[sdiy] 7-seg LED driving frequency

[Seb Francis]

Thanks Ken & Simon for your answers.

Going by my experience of 'comfortable' CRT monitor refresh rates I 
would say that I should run it at 100Hz+ to get rid of any perception of 
flicker.

But I was wondering whether I should try and run it above audio 
frequency to try and avoid audible noise coupling into the power 
supply?  Maybe I am worrying too much about nothing :)

Seb


Ken Stone wrote:

>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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