Reverse engineering the Mac ‘breathing’ LED

Repost from 2006!


For the Duel nature sculpure, I wanted to have a ‘breathing’ pattern where all the LEDs vary in brightness in a natural/organic way. A good example is the ‘sleep indicator’ LED on recent Macs/Powerbooks. (There’s even a patent!) The problem is that, while the patent claims its a simple sinusoid (see the patent for the image), programming in a sinusoid doesn’t look nearly as good. So I decided to get the real waveform with a kludgy reverse engineering attempt:

[flickr 212611715 ]I used a MIDIsense instead of a simple voltage divider because I want to extract the absolute LED brightness pattern and a photocell voltage divider acts ‘inversely’ (well, 1/R) instead of linearly (ie, just R). (The MIDIsense has an opamp to linearize the resistive sensor output)

[flickr 212611654 ]

There it is! There is a bit of ‘noise’ on the peaks because I’m picking up some of the PWM artifacts through the diffused white plastic.


As 2022 starts, let’s take some time to share our goals for CircuitPython in 2022. Just like past years (full summary 2019, 2020, and 2021), we’d like everyone in the CircuitPython community to contribute by posting their thoughts to some public place on the Internet. Here are a few ways to post: a video on YouTub, a post on the CircuitPython forum, a blog post on your site, a series of Tweets, a Gist on GitHub. We want to hear from you. When you post, please add #CircuitPython2022 and email circuitpython2022@adafruit.com to let us know about your post so we can blog it up here.

Stop breadboarding and soldering – start making immediately! Adafruit’s Circuit Playground is jam-packed with LEDs, sensors, buttons, alligator clip pads and more. Build projects with Circuit Playground in a few minutes with the drag-and-drop MakeCode programming site, learn computer science using the CS Discoveries class on code.org, jump into CircuitPython to learn Python and hardware together, TinyGO, or even use the Arduino IDE. Circuit Playground Express is the newest and best Circuit Playground board, with support for CircuitPython, MakeCode, and Arduino. It has a powerful processor, 10 NeoPixels, mini speaker, InfraRed receive and transmit, two buttons, a switch, 14 alligator clip pads, and lots of sensors: capacitive touch, IR proximity, temperature, light, motion and sound. A whole wide world of electronics and coding is waiting for you, and it fits in the palm of your hand.

Join 32,000+ makers on Adafruit’s Discord channels and be part of the community! http://adafru.it/discord

Have an amazing project to share? The Electronics Show and Tell is every Wednesday at 7pm ET! To join, head over to YouTube and check out the show’s live chat – we’ll post the link there.

Join us every Wednesday night at 8pm ET for Ask an Engineer!

Follow Adafruit on Instagram for top secret new products, behinds the scenes and more https://www.instagram.com/adafruit/

CircuitPython – The easiest way to program microcontrollers – CircuitPython.org


Maker Business — Pololu’s account of the chip shortage

Wearables — Monster-inspired costuming!

Electronics — How to make your own magnetic field probe!

Python for Microcontrollers — Python on Microcontrollers Newsletter: New Releases of MicroPython and CircuitPython and more! #Python #CircuitPython @micropython @ThePSF

Adafruit IoT Monthly — 2021 in Recap!

Microsoft MakeCode — MakeCode Thank You!

EYE on NPI — Maxim’s Himalaya uSLIC Step-Down Power Module #EyeOnNPI @maximintegrated @digikey

New Products – Adafruit Industries – Makers, hackers, artists, designers and engineers! — New Products 1/19/22 Feat. Adafruit 7-Segment LED Matrix Backpack – STEMMA QT / qwiic!

Get the only spam-free daily newsletter about wearables, running a "maker business", electronic tips and more! Subscribe at AdafruitDaily.com !



5 Comments

  1. Could it just be abs(sin(w*t)) ?

  2. I would just go for the actual LED driving signal since that would be more useful for replicating the effect. LED brightness doesn’t correspond linearly to driving current. Also, diffusion material would never smooth or deteriorate the PWM signal. Phosphor, such as used in white LEDs, might smooth it a little.

  3. certainly between 12-20 breaths per minute

  4. Funny that it’s patented. I wonder if that’s why my Dell has such an un-natural, ugly pattern.

  5. It’s probably exp(sin(t)) to correct for the logarithmic response of the rest of the optical system (LED->eye->brain).

    http://www.wolframalpha.com/input/?i=plot+exp%28sin%28x%29%29

Sorry, the comment form is closed at this time.