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I have to multiplex 12 digit 7 segment displays. How can i calculate the slowest time that i should show each digit, so i can see the 12 digit like they were all on?.
How are you planning to "scan" the multiplexed display? One digit at a time (1/12th or 8.3% duty cycle)? Or one segment at a time (1/8th or 12.5% duty cycle)?
This is important becuase it's difficult to produce good brightness with less than about a 10% duty cycle...
Refresh rate should be above about 50-Hz or you'll see the display flicker... If you're scanning segments (8 cycles for a full refresh), each segment should be on for no longer than about 2.5-msecs (50-Hz)... If you're scanning digits (12 cycles for a full refresh), each digit should be switched on for no longer than about 1.6-msecs (50-Hz)... If you select something like a 1.0-msec scan rate you should be safe with either scheme...
For a flicker-free display, you should use a scan frequency of about 50Hz. That is a period of 20ms, so each digit can be on for 20/12=1.66 ms. With some dead-time in-between, I would say 1.5ms per digit. That should be OK.
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