[sdiy] LED current source needed for 'digital' outputs?

Tom Wiltshire tom at electricdruid.net
Tue Mar 4 19:07:59 CET 2014




> cheater00 wrote:
>> How does one achieve good control of
>> LED brightness without injecting HF trash into their audio output?

I drive the uP that's producing the PWM output and the LEDs from their own +5V supply. Audio finishes up on a +/-15V supply, so they're on completely separate rails. I usually also have two grounds (digital/analog), only connected at the power supply. I'm not trying to build a super duper low noise mixing desk or something, but I've never had any problems like this.

Another clue might be in the question - "HF trash". If you can keep the PWM frequency above audio, you ought to have enough roll-offs and band limiting that any noise would get significantly attenuated.

On 4 Mar 2014, at 16:41, Neil Johnson <neil.johnson71 at gmail.com> wrote:

> PWM is used because it is low power

Not only that. I like it because it gives me good brightness control over an LED using only a digital IO pin with no other hardware.

T.




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