led's as touch sensors

[quantumonkey]

i've been looking into making some sort of alternative midi controller for a while now and found the following sites

this one using leds as touch sensors looks like a very interesting design idea

http://mrl.nyu.edu/~jhan/ledtouch/

a few more relating to the above,

http://forums.linear1.org/index.php/topic,445.0.html

http://www.merl.com/publications/TR2003-035/

http://projects.dimension-x.net/technology-and-projects/ledsensors/

this project is amazing    http://nnnnnnnn.org/index.php?n=0001

look at the video.....http://music.calarts.edu/~tehn/(tehn)mlr.mov

just interested in what you guys think of these projects

i do hope to build a midi box project but these are definitely  too far out of my reach, but maybe someone here will be interested!/inspired!

[pay_c]

Very very interesting! A lot of stuff to read first, but indeed a very interesting topic!

I would have *NEVER* thought that LEDs can be used for something like that. The first point: Roland´s D-Beam?!? HELLO? Y?

And when you think of the possibilities (like a matrix of LED touchpad where the lighting level of let´s say every second LED depends on how near you are etc.). The only prob I can think about right now is how the heck do they bring away the background light well? Especially if it changes (during a long night when the sun gets back up).

And: Why the heck is something like that not used in MUCH more applications (you can think of so DAMN much stuff where that could be implemented).

Anyhow: Thnx for those links!

[moogah]

There must be a catch to it, but it looks like it can easily be overcome.  To cancel out the background light you'd simply need one sensor that isn't part of the array to set the ambient level, and measure relative to that.

[DrBunsen]

Wow.  I've got about 40 of those 8x8 arrays in a box somewhere.  Knew I saved them for a reason

[justDIY]

Hi gang

DrBusen dropped me a line on my blog, so I thought I'd say hi!

If anyone is interested in building an interface similar to whats documented on my blog (link in previous post), I'd be happy to share source code and/or schematics - my email is gordonthree (a) gmail.com

The data my interface outputs is basicly a number between 0 and ~35000 ... but with the practical numbers between 7000 and 25000... and you get a BUNCH of those numbers, one for every sensor in your array.  I'm not really sure how you translate that into some sort of usful analog input (like a slider).  I did manage to do some simple math on the data to make the interface work as a large group of switches,  so they can each be on or off depending on if your finger is present or not.

I've worked around ambient light by basiclly 'recalibrating' the interface every few 100 mS ... so the sensor that is 'darkest' sets the ambient light level, which is then subtracted from all the sensors to get a 'baseline', of course this method is not perfect, and in situations of strong ambient light, your finger or an object interacting with the array actually appears darker than the ambient light entering the surrounding sensors, which really messes things up.

i'm also having trouble coming up with a method to build large arrays without using a bazillion microcontrollers ... right now to do an 8x8 array would cost 7 microcontrollers (at $3 each), which is not really acceptable

ttyl

justDIY

[DrBunsen]

Hi Gordon, thanks for dropping by.

I should have included the main site's URL in my post to your blog, its http://ucapps.de/  You could possibly find a solution or at least some clues there.  Check the DIN, DOUT and AIN, AOUT scanned mulitplexing boards under MIDIbox Hardware Platform in the sidebar.   You can have up to 64 (or is it 128, I forget) analog ins per Core (PIC host) board.  There should be code for doing the scanning under MIOS.

MIOS is all PIC assembly, with a resident  bootloader so you don't have to reflash, just upload code via the MIDI/serial port.  The assembly code is modularised, all available and very well annotated.  There's also a C wrapper for higher level programming.

Some other random ideas... a single RGB LED as a 3-way detector in the centre of a triangle (or ring?) of matched, individual R, G, and B LEDs ... an X-Y touchpad using two different colours - LEDs just above and aimed horizontally across the touch area, using a linear diffuser to spread the light evenly along each axis ... same, but using bar-graph LED arrays facing each other across the touch area, one side as emitter and the other as  ... interpolating the analog values from neighbour LEDs to reduce error/increase resolution ... MIDI control surface composed entirely of bargraph LEDs, stroke the graph to drag the light bar up and down ... interpolating using components rather than code ...