drive some led which all light intensity seem the same

hi every one,
I'm using a circuit which has 2 7segment but I use 7 LEDs instead of each 7segment. this 7segments shows numbers from 10 to 35 and because of supply current limitation Just 2 LEDs can be on each time so I have to use PWM signal to turning on them. Consider I want to show 28 so 12 LEDs should be on and as I mentioned just 2 leds can be on. I show the signal which I use to turn on the LEDs on figure 1.
my first problem is what is the best value for x that eyes of human didn't detect wink and the light intensity of LEDs is high enough?
my second problem is if I use the same way for showing 11, the light intensity of LEDS will be more! because for showing 11 just 4 LEDs should be on and it would be like figure 2 and Specifically the light intensity of LEDS will be more because less time LEDs would be off, so I think I have to change x for each number but I don't know how to calculate x for each number that the light intensity of each number will be the same.
could you please help me?
Regards
Matin

Hi,

The average current consumption and intensity depend on each other.

PWM reduces average current and average intensity.

You could reduce segment current to 10% or you could use 10% PWM.
Both result in the same 10% average current and in 10% intensity.

Klaus

Are you connecting Mosfet to common cathodes or anodes and driving the mosfet from PWM ?

If yes, map the Led data bus data to pwm duty.



Edit:


If you have 8 Leds and their cathodes are shorted and connected to drain of Mosfet and Mosfet source is grounded and gate is connected to PWM output then

For 8 LEDs duty is 100% = 255 in mikroC
For 0 LEDs duty is 0% = 0

y = mx + c

duty = m * 8 + 0

255 = m * 8

m = 255 / 8

= 31.875

duty = no. of leds On * 31.875

map the mask value to no. of leds On in switch statement and accordingly assign duties