[sdiy] Will LCD backlight PWM cause audio noise?

[David G Dixon]

> If I control the brightness of an LCD backlight using PWM, is 
> it likely to cause a lot of audio noise?
> 
> I was planning to have a PIC PWM channel driving a transistor 
> to switch the backlight on and off. This could be well above 
> audio frequencies, say 78KHz. However, it struck me that 
> switching a high current load (30-40 mA) on and off rapidly 
> right next to a load of sensitive audio circuits wasn't the 
> brightest idea I'd ever had.
> 
> What do you think? Will it cause me problems or will I get 
> away with it?

I think you'd be very lucky if this didn't cause some issues.  At the very
least, you should apply rigorous rail decoupling at the source of all the
digital signals.