Thursday, 29 March 2012

A heart beat to midi converter

EDIT: This project actually finished up sometime in 2013. There is now a project page at, complete with a link to video of the device in action. You may want to go there directly.

Some while ago, David Usher approached Foulab about creating a device to convert heartbeats into midi signals.  Fortunately for us, he had already done a large part of the work and had got a hold of the optical pulse sensor recently featured in Make.

The pulse sensor shines a green light on the skin which is partially reflected onto a photosensor.  This outputs an analog signal, that, when conditions are right, indicates the intensity of blood flow beneath the skin, and thus to the heartbeat.  First tests were promising - modifying the Arduino code provided with the sensor to play a midi note was straightforward.  In the video below you can hear a note played for 50ms every detected heart beat.
First build is a bit ghetto, didn't even have a midi cable.  Also - note to self: dust the piano, sheesh.

One catch was that David wanted to take this on tour in a couple days.  Gapzap and I spent a crazy Tuesday evening putting together a robust project that would hopefully hold up in stage use.  In the end, the construction quality was pretty good (for which Gapzap should get most of the credit, I was up to my usual sloppiness, note the broccoli elastics).

Alas, it was for naught.  The sharp eyed readers will have noted the key phrase "when conditions are right" above.  They have to be exactly right.  In playing with it, David found sometimes it would work, sometimes not.  Some people it just never worked on.  And in all cases, the heartbeat was not as regular as you would expect - which might be a real phenomenon, the heart is not a clock.  You can hear this in the video, it seems alternately jumpy, then halting.  But in any case, it couldn't be played along with.

Still, not bad for a Tuesday night.  So that iteration was put aside, until its time for take 2.

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