Thank you heart

(This is a quick overview.  Proper build details will follow soon.)

I wanted to put something nice in the window to say “Thanks!” to all the health care and other essential service workers who are keeping people safe and helping life go on in these challenging times.  Sorry it’s starting so late.

Electronics

The heart is some 200 WS2812 individually addressable RGB LEDs mounted on a heart-shaped ring of 1/4″ foamboard.  They draw around 4A from a 5V supply.  An Arduino Pro Micro drives the LEDs thru the Adafruit Neopixel library.  Thanks, Adafruit!  I wrote the code telling it what to do in C/C++ using the Arduino development environment.

Appearance

There have been lots of changes in plan in the 2 weeks between starting and hanging it in the window.  One of the very visible ones is naked vs diffused LEDs.  What I envisioned from day one was a smooth, gentle glow.  I didn’t want the techie appearance of raw LEDs.  The tracing paper diffuser on the left half gives just the visual effect I wanted.

But both my wife and I responded to the brilliant LEDs on the unfinished side.  The phantom-of-the-opera-mask appearance was never planned, but it’s an interesting feature.  While the option of putting the diffuser on the right side remains, I’m guessing it won’t happen.

Behavior

In keeping with the ‘gentle glow’ spirit, the plan was to light the heart with just one color, changing slowly around the color wheel maybe once/day.  Fancier opportunities arose, and alternating days of full saturation and pastels was the plan for a while.

Early in the software development (meaning after it would actually light up), various animations from the Adafruit example code were included.  Other patterns suggested themselves, and although envisioned as static displays, I typically prototyped them as animations, often to help debug code trying to get the LEDs to behave in ways foreign to their linear addressing scheme.

But as we watched it cycle thru the animations still in the shop, I had to admit that it seemed a shame to deprive its audience – neighborhood walkers – of the entertainment of the dancing patterns.

So in a near-complete reversal of the original plan, V1.0 spends most of its time slowly but visibly changing color, with a spot of eye candy animation every 20-40 seconds.

Making it

Frame

While I did have to order a new spool of LEDs, the rest of the parts, including the Arduino and power supply, were just on the shelf.  That meant that the main frame was cobbled together from 6 bits of scrap foamboard.  There were mechanical challenges piecing them together.

LEDs and reflector

The obvious thing to do was to just stick the adhesive-backed LED strip to the foamboard.  Unfortunately, while the strip is quite flexible in one direction, it’s quite inflexible in the direction needed to make it conform to the curves of the heart.

But if I laid the strip on its edge instead of its back, I could easily bend it to follow the heart shape.  I could just glue some little blocks to the foamboard to anchor the strip right where I wanted.  Great!

Well, except then the light coming from the LEDs is going the wrong direction.  If I put a mirror at 45° in front of every LED, I could bounce the light right back where I wanted it.  Some back of the envelope calculations to determine how big the reflector should be, and a plan emerged.

The initial attempt using aluminum foil was way too flimsy, and didn’t work well at all.  Fortunately, I had a big roll of very shiny adhesive foil tape, and lots of 110 lb cardstock.  Based on the dimensions that looked like they’d work, I made up a bunch of cardstock-and-foil-tape 45° reflector strip.

 

Lots of snips and tucks and glue and adjustments later, the LEDs were shining the right direction.  Here looking straight down on the foamboard, you can see just the edges of the actual LEDs (circled) and their reflections in the foil.  Not perfect, but most of the light is going the right way.

Diffuser

To get the “soft glow” I wanted – long before the half-and-half idea raised its interesting head – I found supporting a sheet of tracing paper over the (reflections of the) LEDs worked well.  A couple of design iterations later, I had a support approach that looked like it would work.

Twelve sheets of tracing paper, a bunch of supports cut from PET packaging, two kinds of glue, and a couple of hours later I had a nice gentle light from half of the heart (plus carefully cut paper for the other half – which will probably never be installed).

Next steps

While the heart is finally in the window, it’s very much still work in progress.  I’m sure it will learn new animations as ideas come up from others (or me!).  It still needs to learn what time it is to automatically fade up in the morning and fade out at night.  Motion detection from the existing cameras may affect its behavior.  Fortunately, teaching it new tricks now doesn’t involve glue or Xacto knives or clamps:  “It’s just code from here.”

Comments are welcome.

Thanks to all our heros who are working to keep us safe and sound!

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2 Responses to Thank you heart

  1. Jim Harvey says:

    This probably won’t apply to your LED heart but I did some experiments with conventional plastic lens headed LEDs. If you file the lens off so it’s flat, the light is much more widely distributed. And if you file the lens off at an angle, more light gets sent out sideways.

  2. Jim Williams says:

    Yeah, I’ve filed ’em down to get better distribution. (Read: to defeat the nice optical engineering that went into the design of that lens.) But I hadn’t thought about asymmetrical grinding to get asym distribution. Cool – thanks!

    Hope you guys are staying safe.

    Jim

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