[sdiy] 7-seg LED driving frequency

[Seb Francis]

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 :)