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Optimal refreshing rate for 7-segment Displays

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swapgo

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Hi

I am using 3, 7-segment Displays Constructed with number of small LEDs
I am finding it difficult for setting the optimal refreshing rate.

Can any one help.


Thanks
Regards
Gopi
 

What is the difficulty? Simply increase the scan rate until the flicker disappears.
 

Try with 9ms for whole cycle... ( every 7 seg works 3ms).
In 7 seg datasheet read which current should be, per diode, and see if ressistors ere choosen properly.
 
Also, remember that if the LED are rated 10mA (for example), if you drive them 1/3 of the time, it will only light 1/3 of the power.

LED are beautifull thing for that is you can put higher current, if the duty cycle is low. For example, you can run them with 30mA, 1/3 of the time. But make sure though that your system actually does toggle between the digits, and does not get stck at one of the digit.

Note though that there is a limit on the ammount of current you can put in that way, and that the voltage drop may be a bit higher across the LED. Check with the datasheets.
 

swapgo said:
Hi
I am finding it difficult for setting the optimal refreshing rate.
Click to expand...
For Human Eye?

Rule of Thumb: Watch an incadescent lamp to flicker or not then give some higher reasonable values of frequency to your LED if you are supplying the AC. Remember LED's are diodes and conduct/emit light in half cycle.

One more thing even if we do not like to see the incandescent lamp because it hurts our eyes you better choose a much higher frequencies for refrech rate.

It has occured to me to notice flickering of LED's even when frequency was 2kHz.
 

every LED should be "refreshed" at least 30 times per second
 

The statement by djalli about noticing the rate is important. Tests have been done which indicate that even rates that cannot be notices cause fatigue if they are examined frequently. This is why, according to tests done by psychologists, florescent lamps that flash 100 or 120 times a second cause fatigue and the higher frequency inverter driven ones do not. It is part of the eye movement. The eyes scan lateral motion in little jumps which start and stop when the light comes and goes. If the inverter is high enough in frequency, there is no flashing because of the decay of the phosphors in the florescent lamps.
 

I have used 200 Hz refresh with good result. As said above you could increase the current a little bit to still have bright results
 
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