Digital signal processing with teeny-tiny tap-dancers.

When we wrote about accelerating Fast Fourier Transforms (FFTs) on the Pi back in January, several people asked what sort of real-world application FFTs can have. We talked about numerical analysis, cryptography, spectrograms and software-defined radio, among other things, in the comments on that post. All the same, FFTs are something that those who don’t get excited by maths can find a bit dry, and it can be hard to find a good demonstration of FFTs that works for those of you who like to think about things visually. So I was really pleased to find a link to this project from Pavan Tumati, which makes digital signal processing…decorative. Not to mention festive.

Here, FFTs are performed on music samples on the Raspberry Pi fast enough to detect a beat, and the Pi relays that information to some teeny-tiny tap-dancers, who produce an automated routine that’s synced to the music.

These little tap-dancing guys are from a post-Christmas sales bin. They’re called Happy Tappers, and are made by Hallmark, who, for reasons known only to them, include a port which enables them to interface with their tippy-tapping brothers and sisters – which makes for exciting DIY project possibilities once you add something that’s able to feed them an input. I’ve never seen them on sale in the UK, but if you’re dead set on making your own tap-dancing Pi project, they seem to be available online at eBay, Amazon US, and at some Christmas shops.

(I know: it’s a bit odd posting about Christmas decorations in mid-March. But if the family across the road from me, who still have multicoloured lights flashing away merrily on the tree in their front garden every evening, are anything to go by, Christmas decorations aren’t just for Christmas any more.)


Jim Manley avatar

When left up after the first week of January, they’re officially no longer “festive holiday lights”, but an indication that the residents are full-fledged, card-carrying members of the International Procrastinators Club, which will be holding its first organizational meeting if/when they get a Round Tuit. What, you don’t have “Christmas in July” stores there? That explains the extreme jet lag – you need to so thoroughly confuse your bod about what proper seratonin levels in the brain are that you don’t occupy any time zone! :lol:

Now, off to hunt me down some tiny tippy-tappy dancers (I hope Google doesn’t choke on those for search terms!) ;)

Jim Manley avatar

Blimey! They’re going for more than half the cost of a Pi … EACH! They were on sale for as little as $7.50 back in 2012, but I guess this is a lesson in inflation, supply and demand over time, and another facet of the Raspberry Pi Effect on world commodity prices! :lol:

Haggishunter avatar

Sweet! I was nearly a founder member of that club! How did somebody else beat me to it?

AndrewS avatar

I keep meaning to join…

Alex Eames (RasPi.TV) avatar

Fantastic. That is ‘brilliantly silly’ (which is a very large compliment, in case it could be taken the wrong way.)

paddy gaunt avatar


I’m using fft in out pi3d related devart entry ‘playful geometries’

see a kind of prototype here

I am constantly amazed at what the RPi can do. In that video it’s basically:
a. running python, a sluggish interpreted language.
b. also running flask web server. i.e. serving proper web pages with all the twiddly bits not raw socket stuff
c. Also running mpg321 playing non-crackly, good quality mp3 files out of the din socket
d. which is ALSO doing real time fft analysis and feeding the information back to the python app.
e. which is ALSO running 30fps 3D animations at full screen using algorithmically generated textures in opengles shaders.

Did I mention that I was amazed by it.

By the way, the plan is to have several screens around the room showing a different view of the 3D animated scene which visitors can alter using tablets etc.

Zack avatar

Very cool video!
How do you do FFT analysis on a audio stream?

paddy gaunt avatar

I’m doing it as a python subprocess here but basically just
$ sudo apt-get install mpg321
$ mpg321 -R -F junkname
load musicfile.mp3

Jim Manley avatar

I’m tellin’ ya, Paddy, someday this Pi thing is gonna catch on and they’re gonna sell millions of ’em, especially once people find out it can do 3-D via GPU acceleration – just mark my words! :lol:

The remote stuff is eye-popping, but I doubt more than a handful of people will be able to grasp what’s actually going on. That’s OK, more GPU cycles for those of us who know what to do with them! ;)

Rick avatar

Christmas Decorations seem to stay up all year round in St Albans these days. The Water End Barn hasn’t taken theirs down, and the council dont even bother taking the main ones through the town down anymore.

Then there all the houses who thought it’d be a good idea to buy solar LED lights to put on their garden bushes and trees, and you guessed it – they’re still on.

Graham avatar

Anyone have a link to the working video? I just get a black square for the ones in the article and linked project.

ameyring avatar

It happened to me as well, but when I just let it load for a while, the video came up.

Steffen avatar

That clip saved my day :)

richard77 avatar

Today is Pi day in US, and we are in Pi month for the rest of the world (the only Pi month of this century!)

The Other Peter Green avatar

xkcd’s recent take on ‘special’ dates… :lol:

paddy gaunt avatar

every day is pi day. But it might take more than a day to figure out what base to express pi and the date in!

meltwater avatar

Now to scale it up using electrodes and Pi-Team members…

AndrewS avatar

LOL! You’ve just reminded me of the RI Christmas Lectures where they were applying a large magnetic force to someone’s head, which interrupted their brainwaves and caused their arm to spasm.

…aha! It wasn’t an arm, but it does still tie in (vaguely) with the Christmas theme :-D

Pavan avatar

I’m the author of this side project. :-) I appreciate the compliments.

Thanks Liz, for the link. The energy and enthusiasm in the Raspberry Pi community makes working with the hardware quite fun.

liz avatar

We thought it was bleedin’ awesome. Thanks so much for sharing the project; we really enjoyed it!

ColinD avatar

Today was a normal day… then I watched the Happy Tappers dance. Now my sense of reality is warped.

Fantastic re-use of pointless tech :)

Craig avatar

Still being a NOOB at all this Pi stuff…
Can I presume it could be made to work with one of these ?

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