Surface-Mount Light Breathes Life Into Your Project

Surface Mount Breathing Light PCB, using LM358 op-amp

If you’ve ever seen those gadgets with the “breathing light” LEDs on them and wondered how to do it, then [DIY GUY Chris] can show you how to design your own surface-mount version, using only analogue electronics.

Simulation trace showing the LED breathing light circuit operating. Traces for voltage and current are shown over a few seconds
The LED current tracks up and down in an approximately triangular-wave pattern

The circuit itself is built around a slow triangular-wave oscillator, that ramps the current up and down in the LEDs to make it look as if the lights are breathing in and out. The overall effect is rather pleasing, and the oscillation speed can be adjusted using the on-board potentiometer.

This project is actually an update to a previous version that used through-hole components (also shown in the video below), and goes to show that revisiting completed projects can give them a new lease of life. It also shows how easy it has become to design and order custom circuit boards these days. It’s not so long ago that a project like this would have been either made on stripboard or etched from copper-plated FR4 in a bubbling tank of acid!

If you have revisited an old project that you’re proud of and would like to show others, why not drop us a message on our tips line?

We have covered some other options for breathing LEDs in the past, such as this digital logic version, and this Arduino library that has a host of other effects to choose from, too.

13 thoughts on “Surface-Mount Light Breathes Life Into Your Project

    1. Well, nearly everyone else uses PWM because they want the LED to do more than just sit there and “breathe”.

      This circuit, as nice as the effect is, is a one-trick pony. It only does the breathing effect. It does it well, but that’s all it does.

      PWM is a cheap way of doing the same thing, not as “well”, but with greater flexibility such as being able to adjust the frequency, duty cycle or remain on/off.

    1. Actually, linear effects are usually not very pretty. But, because your eye sensitivity is not linear, you can use a linear effect for your lights and still get a pretty result. If you normalize it towards the sensitivity of the eye, it becomes less pleasing.

      1. This was not my experience when I coded up one of these years ago. I started with a linear ramp (using high speed PWM so as to appear more like analog) and it did not look right at all! It started very dark and quickly got bright and stayed bright. It didn’t look *linear* to my (log response) eye. So, I coded it to be exponential and it looked much better.

  1. Wanted to make a circuit for doing just this on cold cathode tubes and led strings back in 2001-2002 era and place them all around our server rack at work. I tried a pulsing current circuit but due to a lack of smarts I never got it working properly.
    Looked and looked but eventually just gave up searching as I couldnt find anything published to do the job.
    Essentially wanted the entire server room to ‘breathe’ at night.

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