Altera FPGA DE0 PWM LEDS

[omerysmi]

Hello everyone,
I want to make PWM LEDS, i mean that pwm signal will control the intensity/brightness of the leds, such as this video: https://www.youtube.com/watch?v=83bEnZyirNQ

But how it could be possible when we have only '1' state which is 100% of brightness and '0' state which is 0% of brightness..?
With pwm I can only change the frequency of the led but not the brightness, am I right?

By the way I use FPGA Altera DE0..

 

[betwixt]

No, the frequency can stay the same (it can be also be changed if you wish) but should be high enough that the flash of the LED is quicker than your persistence of vision, this hides the flash and makes it appear continuous. Typically frequencies above a few hundred Hz are used.

The brightness is changed not by the frequency but the ratio, in other words the period within each cycle the output is '1' compared to the time it is '0'. If left at '1' you get 100% brightness, at '0' you get no light at all. By changing the time during the cycle spent at '1' to '0' you control the average light output. For example 50% on and 50% off will give an average of half brightness even through in reality, it is going from full on to full off during those periods.

Before someone comments, the average light output is proportional to the ratio but your eyes do not see a linear relationship between light intensity and perception of it.

Brian.

 

[omerysmi]

No, the frequency can stay the same (it can be also be changed if you wish) but should be high enough that the flash of the LED is quicker than your persistence of vision, this hides the flash and makes it appear continuous. Typically frequencies above a few hundred Hz are used.

The brightness is changed not by the frequency but the ratio, in other words the period within each cycle the output is '1' compared to the time it is '0'. If left at '1' you get 100% brightness, at '0' you get no light at all. By changing the time during the cycle spent at '1' to '0' you control the average light output. For example 50% on and 50% off will give an average of half brightness even through in reality, it is going from full on to full off during those periods.

Before someone comments, the average light output is proportional to the ratio but your eyes do not see a linear relationship between light intensity and perception of it.

Brian.

So what you say that i can change the brightness of the leds by changing the duty cycle of the wave?

 

[betwixt]

Exactly!

Think of it as (power * duty cycle) = brightness.

The frequency is relatively unimportant as long as it's high enough to prevent visual flicker but bear in mind that the efficiency of LED driver circuits may reduce if you go too high. For normal visual light dimming a frequency of say 200Hz up to a few 10s of KHz are used.

Brian.