment.  With 4 displays of 7 segments each, that is
>> 4 * 7 = 28 LEDs to light in turn.
>
> Yes.

Am I missing something here?  As I understand it, the OP wishes to
multiplex 4 7-segment displays.  The duty cycle for each display will be
25% as up to 7 segments (number 8) should be illuminated simultaneously
not in sequence.  Therefore I would deduce that he would wish to pulse
each display at 4 times the normal power (40mA) to maintain brightness.

>> So, at best, each LED is on 1/28 of the time.  This is neglecting the
>> time between turning off one segment and turning on the next.  If you
>> have an LED rated at 10mA displayed 1/28 of the time, do you need 28
>> times the power?  Surely not.  The LED couldn't handle it and we can
>> rely on persistence of vision to some degree.
>
> Correct. LED datasheets usually have a duty cycle to amp rating chart.
> 1/28 is about 3.5 percent duty cycle.
>
>>
>> As far as looping through the segments, I would prefer to use a
>> variable with one bit set low and then rotate the byte once per
>> segment instead of using a jump table.  Either way would work, but I
>> prefer seeing the logic in the code.
>
> As you wish! ;-)

I suppose that one could do it this way, but why?

>> If and when I get my code written for this project I plan to share
>> it. So, let's see who multiplexes segments first!  :)
>
> Cool. I look forward to seeing it.

Me too.  ;-)

michael brown

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