[sdiy] What are these buttons?

[Tim Ressel]

O ho!  So that is what they are up to!  I've never played with one so I had no 
idea they were not buttons at all. Thanks a bunch!

--TimR




----- Original Message ----
From: "Speth, John" <John.Speth at coherent.com>
To: Synth-Diy <synth-diy at dropmix.xs4all.nl>
Sent: Wed, May 4, 2011 9:24:48 AM
Subject: Re: [sdiy] What are these buttons?

> I just saw the Tenori-On and am wondering what those buttons are?
> I'd like to
> use some lighted buttons in a project but the ones I have seen are
> very
> expensive.

I wondered about the Tenori-on too.  It's been discussed here before.  At that 
time I collected two very relevant PDFs about the technology.  You can find them 
temporarily at this dropbox:

http://dl.dropbox.com/u/23053666/nime2006_172.pdf
http://dl.dropbox.com/u/23053666/nime2006_342.pdf

LEDs have a lesser known function as crude photo detectors when they are reverse 
biased.  Capacitance is a function of light energy.  I'm sure there are many 
ways to measure capacitance but a really simple way is to do it as described in 
this EDN article:

http://www.edn.com/article/462289-LED_senses_and_displays_ambient_light_intensity.php


The beauty of using an LED as a photo sensor is that you can multiplex the 
detect function with the illumination function and emit light with it when 
you're not measuring its capacitance.  I've experimented with the method 
described in the EDN article.  It works.  I didn't attempt the illumination 
multiplexing idea but I think it's feasible.

It sure looks like the Tenori-on uses those methods to do its tricks.  It's a 
cool use of dirt cheap LEDs.  I suppose the cost challenge becomes obvious when 
you consider how to drive 256 LEDs faster than human eye persistence and detect 
touches rapidly enough using those same LEDs.

JJS


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