Phototransistor Multitouch With A Twist


[Alex] sent us this project he’s working on where he’s building a phototransistor based multitouch input system. Though many people have built systems with phototransistors, most of them are quite large and very sensitive light and dark variances. [Alex] has done some fancy background subtraction through software. He believes his is the first to do this. As you can see in the video after the break, it seems impervious to the lamp he is moving around, and still fairly sensitive to his hand. We’re curious to see where he takes this one.


9 thoughts on “Phototransistor Multitouch With A Twist

  1. Very good.

    My 1st thought for application would be some type of air piano/synthesizer (musical interface). You could also use it to control the tilting of a plane, ie: Mercury Meltdown for wii

    I may be wrong, but couldn’t this also be used as a sort of 3d imaging? Albeit the resolution is dependent of the amount and the size of the ptrans.

  2. Not quite sure if that’s really “multi-touch,” as I’m not seeing much variation of places he’s touching and places his hand is just over. That has got its uses, but probably not for multi-touch interfaces as we know it right now. Maybe putting a diffusing plastic above the sensors would make it more to what I’m thinking of, only detecting the actual points you literally touch.

  3. Hi(I’m the one that built this)

    36chambers: Yes, it could be used for both of those things. Its probably not fast enough at the moment to be used for musical composition, but it could certainly work for 3d imaging. Albeit this one wouldn’t work very well, it doesn’t have a high enough resolution, like you said.

    Darkfader, Ciberwizz: No, this one is not really multi-touch. The purpose of this was to test a bunch of different phototransistors to see which one worked best for my purposes. I am currently waiting on BatchPCB to send me my circuit board so I can begin work on a larger one. I have also tried using lasers instead of LEDs(so its an LLP effect instead of a DI effect). That works really well, but not so much for this specific example because the rows are spaced so far apart.

    Thanks everyone!

  4. hmm.. maybe use the SMD phototransistors from smashed road light PCBs (the little squre transistor based PCB) … i have a load someplace, can i find them maybe and try it?

    these can be purchased from various suppliers, and are often used on laser printers etc as rotary sensors.

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