Open Source Interface

A different multitouch proposal

2008-08-25T16:55:40-05:00

I was wondering if anyone else had come up with this idea yet. Or if anyone had already tried this and found it didn’t work. This is not a Cam and IR setup. In addition, it would lend itself well to either hardware or software blob detection. At least better than cam and IR does. See attachment for a picture as to the setup.

A plane of light would still be produced just like in LLP or a typical FTIR setup could potentially work. If fact, depending on your FTIR setup it may only be slightly difficult to perform this upgrade, once the extra materials to do this are available. Then along the edges either LEDs with a negative voltage and current, or photodiodes could be placed to receive the IR light. Whenever a finger is placed in the path of the light the voltage/current produced by the photoreceiver would be diminished. These photoreceivers could then be fed to an ADC and then processed. As an output the point locations could be transmitted.

The below sketchup assumes a 5mm led is used with a 2mm spacing between each LED. The 2mm spacing is probable a little optimistic.
The circles placed along the edges are the LEDs.
The boxes at the corner are the lasers(these are not to scale!)
The inner most box represents the touch surface.
The larger outer box is the path the lights from the ideal lasers.

everything other than the fingers and lasers are to scale.

If more info is needed ask.
Also see here for an example.
http://www.cs.nyu.edu/~jhan/ledtouch/index.html

Could someone please verify my LED Ordering

2008-10-14T12:47:10-05:00

I just read some posts about how to calculate the resistor strength. It’s been some time since I visited an electronics class. Most of what I have learned there has been overwritten by
object oriented programming and uh I am sorry to say… accounting skills. At least I will be able to correctly depreciate the table if I fry my LED arrangement!

We are planing on using these LEDs (I read there quite good for a FTIR Table)
Osram 485p (40 degrees)
http://www2.produktinfo.conrad.com/datenblaetter/150000-174999/153831-da-01-ml-IR-Emitter_SFH485P_de-en.pdf

It says the leds have a forward voltage of 1.5 V and a forward current of 100 mA.

Using a 12 V input the calculator tells me I need a 1 ohm resistor:

http://ledcalculator.net/default.aspx?values=12,1.5,100,120,0

It also says:
You will need 15 x 1 ohm 1/8 watt resistors.

I read somewhere that I can use 1/4 watt resistors as this number merly indicates the maximum watt strength it can handle. So a 1/4 watt resistor can handle the 1/8 watts needed.

Is this calculation correct or do I have a fundamental error in it?

Thanks in advance for any help!

tikitag: Cheap RFID Reader

2008-10-05T22:58:56-05:00

Just found this on MAKE Blog:

http://www.tikitag.com/

I don’t know if they have an API, or what systems it will run on, but its cheap, USB, and standalone.

Voltage or current source?

2008-10-07T15:53:28-05:00

Does anybody know if a LED will work better with a current controlled source (as opposed to just connect with a voltage source). The advantage of a currant source that I can think of is that it’s a good way of keeping a constant currant for the LEDs (constant lighting as well as protection from to much current). A voltage source could have small voltage changes, however current could change alot because of the non-linear properties of LEDs.

What do you think?

More or less resistance?

2008-09-19T17:06:21-05:00

I have a dilemma. My local RadioShack has resistors near what I need, but not exactly what I need for wiring my LEDs.

I plan on wiring my LEDs to a 12 VDC power supply. My LEDs are 1.4 V 100 mW. I used the LED calculator to determine the ohms and watts of resistors that I would need if I ran different numbers of LEDs in series off of the 12 V power.

If I run 8 LEDs in series (ideal) I would need an 8.2 Ohm 1/8 W resistor.
They have 10 Ohm 1/8 W. (25% more resistance)

If I run 7 LEDs in series (OK) I would need a 22 Ohm 1/4 W resistor.
They have 10 Ohm 1/4 W. (9% less resistance with two)

If I run 6 LEDs in series (lots of soldering) I would need a 36 Ohm 1/2 W resistor.
They have 15 Ohm, 33 Ohm, and 10 Ohm in 1/2 W resistors. (8.3% less resistance with a single 33, 2.8% less resistance with two 10 Ohm and one 15 Ohm resistor)

My question is can I put two resistors inline and create more resistance. And if so what would be the best for me to use from what RadioShack has? I can get slightly more or slightly less resistance, but not exact.

* All resistors are +/- 5%

Thanks,
Mike

Local place to buy resistors?

2008-09-18T19:42:33-05:00

What kind of shop sells resistors locally? Would it be an electrical supply store? I don’t think that they would carry resistors for small electronics. I am looking for a place locally to buy 8.2 ohm 1/8 watt resistors. The closest thing I have to me that I know of that is remotely electronics oriented is Radio Shack and I am sure they don’t have these. I could order them off the Internet, pay 35 - 50 dollars for next day shipping and have them by Monday, but I would much rather pay 3 - 5 dollars plus tax and have them tomorrow. Any ideas.

I live in Mocksville, North Carolina by the way. The zip code is 27028. Just in case someone lives in North Carolina and knows a place near by.

Thanks.

Want to get your hands on some e-Paper on October? Esquire Magazine are publishing their 75th edition with an epaper front cover!

2008-09-06T14:35:16-05:00

http://gadgets.boingboing.net/2008/07/30/esquire-to-geeks-hac.html
I really hope this is hackable. I think i’ll buy a couple of copies just incase!

Brain Interfaces!

2008-08-26T12:00:23-05:00

I thought some of you might find this paper interesting, it’s a summary of current computer brain interfaces. I’m quite interested in the potential of cheap non-invasive diy applications. It can’t be too long before we find a reliable, cheap and non-invasive method of interfacing with our brains without having to wear one of those silly looking hats!

http://www.wtec.org/bci/BCI-finalreport-10Oct2007-lowres.pdf

I look forward to the day when there’s a nuigroup like community for experimenting with this stuff

There’s also an open-source software kit for doing this kind of research:

http://www.bci2000.org/BCI2000/Features.html

LED calculator

2008-05-18T12:38:55-05:00

I’m considering using a 9V battery for my design. I would use solderless LED holders for my 18 SFP485P IR lights. I’ve been to the calculator and I’m not sure I exactly trust it. Could it be that this picture is right? Only 1 ohm resistors?

Quick question about how infared LED Lights work

2008-09-01T19:21:10-05:00

I just wanted to make sure I have this understood rite so Im not going down the wrong path.

the infered light is invisible to us but webcams can pick it up by setting camera settings to dark contrast to the images its reciveing..

is this rite ??? :/