Plans for the Desk

EDIT AGAIN: Scratch the whole array idea entirely. I just found a method at NUI group that uses photoresistors (i.e. fast scanning), but only requires them along the edge. Even though they are on the edge there are no occlusion problems as one might expect because of some magic with polarizing film. Will post updates soon.

EDIT: Well it seems that the rise time on photoresistors is generally about 60 ms. This is a hit on the response time of the screen. Basically what that means is no matter how fast we sample the matrix, true response is limited to about 16 fps. So the goal is to either find a photoresistor which is cheap and has a rise time of ~10ms -> 100fps, or else think of a new sensing system.

First of all, we (or maybe just I) plan on finishing the first desk by the end of Christmas break, but I have some ideas for the next version of the desk that I'll talk about now. The major improvement I want to make is to the size. The first version of the desk is about a foot and a half deep because of the distance requirement of the camera from the screen. So the first step in making a thin desk is eliminating the camera from the design.

Obviously, we need some sort of visual sensor to replace the camera, so the option we will try is to make a large array of analog light sensors (photocell network) underneath the screen. A micro-controller will then read the value of each sensor sequentially and use an algorithm to deduce the location of blobs. The circuit underneath the screen will look something like this. To select a column, the MCU puts a voltage on one of the top pins, and a high impedance on the others. Then, to read a specific sensor, the MCU puts one of the row outputs through an analog-to-digital converter (using a multiplexer in between).

So far it seems that diodes are required on every photocell in order to prevent current from flowing through the other resistors. I simulated the circuit and it seems that the back-flow was somewhat negligible, especially in larger matrixes, but diodes are cheap, and precision is good, so I will keep them.

The other concern is the cost and difficulty of construction. For the first version of the desk I want to use a 32x24 matrix of photocells, so there are 768 cells that need to be purchased and soldered. So far the cheapest I have been able to find are $0.32 for large volume orders. I would be very glad to find one closer to $0.20, bringing the cost for all resistors down to $150. The diodes and resistors needed don't total to be more than $10-$15, so they aren't a problem. I was thinking I might be able to use my lab's rapid prototyping machine to fabricate the PCB and solder all of the components onto it.

Berlin Delays

Unfortunately summer vacation was not long enough. We were just about finished with the desk prototype when we ran into some last-minute problems. The last minor electronics job involved separating two of the monitors circuit boards and connecting them with an independently assembled ribbon cable. We doubled up on ribbon cable headers just in case but we broke both of them anyways. Also the monitor lost about 1/10 of its pixels but that's actually not the biggest problem.

It doesn't look like there's any way we can finish this before the first break this Fall. So fall break is our currently planned finish date for the project. Good news is that we're planning on starting some Android development while at Purdue! Wish us Purdue Freshman Godspeed and keep checking the blog for upcoming project updates.

The Behemoth

So we made a quite of a bit of progress this morning. We remade the base of the screen out of one big piece of wood and then attached all of the LED's to it.

Project Berlin

The project we're working on now is a prototype high-tech school desk. The idea was proposed by Kendal Smith, a Chemistry teacher at our high school. The general concept is this: a desk in which the surface is a touch screen computer (à la Microsoft Surface) and the computer runs education-oriented software (distribution of learning materials, test taking, digital homework, etc.)

To accomplish the multitouch aspect we're using a method called FTIR Touch Sensing developed at NYU. In this method, a sheet of plexiglass is flooded with IR light. When your fingers make contact with the sheet the IR light is scattered and shined into an IR-sensing camera below. The image is used by the computer to determine the location of the touches.

Most DIY systems use a rear projector and a layer of silicone-coated drafting vellum above the plexiglass to project the image onto. The silicone also creates good contact between your finger and the surface. We are instead using a simple LCD to cut costs. This presents a few problems which we haven't yet solved, most notably a method for backlighting the display, and a material besides vellum to help with finger contact.

To accomplish the software aspect we will first be using Touchlib and Windows 7. The long-term goal is to use our own operating system known as Oceania which is a glorified Newspeak Programming Language virtual machine that will run education software and have built in support for multitouch. I'll let Ryan write the first post on the Oceania project.

You can see the progress we've made so far in the previous post on blobs. As we make more progress we'll keep you posted. Jason, Ryan, and I are working on this project.

First Blobs

Here are the first couple screenshots from the PS3 Eye camera. These are images related to project "Berlin" which consists of the creation of a desk who's surface is a multitouch display. The end result is hopefully something education-related as the idea was conceived by my high school Chemistry teacher Kendal Smith. More on the project in later posts.

The following first images are blurry because they were taken by our first camera. It was damaged because I tried to dig out what I thought was an IR filter but which was actually part of the lens.

This last image is from the newer camera that is still in tact. You can clearly see led strips surrounding the display and the blobs of infrared light where Keegan's fingers touch the screen.