[sdiy] 7-seg LED driving frequency

[Ken Stone]

basically, you need to go faster than the eye can see flickers at - approx
25 hz from memory. Most times the display is simply scanned at whatever rate
is conventient for the processor/program.  Make sure you turn off all
segments before moving to the next anode, or you will get ghosting.

Ken
>Hi,
>
>I'm making something that uses a triple 7-seg LED for its display.  The 
>3 digit LED has only 11 inputs (common anode per digit and common 
>cathode per segment), so you have to drive it at some kind of high 
>frequency.
>
>I plan to use a duty cycle of 1/3 per segment, but I don't know what 
>frequency.  I was thinking a pulse width of 0.1ms per segment (overall 
>update frequency of ~3 kHz).  But this is just a number picked out of 
>thin air.
>
>Does anyone have any experience with this kind of thing?  Are there any 
>pitfalls with using the wrong frequency?
>
>Seb
>
>P.S. The current will only be about 5mA per segment because I want to 
>run the whole circuit from a 78L05.  Hopefully the segments will be 
>bright enough - anyway I don't like really bright LEDs in my shady studio :)
>
>
>
_______________________________________________________________________
Ken Stone   sasami at hotkey.net.au or sasami at cgs.synth.net
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