Hi, I am trying to make a project that involves an LED "breathing", something similar to this: http://thecustomgeek.com/2011/06/17/breathing-sleep-led/

Except, instead of turning off at the end of the cycle, the light will stay on at around 61% brightness, then fade back to 100%, and so on. Is there a way to do this? Would I need a 555 timer instead?

 

Here is a single bjt driver circuit, with explaination, that could connect to 555 output.

https://www.youtube.com/watch?v=A-EEppHIzxs

 

You can see the author's code here. It is merely a loop that ramps up the value to the PWM (my assumption), waits varying amounts of time depending upon the value sent to the PWM, and after running through the loop, repeats. You can change the maximum and minimum apparent brightnesses by changing the value of the first argument in the FOR statement in both places it appears in the code.

ORIGINAL:
for(i = 15 ; i <= 255; i+=1)

MODIFIED SO IT WON'T GET AS DIM:
for(i = 60 ; i <= 255; i+=1)

Keep in mind the fact that to a human eye apparent brightness is a logarithmic function of optical power and is highly affected by the degree of light/dark adaptation of the visual system.

The original Arduino sketch:
http://www.thecustomgeek.com/files/Sleep_LED.pde

 

I think I'd send a slow cosine wave through the PWM, but "clip" all values that fall below the minimum threshold, holding them at the minimum instead of allowing them to fall. That will give that slight hold time at the minimum value before it throbs again.

Note that "throbbing" is a good search term for this sort of thing.

 

Hello,

What do you think of led "flames":
http://www.schakelingenonline.nl/schakelingen/lichteffecten/9.htm
As the page is in Dutch , I translated the page using google:
https://translate.google.com/transl...l/schakelingen/lichteffecten/9.htm&edit-text=

Bertus

 

Or look at, forum.allaboutcircuits.com/showthread.php?t=98511 , xkillowatts, 6-10-2014
Vary R3 to change minimum brightness.

 

Here is a circuit using a 555 timer , speed is centered around 3 seconds on/off.

 

Dodgydave, I assume the line cross at pin 2 & 6 is a connection?

 

Dodgydave, I assume the line cross at pin 2 & 6 is a connection?

yes, pins 2,6 together to make an astable.