Can someone please clear up a query I have on multiplexing. I've just spent a stack of time trying to learn to program an arduino to study the effect of:

1. 
   When multiplexing 2 seven segment digits, what is the lowest delay required so that I don't see the "flickering"
   Same with 3 seven segment displays
   Same with 4
   Also what is the intensity difference with having 2 digits multiplexed vs on full time
   Ditto with 4 digits

I believe from what I've read that the delay should be around 30 frames per second. Does this mean a delay of 33/1000 sec for 2 digits? I seem to have to type in 10 in my code for it to stop the flicker (not 33).

For 3 digits I need to set the delay to 7 and for 4 digits, a delay of 3. Can someone please tell me the maths for this.

I've also uploaded a video of my code running (see link below).

http://m.youtube.com/watch?v=3-VcqghIb9k&desktop_uri=%2Fwatch%3Fv%3D3-VcqghIb9k

If anyone's interested in the code, see attached file...
View attachment Multiplex example.txt

 

I use pic programming, and have a delay of 2 millisec , and call it 50 times in total , so each segment is on for 100 millisec in total, it works upto 5 digits, for more digits i would use a cd4511 segment decoder driver, no multiplex required.


so digit 1 on for 2ms (digits 2-3 off),
then digit 2 on 2ms, (digits 1-3 off),
then digit 3 on 2ms, (digits 1-2 off),

do this 50 times

 

I use pic...a delay of 2 ms...call it 50 times...each segment is on for 100 millisec in total...up to 5 digits

Sorry, still not 100% sure...

So the delay time for each you have as 2ms.
If 5 digits, then 1 loop = 5 x 2 =10ms.
I would assume this repeats continuously, so in 1 second it loops 1000/10 = 100 times.

So does that mean that the frequency for each individual digit is 100 times per second each (i.e. 100 loops x 2ms x 5 digits = 1000ms)?

If this is correct, based on movie film rate being set to between 26 to 30 frames/sec, wouldn't this mean the fequency for 5 digits could be 1000/(30 x 2) = 6.6ms delay each? Or does a digital led display need a higher frequency than film?

 

If your worried about multiplexing, use the cd4511 cmos drivers, easier to use just put the binary value to each chip, set the latch, then move to the next segment, and so on,the chip will hold the value until it is refreshed with the latch pin. As for the multiplexing each digit is on for 2msec, the more times you call the display routine the less flicker,i have used it upto 4 digits and called it 125 times, so each digit is on for 2msec, off for 6msec, 8msecX 125=1sec.


5 digits would be on for 2msec off for 8msec, 10msec total time do that for 100 times = 1 second
or better use the cd4511 chip

 

Ok, that's makes more sense. However it doesn't equate then to frames (flicker) per second. 4 digits - 125 times per second - therefore each digit is on 1/4 of the time.

I've found that they digits are considerably dimmer. Do you know if it's therefore 1/4 the intensity? If so, can I up the current to each digit (reaching the peak allowable, so as to compensate - as I want these digits visible outdoors in sunlight.

As for the 4511, in my previous 4 digit counter, I used 2 x 4518 dual BCD counters with four 4511's. However, this time I'm trying to achieve the same with less circuitry and greater flexibility. Am I steering in the wrong track trying to not use 45xx's?

As another option, can I use port manipulation to overcome the intensity drop of the digits? If so, any ideas where I can look for comparible code?

 

I would use the cd4511 chips, that will give you max brightness,no hassle with muxing.