Other (#5) - Custom Sensor Bars (#17) - Message List

Parts:

• Breadboard
• 10 IR LEDS (I have 2 banks of 5, Wii is 2 banks of 3)
• 10 resistors (R=V/I, see below)
• USB cable
• powered USB port

The resistors limit the current through the LEDs - for USB, V=~5V, I depends on your LEDs (ignoring the diode drop gives you a safety margin). The circuit is 10 (or 6) identical parallel paths, each consisting of a resistor and LED (LED polarities must match!). Cut open the USB cable, attach red to the anode side, black to the cathode side ( which is which?). Plug it in. Look at it through a digital camera (cell phone cameras work great) to see if it's working (CCD camera response extends to IR spectrum, strangely, though, they look blue on my phone). I'll post pictures and numbers when I have a moment. Also, see the  Wiili.org thread on this.

Warning: LEDs are cheap. The USB port on your laptop is not. If you don't properly construct the circuit and the resistance ends up being too low, and your USB port doesn't properly limit current (USB spec is 500mA, as I recall, but who knows how well that is enforced in any given implementation), you may damage the port, and possibly the rest of the machine. It would be wise to use a cheaper voltage source to test (3 AAs in series = 4.5V = close enough).

I'm using a "Two IR LEDs hooked up to a USB port" homemade bar (keep in mind though, I'm not a hardware expert. I make no guarantee to the validity of the method or reasoning behind how I determined the resistor value):

Materials: - 1 Black USB Cable 6' ( http://www.microcenter.com/single_product_results.phtml?product_id=0202327) - 1 Black 1/8" (ie headphone) Stereo (Mono would have worked too) Audio Extension Cord, really, really long (about as long as the official sensor bar's cord) - Black Electric Tape - 2 "High Intensity" IR LEDs rated at 100mA, 1.2V (from Radio Shack) - Either standard soldering equipment or 1 Pack of 22-26 guage "Butt Connectors", 8 actually used, plus a few I screwed up on ( http://www.radioshack.com/product/index.jsp?productId=2103505&cp=&sr=1&origkw=butt+connector&kw=butt+connector&parentPage=search) - 1 Resistor (forget offhand exactly what value I used, it was either 27 or 33 ohm. 33 would be safer.)

Tools: - Standard soldering equipment or Wire Crimper ( http://www.radioshack.com/product/index.jsp?productId=2062789&cp=&sr=1&origkw=crimper&kw=crimper&parentPage=search) - Automatic Wire Stripper ( http://www.twistedpairgaming.com/download/WireStripper.jpg) - Scissors

Extra Tools to help figure out resistor value: - Multimeter - Breadboard - A Whole Bunch 'o Resistors - (optional) 4 Fresh Alkaline AA's (6.0v), or 5 Charged NiMH AA's (6.0v). Or one of those big 6.0v batteries. - (optional) AA Holder - (optional) Extra IR LEDs

Construction: - (Figuring out resistor value) Use OHMs law to calculate an initial resistor value to start with, based on the LED's rated current, and assuming no resistance from the LEDs and a voltage of 5.25v (the maximum allowed for USB spec). Ie, Resistance = 5.25v / 0.1 A (100mA, the rating for my particular LEDs, but don't go above 100mA because that's the max USB allows without using the USB protocol to request more)

- Cut off the "B" plug from the USB cable. Then, strip off about an inch of the black outer plastic. Pull back and cut off the exposed metallic shielding. Strip a few millimeters off of the black (ground) and red (+5) wires, and cover the ends of the other two wires with electrical tape.

- (Figuring out resistor value) Measure the current you're getting from the initial value of resistor, and then go down to lower values until you start getting close to whichever is lower, the rating for your LEDs or 100mA (the maximum for USB without using the actual USB protocol to request more). It can be helpful to know you can cut the value of a resistor in half by putting it in parallel with another resistor of the same value. When doing all of this, start with the AA's (or skip them if you're brave) and then move onto the hacked USB cable plugged into a USB port (but, like ghostbusters' streams, MAKE SURE the red and black don't touch together or otherwise get connected without proper resistance. And, to be safe, only plug it in when you're actually testing, then unplug it).

- Cut off the plugs at both ends of the audio cable. Strip about an inch of the outer plastic off each end. Strip a few millimeters off both ends of the black and red wires (you could really just use any two wires in the audio cable. Also, sometimes there's an uncovered wire instead of a black one, doesn't matter, if you use it just make sure it doesn't touch anything else.)

- Connect the hacked end of the USB cable to one end of the audio cable: Splice the black USB wire to the black (or whatever) audio wire, and the red USB to the red (or whatever) audio. Wrap the whole connection area in electrical tape.

- Cut off the last foot (or whatever distance you want between the LEDs) of the audio cable. Strip both ends just as before.

- Do the same "splice wires and cover in electrical tape" thing for the rest of the connections:

• Black wire on long USB cord -> negative end of one LED (marked by either a flat section on the rim of the LED, or the shorter wire)
• Positive end of same LED -> black wire on the short section of audio cord
• black wire on the short section of audio cord -> negative end of other LED
• positive end of same LED -> red wire on the short section of audio cord (use electrical tape to make sure the two wires on this LED won't ever touch)
• red wire on the short section of audio cord -> either end of resistor
• other end of resistor -> red end of long USB cord (use electrical tape to make sure two wires on this resistor won't ever touch the wires on the first LED)

- Plug in, use digital camera (if available) to make sure the LEDs are lit, and enjoy.

Results: Official Bar on Wii: Works fine, obviously. Homemade Bar on Wii: No noticable difference from official bar Official Bar on PC: Haven't tried. Homemade Bar on PC: Works ok, but kinda iffy.

I'm fairly certain the iffyness of the homemade bar on the PC is just because of CWiid's "work-in-progress" IR ptr capabilities, due to it working fine on the Wii and due to other reports on these forums of CWiid's IR handling being a imperfect. I'll have to try the homemade bar on my Windows machine using GlovePIE when I get a chance.

What I'd like to know: What would happen if one of the LEDs burs out? I assume (and hope) it creates an open circuit. Because otherwise, I'd end up drawing too much current and blow out the other LED. Not sure about the USB port. The USB spec allows a draw of up to 500mA (or more?) but doesn't allow any more than 100mA without using the actual USB protocol to request more power (source: Wikipedia). Of course, using an unpowered USB hub could through another wrench into the works.

I hope this post wasn't complete gibberish :/