Monday, June 22, 2009

DnD: Digital Game Table - Update

This weekend I tried connecting the Wii-mote to the computer using Smoothboard. No problems there (the pop-up for the unregistered version is annoying, though) and the pen worked when using it on the monitor with the Wii-mote about 1.5' to 2' away.

I did notice, however, that before long, the N-cell alkaline battery on the pen started getting really hot, really quick. Not being an experienced electrician, I had combined a 1.2v LED with a 1.5v battery - too much voltage for the LED. So I went to Radio Shack to find a resistor. Sadly, the guy working there was no help ("I'm not an electrician, just a dude with a drawer full of resistors." - seriously, he said that).

In doing some reading on the 'net before hand, I saw a post somewhere saying that 75 ohms should be fine. They didn't have a 75 ohm resistor, so I purchased some 100 ohm (1/2 watt 5% tolerance) resistors instead - better safe than sorry, right? It eliminated the heat issue with the battery and I could still see the light on my cell-phone cam (remember, IR light can't be seen by humans). The question is: what if it's too much resistance? Will it reduce the intensity of the IR-LED? EDIT: I double-checked, the resistors are 100 ohm, NOT 100K ohm.

Anyway, I taped the Wii-mote to the projector, right above the lens and aimed at the mirror. Unfortunately, I could not pick up the light from the surface of the table. I think the white protective film I left on one side of the 1/4" plexiglass may be too thick for the light to shine through, but I'm not sure. My cell phone camera can pick up a faint spot of light, but I have no way of knowing intense it needs to be for the Wii-mote - obviously more than it is currently. I need to test it on the clear plexiglass and with other translucent substances - such as tracing paper - to verify. I may also want to get a smaller resistor for the pen.

Trying to figure out where I screwed up . . . *sigh* I always hate this part.

Here are two links I've found that have made me a bit more resistor-savvy:
- Electronics 101 - Basics for those who want to make their own IR-Pen
- LED calculator: current limiting resistor value

* Sorry for the lack of pics lately, my digital camera is on the fritz again - something else I have to take apart and fix . . . again. >_<

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