How to control the brightness of a LED using PWM?

[Rooftop]

Designing led with PWM

Hi all,

i have 8*8 led and with that i want to display an alphabet(with scanning) so how to control the brightness using PWM?
Someone have idea?

 

[IanP]

Re: Designing led with PWM

In standard application you select a row and then a column and LED located at the row/column address will be on.
Now, if you modulate one of these signals with PWM (the PWM frequency has to be higer then the scanning frequecy, say 10:1) you will be able to control brightnes of the LED array.

 

[Rooftop]

Re: Designing led with PWM

Thanks for the reply.
I using db25(paralel port to access the led) Do you have some idea how to use pwm(It's like sampling a square signal right?)
I use control signal (C0,C1,C2) for the scanning.
Thanks

 

[Frikkie]

Re: Designing led with PWM

Thanks for the reply.
I using db25(paralel port to access the led) Do you have some idea how to use pwm(It's like sampling a square signal right?)
I use control signal (C0,C1,C2) for the scanning.
Thanks

That is right. The faster the switching the more brighter the LED become.
The slower the less brighter it becomes. But if to slow then youre LED will show a flash.

For access turn the port line on and off. |_|-----|_| long |_|-|_| short.
The short should be the less brightess. Just remember to make the off period not to long.
This will show a flash.

:sm35:

 

[Rooftop]

Re: Designing led with PWM

Yay... thanks for the repply,now i will try it

 

[qutang]

Designing led with PWM

use a sine wave to control the light,I think like this.